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Updates in flutter/shell for the shell refactor (Patch 9) #4837
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This changes is part of a large patch for easier review. Try the whole patch in one go by checking out https://github.com/chinmaygarde/flutter_engine/tree/shell directly. This patch contains the following changes: * Fairly mechanical removal of singletons used to access the task runners referneces for various thread specific tasks. These task runners can be queried on the shell. * Engine, Animator, PlatformView and Rasterizer use a delegation mechanism which the shell implmenets to access various resources that used to be singletons. There are significant opportunities to cleanup this code in the future. * Engines can be launched with a separate RunConfiguration instead of having various overrides for each variant. * Added documentation to some switches that were missing the same. * Remove platform specific impelemtations of flutter_tester in favor of one executable target for all platforms. * Update various platform specific backend to account for the new Shell and PlatformView API.
This patch contains a mostly mechanical move of the code in various platforms to account for the updated API. This still turned out to be a larger patch than I anticipated. Happy to chop it up further for easier review. |
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Overall design LGTM
Noticed some regressions while experimenting with the patch:
- Video isn't playing in Gallery
- flutter_tester is exiting with an assert when running a script:
Check failed: vm_snapshot_ && vm_snapshot_->IsValid(). VM snapshot must be valid.
shell/common/rasterizer.cc
Outdated
} | ||
|
||
if (data == nullptr) { | ||
FXL_DLOG(INFO) << "Sceenshot data will null."; |
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should be "was null"
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Done.
shell/common/engine.cc
Outdated
if (legacy_sky_platform_) { | ||
// TODO: Remove this legacy call along with the platform. This is what makes | ||
// the engine unable to run from multiple threads in the legacy | ||
// configuration. The microtask handler are still in this initializer still. |
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remove the second "still"
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Done. The entire comment is incorrect because the microtask handlers have been moved to the settings anyway.
I can get flutter_tester to load scripts on Linux by modifying NativeLibrary::ResolveSymbol to special case the Dart snapshot symbols (kDartVmSnapshot{Data,Instructions} and kDartIsolateSnapshot{Data,Instructions}) and resolve them using the global declarations from flutter/lib/snapshot/snapshot.h Loading kernels isn't working yet - will need to debug further |
Hmm, I thought I got flutter_tester with --preview-dart-2 working already. Will investigate and fix. Thanks for the heads up on video. I think I only checked on iOS. Patching both. |
To get video playing on Android, call |
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I tried patching the embedder API to load kernels and had a few more comments
shell/platform/embedder/embedder.cc
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// Step 3: Run the engine. | ||
shell::RunConfiguration run_configuration( | ||
shell::IsolateConfiguration::CreateForSource( |
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Change this to call RunConfiguration::InferFromSettings
. settings
will also need to configure kernel_snapshot_path
and application_kernel_path
if a kernel is present in the assets directory.
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Done.
shell/common/run_configuration.h
Outdated
std::unique_ptr<IsolateConfiguration> TakeIsolateConfiguration(); | ||
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private: | ||
std::unique_ptr<IsolateConfiguration> run_configuration_; |
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Rename this to isolate_configuration_
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Done.
{ | ||
std::vector<uint8_t> kernel; | ||
if (asset_manager && | ||
asset_manager->GetAsBuffer(settings.application_kernel_path, &kernel)) { |
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Is application_kernel_path intended to be a filesystem path or an asset name?
In embedders like Android's FlutterMain::Init
it's set as a filesystem path, but here it's consumed as an asset name
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Note to self: Make this application kernel asset.
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Renamed to application_kernel_asset.
Fixed video on all platforms by making MarkNewFrameAvailable be called by the base platform view implementation on the flow::Texture. |
I've patched in these changes, and while video is now working I can also more easily repro the crash whenever the app restarts while video is running.
|
settings.task_observer_remove = [](intptr_t key) { | ||
fml::MessageLoop::GetCurrent().RemoveTaskObserver(key); | ||
}; | ||
|
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The embedder needs to check for the presence of a kernel and configure settings
with the kernel asset paths:
Example:
const char kVMKernelSnapshotFileName[] = "platform.dill";
const char kApplicationKernelSnapshotFileName[] = "kernel_blob.bin";
std::string platform_kernel_path =
fml::paths::JoinPaths({settings.assets_path, kVMKernelSnapshotFileName});
std::string application_kernel_path = fml::paths::JoinPaths(
{settings.assets_path, kApplicationKernelSnapshotFileName});
if (files::IsFile(platform_kernel_path) &&
files::IsFile(application_kernel_path)) {
settings.kernel_snapshot_path = platform_kernel_path;
settings.application_kernel_asset = kApplicationKernelSnapshotFileName;
}
@jonahwilliams the video JNI exception is happening because In this patch @chinmaygarde the texture registry |
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static std::string CreateAndroidShellLabel(intptr_t handle) { | ||
std::stringstream stream; | ||
stream << "io.flutter.0x" << std::hex << handle; |
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Remove the "io.flutter.0x" prefix - Linux thread names are limited to 16 characters
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Done. Still kept a count so that the number of the engine shows up in the native thread traces.
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Also updated the behavior for iOS.
Addressed the crashes while collecting external textures using @jason-simmons ' recommendation. |
All comments addressed. PTAL. |
This may be a problem with the video plugin - but video does not restart when hiding the activity and then reopening it. I can fix the problem by navigating away and back, so it isn't fatal |
The Flutter Engine currently works by initializing a singleton shell instance. This shell has to be created on the platform thread. The shell is responsible for creating the 3 main threads used by Flutter (UI, IO, GPU) as well as initializing the Dart VM. The shell, references to task runners of the main threads as well as all snapshots used for VM initialization are stored in singleton objects. The Flutter shell only creates the threads, rasterizers, contexts, etc. to fully support a single Flutter application. Current support for multiple Flutter applications is achieved by making multiple applications share the same resources (via the platform views mechanism). This scheme has the following limitations: * The shell is a singleton and there is no way to tear it down. Once you run a Flutter application in a process, all resources managed by it will remain referenced till process termination. * The threads on which the shell performs its operations are all singletons. These threads are never torn down and multiple Flutter applications (if present) have to compete with one another on these threads. * Resources referenced by the Dart VM are leaked because the VM isn't shutdown even when there are no more Flutter views. * The shell as a target does not compile on Fuchsia. The Fuchsia content handler uses specific dependencies of the shell to rebuild all the shell dependencies on its own. This leads to differences in frame scheduling, VM setup, service protocol endpoint setup, tracing, etc.. Fuchsia is very much a second class citizen in this world. * Since threads and message loops are managed by the engine, the engine has to know about threading and platform message loop interop on each supported platform. Specific updates in this patch: * The shell is no longer a singleton and the embedder holds the unique reference to the shell. * Shell setup and teardown is deterministic. * Threads are no longer managed by the shell. Instead, the shell is given a task runner configuration by the embedder. * Since the shell does not own its threads, the embedder can control threads and the message loops operating on these threads. The shell is only given references to the task runners that execute tasks on these threads. * The shell only needs task runner references. These references can be to the same task runner. So, if the embedder thinks that a particular Flutter application would not need all the threads, it can pass references to the same task runner. This effectively makes Flutter application run in single threaded mode. There are some places in the shell that make synchronous calls, these sites have been updated to ensure that they don’t deadlock. * The test runner and the headless Dart code runner are now Flutter applications that are effectively single threaded (since they don’t have rendering concerns of big-boy Flutter application). * The embedder has to guarantee that the threads and outlive the shell. It is easy for the embedder to make that guarantee because shell termination is deterministic. * The embedder can create as many shell as it wants. Typically it creates a shell per Flutter application with its own task runner configuration. Most embedders obtain these task runners from threads dedicated to the shell. But, it is entirely possible that the embedder can obtain these task runners from a thread pool. * There can only be one Dart VM in the process. The numerous shell interact with one another to manage the VM lifecycle. Once the last shell goes away, the VM does as well and hence all resources associated with the VM are collected. * The shell as a target can now compile and run on Fuchsia. The current content handler has been removed from the Flutter engine source tree and a new implementation has been written that uses the new shell target. * Isolate management has been significantly overhauled. There are no owning references to Dart isolates within the shell. The VM owns the only strong reference to the Dart isolate. The isolate that has window bindings is now called the root isolate. Child isolates can now be created from the root isolate and their bindings and thread configurations are now inherited from the root isolate. * Terminating the shell terminates its root isolates as well as all the isolates spawned by this isolate. This is necessary be shell shutdown is deterministic and the embedder is free to collect the threads on which the isolates execute their tasks (and listen for mircrotasks flushes on). * Launching the root isolate is now significantly overhauled. The shell side (non-owning) reference to an isolate is now a little state machine and illegal state transitions should be impossible (barring construction issues). This is the only way to manage Dart isolates in the shell (the shell does not use the C API is dart_api.h anymore). * Once an isolate is launched, it must be prepared (and hence move to the ready phase) by associating a snapshot with the same. This snapshot can either be a precompiled snapshot, kernel snapshot, script snapshot or source file. Depending on the kind of data specified as a snapshot as well as the capabilities of the VM running in the process, isolate preparation can fail preparation with the right message. * Asset management has been significantly overhauled. All asset resolution goes through an abstract asset resolver interface. An asset manager implements this interface and manages one or more child asset resolvers. These asset resolvers typically resolve assets from directories, ZIP files (legacy FLX assets if provided), APK bundles, FDIO namespaces, etc… * Each launch of the shell requires a separate and fully configured asset resolver. This is necessary because launching isolates for the engine may require resolving snapshots as assets from the asset resolver. Asset resolvers can be shared by multiple launch instances in multiple shells and need to be thread safe. * References to the command line object have been removed from the shell. Instead, the shell only takes a settings object that may be configured from the command line. This makes it easy for embedders and platforms that don’t have a command line (Fuchsia) to configure the shell. Consequently, there is only one spot where the various switches are read from the command line (by the embedder and not the shell) to form the settings object. * All platform now respect the log tag (this was done only by Android till now) and each shell instance have its own log tag. This makes logs from multiple Flutter application in the same process (mainly Fuchsia) more easily decipherable. * The per shell IO task runner now has a new component that is unfortunately named the IOManager. This component manages the IO GrContext (used for asynchronous texture uploads) that cooperates with the GrContext on the GPU task runner associated with the shell. The IOManager is also responsible for flushing tasks that collect Skia objects that reference GPU resources during deterministic shell shutdown. * The embedder now has to be careful to only enable Blink on a single instance of the shell. Launching the legacy text layout and rendering engine multiple times is will trip assertions. The entirety of this runtime has been separated out into a separate object and can be removed in one go when the migration to libtxt is complete. * There is a new test target for the various C++ objects that the shell uses to interact with the Dart VM (the shell no longer use the C API in dart_api.h). This allows engine developers to test VM/Isolate initialization and teardown without having the setup a full shell instance. * There is a new test target for the testing a single shell instances without having to configure and launch an entire VM and associated root isolate. * Mac, Linux & Windows used to have different target that created the flutter_tester referenced by the tool. This has now been converted into a single target that compiles on all platforms. * WeakPointers vended by the fml::WeakPtrFactory(notice the difference between the same class in the fxl namespace) add threading checks on each use. This is enabled by getting rid of the “re-origination” feature of the WeakPtrFactory in the fxl namespace. The side effect of this is that all non-thread safe components have to be created, used and destroyed on the same thread. Numerous thread safety issues were caught by this extra assertion and have now been fixed. * Glossary of components that are only safe on a specific thread (and have the fml variants of the WeakPtrFactory): * Platform Thread: Shell * UI Thread: Engine, RuntimeDelegate, DartIsolate, Animator * GPU Thread: Rasterizer, Surface * IO Thread: IOManager This patch was reviewed in smaller chunks in the following pull requests. All comments from the pulls requests has been incorporated into this patch: * flutter/assets: flutter#4829 * flutter/common: flutter#4830 * flutter/content_handler: flutter#4831 * flutter/flow: flutter#4832 * flutter/fml: flutter#4833 * flutter/lib/snapshot: flutter#4834 * flutter/lib/ui: flutter#4835 * flutter/runtime: flutter#4836 * flutter/shell: flutter#4837 * flutter/synchronization: flutter#4838 * flutter/testing: flutter#4839
The Flutter Engine currently works by initializing a singleton shell instance. This shell has to be created on the platform thread. The shell is responsible for creating the 3 main threads used by Flutter (UI, IO, GPU) as well as initializing the Dart VM. The shell, references to task runners of the main threads as well as all snapshots used for VM initialization are stored in singleton objects. The Flutter shell only creates the threads, rasterizers, contexts, etc. to fully support a single Flutter application. Current support for multiple Flutter applications is achieved by making multiple applications share the same resources (via the platform views mechanism). This scheme has the following limitations: * The shell is a singleton and there is no way to tear it down. Once you run a Flutter application in a process, all resources managed by it will remain referenced till process termination. * The threads on which the shell performs its operations are all singletons. These threads are never torn down and multiple Flutter applications (if present) have to compete with one another on these threads. * Resources referenced by the Dart VM are leaked because the VM isn't shutdown even when there are no more Flutter views. * The shell as a target does not compile on Fuchsia. The Fuchsia content handler uses specific dependencies of the shell to rebuild all the shell dependencies on its own. This leads to differences in frame scheduling, VM setup, service protocol endpoint setup, tracing, etc.. Fuchsia is very much a second class citizen in this world. * Since threads and message loops are managed by the engine, the engine has to know about threading and platform message loop interop on each supported platform. Specific updates in this patch: * The shell is no longer a singleton and the embedder holds the unique reference to the shell. * Shell setup and teardown is deterministic. * Threads are no longer managed by the shell. Instead, the shell is given a task runner configuration by the embedder. * Since the shell does not own its threads, the embedder can control threads and the message loops operating on these threads. The shell is only given references to the task runners that execute tasks on these threads. * The shell only needs task runner references. These references can be to the same task runner. So, if the embedder thinks that a particular Flutter application would not need all the threads, it can pass references to the same task runner. This effectively makes Flutter application run in single threaded mode. There are some places in the shell that make synchronous calls, these sites have been updated to ensure that they don’t deadlock. * The test runner and the headless Dart code runner are now Flutter applications that are effectively single threaded (since they don’t have rendering concerns of big-boy Flutter application). * The embedder has to guarantee that the threads and outlive the shell. It is easy for the embedder to make that guarantee because shell termination is deterministic. * The embedder can create as many shell as it wants. Typically it creates a shell per Flutter application with its own task runner configuration. Most embedders obtain these task runners from threads dedicated to the shell. But, it is entirely possible that the embedder can obtain these task runners from a thread pool. * There can only be one Dart VM in the process. The numerous shell interact with one another to manage the VM lifecycle. Once the last shell goes away, the VM does as well and hence all resources associated with the VM are collected. * The shell as a target can now compile and run on Fuchsia. The current content handler has been removed from the Flutter engine source tree and a new implementation has been written that uses the new shell target. * Isolate management has been significantly overhauled. There are no owning references to Dart isolates within the shell. The VM owns the only strong reference to the Dart isolate. The isolate that has window bindings is now called the root isolate. Child isolates can now be created from the root isolate and their bindings and thread configurations are now inherited from the root isolate. * Terminating the shell terminates its root isolates as well as all the isolates spawned by this isolate. This is necessary be shell shutdown is deterministic and the embedder is free to collect the threads on which the isolates execute their tasks (and listen for mircrotasks flushes on). * Launching the root isolate is now significantly overhauled. The shell side (non-owning) reference to an isolate is now a little state machine and illegal state transitions should be impossible (barring construction issues). This is the only way to manage Dart isolates in the shell (the shell does not use the C API is dart_api.h anymore). * Once an isolate is launched, it must be prepared (and hence move to the ready phase) by associating a snapshot with the same. This snapshot can either be a precompiled snapshot, kernel snapshot, script snapshot or source file. Depending on the kind of data specified as a snapshot as well as the capabilities of the VM running in the process, isolate preparation can fail preparation with the right message. * Asset management has been significantly overhauled. All asset resolution goes through an abstract asset resolver interface. An asset manager implements this interface and manages one or more child asset resolvers. These asset resolvers typically resolve assets from directories, ZIP files (legacy FLX assets if provided), APK bundles, FDIO namespaces, etc… * Each launch of the shell requires a separate and fully configured asset resolver. This is necessary because launching isolates for the engine may require resolving snapshots as assets from the asset resolver. Asset resolvers can be shared by multiple launch instances in multiple shells and need to be thread safe. * References to the command line object have been removed from the shell. Instead, the shell only takes a settings object that may be configured from the command line. This makes it easy for embedders and platforms that don’t have a command line (Fuchsia) to configure the shell. Consequently, there is only one spot where the various switches are read from the command line (by the embedder and not the shell) to form the settings object. * All platform now respect the log tag (this was done only by Android till now) and each shell instance have its own log tag. This makes logs from multiple Flutter application in the same process (mainly Fuchsia) more easily decipherable. * The per shell IO task runner now has a new component that is unfortunately named the IOManager. This component manages the IO GrContext (used for asynchronous texture uploads) that cooperates with the GrContext on the GPU task runner associated with the shell. The IOManager is also responsible for flushing tasks that collect Skia objects that reference GPU resources during deterministic shell shutdown. * The embedder now has to be careful to only enable Blink on a single instance of the shell. Launching the legacy text layout and rendering engine multiple times is will trip assertions. The entirety of this runtime has been separated out into a separate object and can be removed in one go when the migration to libtxt is complete. * There is a new test target for the various C++ objects that the shell uses to interact with the Dart VM (the shell no longer use the C API in dart_api.h). This allows engine developers to test VM/Isolate initialization and teardown without having the setup a full shell instance. * There is a new test target for the testing a single shell instances without having to configure and launch an entire VM and associated root isolate. * Mac, Linux & Windows used to have different target that created the flutter_tester referenced by the tool. This has now been converted into a single target that compiles on all platforms. * WeakPointers vended by the fml::WeakPtrFactory(notice the difference between the same class in the fxl namespace) add threading checks on each use. This is enabled by getting rid of the “re-origination” feature of the WeakPtrFactory in the fxl namespace. The side effect of this is that all non-thread safe components have to be created, used and destroyed on the same thread. Numerous thread safety issues were caught by this extra assertion and have now been fixed. * Glossary of components that are only safe on a specific thread (and have the fml variants of the WeakPtrFactory): * Platform Thread: Shell * UI Thread: Engine, RuntimeDelegate, DartIsolate, Animator * GPU Thread: Rasterizer, Surface * IO Thread: IOManager This patch was reviewed in smaller chunks in the following pull requests. All comments from the pulls requests has been incorporated into this patch: * flutter/assets: flutter#4829 * flutter/common: flutter#4830 * flutter/content_handler: flutter#4831 * flutter/flow: flutter#4832 * flutter/fml: flutter#4833 * flutter/lib/snapshot: flutter#4834 * flutter/lib/ui: flutter#4835 * flutter/runtime: flutter#4836 * flutter/shell: flutter#4837 * flutter/synchronization: flutter#4838 * flutter/testing: flutter#4839
The Flutter Engine currently works by initializing a singleton shell instance. This shell has to be created on the platform thread. The shell is responsible for creating the 3 main threads used by Flutter (UI, IO, GPU) as well as initializing the Dart VM. The shell, references to task runners of the main threads as well as all snapshots used for VM initialization are stored in singleton objects. The Flutter shell only creates the threads, rasterizers, contexts, etc. to fully support a single Flutter application. Current support for multiple Flutter applications is achieved by making multiple applications share the same resources (via the platform views mechanism). This scheme has the following limitations: * The shell is a singleton and there is no way to tear it down. Once you run a Flutter application in a process, all resources managed by it will remain referenced till process termination. * The threads on which the shell performs its operations are all singletons. These threads are never torn down and multiple Flutter applications (if present) have to compete with one another on these threads. * Resources referenced by the Dart VM are leaked because the VM isn't shutdown even when there are no more Flutter views. * The shell as a target does not compile on Fuchsia. The Fuchsia content handler uses specific dependencies of the shell to rebuild all the shell dependencies on its own. This leads to differences in frame scheduling, VM setup, service protocol endpoint setup, tracing, etc.. Fuchsia is very much a second class citizen in this world. * Since threads and message loops are managed by the engine, the engine has to know about threading and platform message loop interop on each supported platform. Specific updates in this patch: * The shell is no longer a singleton and the embedder holds the unique reference to the shell. * Shell setup and teardown is deterministic. * Threads are no longer managed by the shell. Instead, the shell is given a task runner configuration by the embedder. * Since the shell does not own its threads, the embedder can control threads and the message loops operating on these threads. The shell is only given references to the task runners that execute tasks on these threads. * The shell only needs task runner references. These references can be to the same task runner. So, if the embedder thinks that a particular Flutter application would not need all the threads, it can pass references to the same task runner. This effectively makes Flutter application run in single threaded mode. There are some places in the shell that make synchronous calls, these sites have been updated to ensure that they don’t deadlock. * The test runner and the headless Dart code runner are now Flutter applications that are effectively single threaded (since they don’t have rendering concerns of big-boy Flutter application). * The embedder has to guarantee that the threads and outlive the shell. It is easy for the embedder to make that guarantee because shell termination is deterministic. * The embedder can create as many shell as it wants. Typically it creates a shell per Flutter application with its own task runner configuration. Most embedders obtain these task runners from threads dedicated to the shell. But, it is entirely possible that the embedder can obtain these task runners from a thread pool. * There can only be one Dart VM in the process. The numerous shell interact with one another to manage the VM lifecycle. Once the last shell goes away, the VM does as well and hence all resources associated with the VM are collected. * The shell as a target can now compile and run on Fuchsia. The current content handler has been removed from the Flutter engine source tree and a new implementation has been written that uses the new shell target. * Isolate management has been significantly overhauled. There are no owning references to Dart isolates within the shell. The VM owns the only strong reference to the Dart isolate. The isolate that has window bindings is now called the root isolate. Child isolates can now be created from the root isolate and their bindings and thread configurations are now inherited from the root isolate. * Terminating the shell terminates its root isolates as well as all the isolates spawned by this isolate. This is necessary be shell shutdown is deterministic and the embedder is free to collect the threads on which the isolates execute their tasks (and listen for mircrotasks flushes on). * Launching the root isolate is now significantly overhauled. The shell side (non-owning) reference to an isolate is now a little state machine and illegal state transitions should be impossible (barring construction issues). This is the only way to manage Dart isolates in the shell (the shell does not use the C API is dart_api.h anymore). * Once an isolate is launched, it must be prepared (and hence move to the ready phase) by associating a snapshot with the same. This snapshot can either be a precompiled snapshot, kernel snapshot, script snapshot or source file. Depending on the kind of data specified as a snapshot as well as the capabilities of the VM running in the process, isolate preparation can fail preparation with the right message. * Asset management has been significantly overhauled. All asset resolution goes through an abstract asset resolver interface. An asset manager implements this interface and manages one or more child asset resolvers. These asset resolvers typically resolve assets from directories, ZIP files (legacy FLX assets if provided), APK bundles, FDIO namespaces, etc… * Each launch of the shell requires a separate and fully configured asset resolver. This is necessary because launching isolates for the engine may require resolving snapshots as assets from the asset resolver. Asset resolvers can be shared by multiple launch instances in multiple shells and need to be thread safe. * References to the command line object have been removed from the shell. Instead, the shell only takes a settings object that may be configured from the command line. This makes it easy for embedders and platforms that don’t have a command line (Fuchsia) to configure the shell. Consequently, there is only one spot where the various switches are read from the command line (by the embedder and not the shell) to form the settings object. * All platform now respect the log tag (this was done only by Android till now) and each shell instance have its own log tag. This makes logs from multiple Flutter application in the same process (mainly Fuchsia) more easily decipherable. * The per shell IO task runner now has a new component that is unfortunately named the IOManager. This component manages the IO GrContext (used for asynchronous texture uploads) that cooperates with the GrContext on the GPU task runner associated with the shell. The IOManager is also responsible for flushing tasks that collect Skia objects that reference GPU resources during deterministic shell shutdown. * The embedder now has to be careful to only enable Blink on a single instance of the shell. Launching the legacy text layout and rendering engine multiple times is will trip assertions. The entirety of this runtime has been separated out into a separate object and can be removed in one go when the migration to libtxt is complete. * There is a new test target for the various C++ objects that the shell uses to interact with the Dart VM (the shell no longer use the C API in dart_api.h). This allows engine developers to test VM/Isolate initialization and teardown without having the setup a full shell instance. * There is a new test target for the testing a single shell instances without having to configure and launch an entire VM and associated root isolate. * Mac, Linux & Windows used to have different target that created the flutter_tester referenced by the tool. This has now been converted into a single target that compiles on all platforms. * WeakPointers vended by the fml::WeakPtrFactory(notice the difference between the same class in the fxl namespace) add threading checks on each use. This is enabled by getting rid of the “re-origination” feature of the WeakPtrFactory in the fxl namespace. The side effect of this is that all non-thread safe components have to be created, used and destroyed on the same thread. Numerous thread safety issues were caught by this extra assertion and have now been fixed. * Glossary of components that are only safe on a specific thread (and have the fml variants of the WeakPtrFactory): * Platform Thread: Shell * UI Thread: Engine, RuntimeDelegate, DartIsolate, Animator * GPU Thread: Rasterizer, Surface * IO Thread: IOManager This patch was reviewed in smaller chunks in the following pull requests. All comments from the pulls requests has been incorporated into this patch: * flutter/assets: flutter#4829 * flutter/common: flutter#4830 * flutter/content_handler: flutter#4831 * flutter/flow: flutter#4832 * flutter/fml: flutter#4833 * flutter/lib/snapshot: flutter#4834 * flutter/lib/ui: flutter#4835 * flutter/runtime: flutter#4836 * flutter/shell: flutter#4837 * flutter/synchronization: flutter#4838 * flutter/testing: flutter#4839
The Flutter Engine currently works by initializing a singleton shell instance. This shell has to be created on the platform thread. The shell is responsible for creating the 3 main threads used by Flutter (UI, IO, GPU) as well as initializing the Dart VM. The shell, references to task runners of the main threads as well as all snapshots used for VM initialization are stored in singleton objects. The Flutter shell only creates the threads, rasterizers, contexts, etc. to fully support a single Flutter application. Current support for multiple Flutter applications is achieved by making multiple applications share the same resources (via the platform views mechanism). This scheme has the following limitations: * The shell is a singleton and there is no way to tear it down. Once you run a Flutter application in a process, all resources managed by it will remain referenced till process termination. * The threads on which the shell performs its operations are all singletons. These threads are never torn down and multiple Flutter applications (if present) have to compete with one another on these threads. * Resources referenced by the Dart VM are leaked because the VM isn't shutdown even when there are no more Flutter views. * The shell as a target does not compile on Fuchsia. The Fuchsia content handler uses specific dependencies of the shell to rebuild all the shell dependencies on its own. This leads to differences in frame scheduling, VM setup, service protocol endpoint setup, tracing, etc.. Fuchsia is very much a second class citizen in this world. * Since threads and message loops are managed by the engine, the engine has to know about threading and platform message loop interop on each supported platform. Specific updates in this patch: * The shell is no longer a singleton and the embedder holds the unique reference to the shell. * Shell setup and teardown is deterministic. * Threads are no longer managed by the shell. Instead, the shell is given a task runner configuration by the embedder. * Since the shell does not own its threads, the embedder can control threads and the message loops operating on these threads. The shell is only given references to the task runners that execute tasks on these threads. * The shell only needs task runner references. These references can be to the same task runner. So, if the embedder thinks that a particular Flutter application would not need all the threads, it can pass references to the same task runner. This effectively makes Flutter application run in single threaded mode. There are some places in the shell that make synchronous calls, these sites have been updated to ensure that they don’t deadlock. * The test runner and the headless Dart code runner are now Flutter applications that are effectively single threaded (since they don’t have rendering concerns of big-boy Flutter application). * The embedder has to guarantee that the threads and outlive the shell. It is easy for the embedder to make that guarantee because shell termination is deterministic. * The embedder can create as many shell as it wants. Typically it creates a shell per Flutter application with its own task runner configuration. Most embedders obtain these task runners from threads dedicated to the shell. But, it is entirely possible that the embedder can obtain these task runners from a thread pool. * There can only be one Dart VM in the process. The numerous shell interact with one another to manage the VM lifecycle. Once the last shell goes away, the VM does as well and hence all resources associated with the VM are collected. * The shell as a target can now compile and run on Fuchsia. The current content handler has been removed from the Flutter engine source tree and a new implementation has been written that uses the new shell target. * Isolate management has been significantly overhauled. There are no owning references to Dart isolates within the shell. The VM owns the only strong reference to the Dart isolate. The isolate that has window bindings is now called the root isolate. Child isolates can now be created from the root isolate and their bindings and thread configurations are now inherited from the root isolate. * Terminating the shell terminates its root isolates as well as all the isolates spawned by this isolate. This is necessary be shell shutdown is deterministic and the embedder is free to collect the threads on which the isolates execute their tasks (and listen for mircrotasks flushes on). * Launching the root isolate is now significantly overhauled. The shell side (non-owning) reference to an isolate is now a little state machine and illegal state transitions should be impossible (barring construction issues). This is the only way to manage Dart isolates in the shell (the shell does not use the C API is dart_api.h anymore). * Once an isolate is launched, it must be prepared (and hence move to the ready phase) by associating a snapshot with the same. This snapshot can either be a precompiled snapshot, kernel snapshot, script snapshot or source file. Depending on the kind of data specified as a snapshot as well as the capabilities of the VM running in the process, isolate preparation can fail preparation with the right message. * Asset management has been significantly overhauled. All asset resolution goes through an abstract asset resolver interface. An asset manager implements this interface and manages one or more child asset resolvers. These asset resolvers typically resolve assets from directories, ZIP files (legacy FLX assets if provided), APK bundles, FDIO namespaces, etc… * Each launch of the shell requires a separate and fully configured asset resolver. This is necessary because launching isolates for the engine may require resolving snapshots as assets from the asset resolver. Asset resolvers can be shared by multiple launch instances in multiple shells and need to be thread safe. * References to the command line object have been removed from the shell. Instead, the shell only takes a settings object that may be configured from the command line. This makes it easy for embedders and platforms that don’t have a command line (Fuchsia) to configure the shell. Consequently, there is only one spot where the various switches are read from the command line (by the embedder and not the shell) to form the settings object. * All platform now respect the log tag (this was done only by Android till now) and each shell instance have its own log tag. This makes logs from multiple Flutter application in the same process (mainly Fuchsia) more easily decipherable. * The per shell IO task runner now has a new component that is unfortunately named the IOManager. This component manages the IO GrContext (used for asynchronous texture uploads) that cooperates with the GrContext on the GPU task runner associated with the shell. The IOManager is also responsible for flushing tasks that collect Skia objects that reference GPU resources during deterministic shell shutdown. * The embedder now has to be careful to only enable Blink on a single instance of the shell. Launching the legacy text layout and rendering engine multiple times is will trip assertions. The entirety of this runtime has been separated out into a separate object and can be removed in one go when the migration to libtxt is complete. * There is a new test target for the various C++ objects that the shell uses to interact with the Dart VM (the shell no longer use the C API in dart_api.h). This allows engine developers to test VM/Isolate initialization and teardown without having the setup a full shell instance. * There is a new test target for the testing a single shell instances without having to configure and launch an entire VM and associated root isolate. * Mac, Linux & Windows used to have different target that created the flutter_tester referenced by the tool. This has now been converted into a single target that compiles on all platforms. * WeakPointers vended by the fml::WeakPtrFactory(notice the difference between the same class in the fxl namespace) add threading checks on each use. This is enabled by getting rid of the “re-origination” feature of the WeakPtrFactory in the fxl namespace. The side effect of this is that all non-thread safe components have to be created, used and destroyed on the same thread. Numerous thread safety issues were caught by this extra assertion and have now been fixed. * Glossary of components that are only safe on a specific thread (and have the fml variants of the WeakPtrFactory): * Platform Thread: Shell * UI Thread: Engine, RuntimeDelegate, DartIsolate, Animator * GPU Thread: Rasterizer, Surface * IO Thread: IOManager This patch was reviewed in smaller chunks in the following pull requests. All comments from the pulls requests has been incorporated into this patch: * flutter/assets: flutter#4829 * flutter/common: flutter#4830 * flutter/content_handler: flutter#4831 * flutter/flow: flutter#4832 * flutter/fml: flutter#4833 * flutter/lib/snapshot: flutter#4834 * flutter/lib/ui: flutter#4835 * flutter/runtime: flutter#4836 * flutter/shell: flutter#4837 * flutter/synchronization: flutter#4838 * flutter/testing: flutter#4839
* Support multiple shells in a single process. The Flutter Engine currently works by initializing a singleton shell instance. This shell has to be created on the platform thread. The shell is responsible for creating the 3 main threads used by Flutter (UI, IO, GPU) as well as initializing the Dart VM. The shell, references to task runners of the main threads as well as all snapshots used for VM initialization are stored in singleton objects. The Flutter shell only creates the threads, rasterizers, contexts, etc. to fully support a single Flutter application. Current support for multiple Flutter applications is achieved by making multiple applications share the same resources (via the platform views mechanism). This scheme has the following limitations: * The shell is a singleton and there is no way to tear it down. Once you run a Flutter application in a process, all resources managed by it will remain referenced till process termination. * The threads on which the shell performs its operations are all singletons. These threads are never torn down and multiple Flutter applications (if present) have to compete with one another on these threads. * Resources referenced by the Dart VM are leaked because the VM isn't shutdown even when there are no more Flutter views. * The shell as a target does not compile on Fuchsia. The Fuchsia content handler uses specific dependencies of the shell to rebuild all the shell dependencies on its own. This leads to differences in frame scheduling, VM setup, service protocol endpoint setup, tracing, etc.. Fuchsia is very much a second class citizen in this world. * Since threads and message loops are managed by the engine, the engine has to know about threading and platform message loop interop on each supported platform. Specific updates in this patch: * The shell is no longer a singleton and the embedder holds the unique reference to the shell. * Shell setup and teardown is deterministic. * Threads are no longer managed by the shell. Instead, the shell is given a task runner configuration by the embedder. * Since the shell does not own its threads, the embedder can control threads and the message loops operating on these threads. The shell is only given references to the task runners that execute tasks on these threads. * The shell only needs task runner references. These references can be to the same task runner. So, if the embedder thinks that a particular Flutter application would not need all the threads, it can pass references to the same task runner. This effectively makes Flutter application run in single threaded mode. There are some places in the shell that make synchronous calls, these sites have been updated to ensure that they don’t deadlock. * The test runner and the headless Dart code runner are now Flutter applications that are effectively single threaded (since they don’t have rendering concerns of big-boy Flutter application). * The embedder has to guarantee that the threads and outlive the shell. It is easy for the embedder to make that guarantee because shell termination is deterministic. * The embedder can create as many shell as it wants. Typically it creates a shell per Flutter application with its own task runner configuration. Most embedders obtain these task runners from threads dedicated to the shell. But, it is entirely possible that the embedder can obtain these task runners from a thread pool. * There can only be one Dart VM in the process. The numerous shell interact with one another to manage the VM lifecycle. Once the last shell goes away, the VM does as well and hence all resources associated with the VM are collected. * The shell as a target can now compile and run on Fuchsia. The current content handler has been removed from the Flutter engine source tree and a new implementation has been written that uses the new shell target. * Isolate management has been significantly overhauled. There are no owning references to Dart isolates within the shell. The VM owns the only strong reference to the Dart isolate. The isolate that has window bindings is now called the root isolate. Child isolates can now be created from the root isolate and their bindings and thread configurations are now inherited from the root isolate. * Terminating the shell terminates its root isolates as well as all the isolates spawned by this isolate. This is necessary be shell shutdown is deterministic and the embedder is free to collect the threads on which the isolates execute their tasks (and listen for mircrotasks flushes on). * Launching the root isolate is now significantly overhauled. The shell side (non-owning) reference to an isolate is now a little state machine and illegal state transitions should be impossible (barring construction issues). This is the only way to manage Dart isolates in the shell (the shell does not use the C API is dart_api.h anymore). * Once an isolate is launched, it must be prepared (and hence move to the ready phase) by associating a snapshot with the same. This snapshot can either be a precompiled snapshot, kernel snapshot, script snapshot or source file. Depending on the kind of data specified as a snapshot as well as the capabilities of the VM running in the process, isolate preparation can fail preparation with the right message. * Asset management has been significantly overhauled. All asset resolution goes through an abstract asset resolver interface. An asset manager implements this interface and manages one or more child asset resolvers. These asset resolvers typically resolve assets from directories, ZIP files (legacy FLX assets if provided), APK bundles, FDIO namespaces, etc… * Each launch of the shell requires a separate and fully configured asset resolver. This is necessary because launching isolates for the engine may require resolving snapshots as assets from the asset resolver. Asset resolvers can be shared by multiple launch instances in multiple shells and need to be thread safe. * References to the command line object have been removed from the shell. Instead, the shell only takes a settings object that may be configured from the command line. This makes it easy for embedders and platforms that don’t have a command line (Fuchsia) to configure the shell. Consequently, there is only one spot where the various switches are read from the command line (by the embedder and not the shell) to form the settings object. * All platform now respect the log tag (this was done only by Android till now) and each shell instance have its own log tag. This makes logs from multiple Flutter application in the same process (mainly Fuchsia) more easily decipherable. * The per shell IO task runner now has a new component that is unfortunately named the IOManager. This component manages the IO GrContext (used for asynchronous texture uploads) that cooperates with the GrContext on the GPU task runner associated with the shell. The IOManager is also responsible for flushing tasks that collect Skia objects that reference GPU resources during deterministic shell shutdown. * The embedder now has to be careful to only enable Blink on a single instance of the shell. Launching the legacy text layout and rendering engine multiple times is will trip assertions. The entirety of this runtime has been separated out into a separate object and can be removed in one go when the migration to libtxt is complete. * There is a new test target for the various C++ objects that the shell uses to interact with the Dart VM (the shell no longer use the C API in dart_api.h). This allows engine developers to test VM/Isolate initialization and teardown without having the setup a full shell instance. * There is a new test target for the testing a single shell instances without having to configure and launch an entire VM and associated root isolate. * Mac, Linux & Windows used to have different target that created the flutter_tester referenced by the tool. This has now been converted into a single target that compiles on all platforms. * WeakPointers vended by the fml::WeakPtrFactory(notice the difference between the same class in the fxl namespace) add threading checks on each use. This is enabled by getting rid of the “re-origination” feature of the WeakPtrFactory in the fxl namespace. The side effect of this is that all non-thread safe components have to be created, used and destroyed on the same thread. Numerous thread safety issues were caught by this extra assertion and have now been fixed. * Glossary of components that are only safe on a specific thread (and have the fml variants of the WeakPtrFactory): * Platform Thread: Shell * UI Thread: Engine, RuntimeDelegate, DartIsolate, Animator * GPU Thread: Rasterizer, Surface * IO Thread: IOManager This patch was reviewed in smaller chunks in the following pull requests. All comments from the pulls requests has been incorporated into this patch: * flutter/assets: #4829 * flutter/common: #4830 * flutter/content_handler: #4831 * flutter/flow: #4832 * flutter/fml: #4833 * flutter/lib/snapshot: #4834 * flutter/lib/ui: #4835 * flutter/runtime: #4836 * flutter/shell: #4837 * flutter/synchronization: #4838 * flutter/testing: #4839
Landed in #4932. |
The Flutter Engine currently works by initializing a singleton shell instance. This shell has to be created on the platform thread. The shell is responsible for creating the 3 main threads used by Flutter (UI, IO, GPU) as well as initializing the Dart VM. The shell, references to task runners of the main threads as well as all snapshots used for VM initialization are stored in singleton objects. The Flutter shell only creates the threads, rasterizers, contexts, etc. to fully support a single Flutter application. Current support for multiple Flutter applications is achieved by making multiple applications share the same resources (via the platform views mechanism). This scheme has the following limitations: * The shell is a singleton and there is no way to tear it down. Once you run a Flutter application in a process, all resources managed by it will remain referenced till process termination. * The threads on which the shell performs its operations are all singletons. These threads are never torn down and multiple Flutter applications (if present) have to compete with one another on these threads. * Resources referenced by the Dart VM are leaked because the VM isn't shutdown even when there are no more Flutter views. * The shell as a target does not compile on Fuchsia. The Fuchsia content handler uses specific dependencies of the shell to rebuild all the shell dependencies on its own. This leads to differences in frame scheduling, VM setup, service protocol endpoint setup, tracing, etc.. Fuchsia is very much a second class citizen in this world. * Since threads and message loops are managed by the engine, the engine has to know about threading and platform message loop interop on each supported platform. Specific updates in this patch: * The shell is no longer a singleton and the embedder holds the unique reference to the shell. * Shell setup and teardown is deterministic. * Threads are no longer managed by the shell. Instead, the shell is given a task runner configuration by the embedder. * Since the shell does not own its threads, the embedder can control threads and the message loops operating on these threads. The shell is only given references to the task runners that execute tasks on these threads. * The shell only needs task runner references. These references can be to the same task runner. So, if the embedder thinks that a particular Flutter application would not need all the threads, it can pass references to the same task runner. This effectively makes Flutter application run in single threaded mode. There are some places in the shell that make synchronous calls, these sites have been updated to ensure that they don’t deadlock. * The test runner and the headless Dart code runner are now Flutter applications that are effectively single threaded (since they don’t have rendering concerns of big-boy Flutter application). * The embedder has to guarantee that the threads and outlive the shell. It is easy for the embedder to make that guarantee because shell termination is deterministic. * The embedder can create as many shell as it wants. Typically it creates a shell per Flutter application with its own task runner configuration. Most embedders obtain these task runners from threads dedicated to the shell. But, it is entirely possible that the embedder can obtain these task runners from a thread pool. * There can only be one Dart VM in the process. The numerous shell interact with one another to manage the VM lifecycle. Once the last shell goes away, the VM does as well and hence all resources associated with the VM are collected. * The shell as a target can now compile and run on Fuchsia. The current content handler has been removed from the Flutter engine source tree and a new implementation has been written that uses the new shell target. * Isolate management has been significantly overhauled. There are no owning references to Dart isolates within the shell. The VM owns the only strong reference to the Dart isolate. The isolate that has window bindings is now called the root isolate. Child isolates can now be created from the root isolate and their bindings and thread configurations are now inherited from the root isolate. * Terminating the shell terminates its root isolates as well as all the isolates spawned by this isolate. This is necessary be shell shutdown is deterministic and the embedder is free to collect the threads on which the isolates execute their tasks (and listen for mircrotasks flushes on). * Launching the root isolate is now significantly overhauled. The shell side (non-owning) reference to an isolate is now a little state machine and illegal state transitions should be impossible (barring construction issues). This is the only way to manage Dart isolates in the shell (the shell does not use the C API is dart_api.h anymore). * Once an isolate is launched, it must be prepared (and hence move to the ready phase) by associating a snapshot with the same. This snapshot can either be a precompiled snapshot, kernel snapshot, script snapshot or source file. Depending on the kind of data specified as a snapshot as well as the capabilities of the VM running in the process, isolate preparation can fail preparation with the right message. * Asset management has been significantly overhauled. All asset resolution goes through an abstract asset resolver interface. An asset manager implements this interface and manages one or more child asset resolvers. These asset resolvers typically resolve assets from directories, ZIP files (legacy FLX assets if provided), APK bundles, FDIO namespaces, etc… * Each launch of the shell requires a separate and fully configured asset resolver. This is necessary because launching isolates for the engine may require resolving snapshots as assets from the asset resolver. Asset resolvers can be shared by multiple launch instances in multiple shells and need to be thread safe. * References to the command line object have been removed from the shell. Instead, the shell only takes a settings object that may be configured from the command line. This makes it easy for embedders and platforms that don’t have a command line (Fuchsia) to configure the shell. Consequently, there is only one spot where the various switches are read from the command line (by the embedder and not the shell) to form the settings object. * All platform now respect the log tag (this was done only by Android till now) and each shell instance have its own log tag. This makes logs from multiple Flutter application in the same process (mainly Fuchsia) more easily decipherable. * The per shell IO task runner now has a new component that is unfortunately named the IOManager. This component manages the IO GrContext (used for asynchronous texture uploads) that cooperates with the GrContext on the GPU task runner associated with the shell. The IOManager is also responsible for flushing tasks that collect Skia objects that reference GPU resources during deterministic shell shutdown. * The embedder now has to be careful to only enable Blink on a single instance of the shell. Launching the legacy text layout and rendering engine multiple times is will trip assertions. The entirety of this runtime has been separated out into a separate object and can be removed in one go when the migration to libtxt is complete. * There is a new test target for the various C++ objects that the shell uses to interact with the Dart VM (the shell no longer use the C API in dart_api.h). This allows engine developers to test VM/Isolate initialization and teardown without having the setup a full shell instance. * There is a new test target for the testing a single shell instances without having to configure and launch an entire VM and associated root isolate. * Mac, Linux & Windows used to have different target that created the flutter_tester referenced by the tool. This has now been converted into a single target that compiles on all platforms. * WeakPointers vended by the fml::WeakPtrFactory(notice the difference between the same class in the fxl namespace) add threading checks on each use. This is enabled by getting rid of the “re-origination” feature of the WeakPtrFactory in the fxl namespace. The side effect of this is that all non-thread safe components have to be created, used and destroyed on the same thread. Numerous thread safety issues were caught by this extra assertion and have now been fixed. * Glossary of components that are only safe on a specific thread (and have the fml variants of the WeakPtrFactory): * Platform Thread: Shell * UI Thread: Engine, RuntimeDelegate, DartIsolate, Animator * GPU Thread: Rasterizer, Surface * IO Thread: IOManager This patch was reviewed in smaller chunks in the following pull requests. All comments from the pulls requests has been incorporated into this patch: * flutter/assets: flutter#4829 * flutter/common: flutter#4830 * flutter/content_handler: flutter#4831 * flutter/flow: flutter#4832 * flutter/fml: flutter#4833 * flutter/lib/snapshot: flutter#4834 * flutter/lib/ui: flutter#4835 * flutter/runtime: flutter#4836 * flutter/shell: flutter#4837 * flutter/synchronization: flutter#4838 * flutter/testing: flutter#4839
This changes is part of a large patch for easier review. Try the whole patch in one go by checking out https://github.com/chinmaygarde/flutter_engine/tree/shell directly. This patch contains the following changes: