[samples/ffi] Sample for asynchronous callbacks

Issue: dart-lang/sdk#37022 (comment)

Change-Id: If30d168e6666131b6d96d5885a0dbe32291b1ef9
Cq-Include-Trybots: luci.dart.try:vm-ffi-android-debug-arm-try,vm-ffi-android-debug-arm64-try,app-kernel-linux-debug-x64-try,vm-kernel-linux-debug-ia32-try,vm-kernel-win-debug-x64-try,vm-kernel-win-debug-ia32-try,vm-kernel-precomp-linux-debug-x64-try,vm-dartkb-linux-release-x64-abi-try,vm-kernel-precomp-android-release-arm64-try,vm-kernel-asan-linux-release-x64-try,vm-kernel-linux-release-simarm-try,vm-kernel-linux-release-simarm64-try,vm-kernel-precomp-android-release-arm_x64-try,vm-kernel-precomp-obfuscate-linux-release-x64-try,dart-sdk-linux-try,analyzer-analysis-server-linux-try,analyzer-linux-release-try,front-end-linux-release-x64-try,vm-kernel-precomp-win-release-x64-try
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/134704
Reviewed-by: Martin Kustermann <kustermann@google.com>

runtime/bin/BUILD.gn

@@ -1120,6 +1120,7 @@ shared_library("ffi_test_dynamic_library") {
     cflags = [ "-fPIC" ]
   }
   if (is_win) {
+    # TODO(dartbug.com/40579): This wrongly links in dart.exe on precompiled.
     libs = [ "dart.lib" ]
     abs_root_out_dir = rebase_path(root_out_dir)
     ldflags = [ "/LIBPATH:$abs_root_out_dir" ]
@@ -1153,6 +1154,7 @@ shared_library("ffi_test_functions") {
     cflags = [ "-fPIC" ]
   }
   if (is_win) {
+    # TODO(dartbug.com/40579): This wrongly links in dart.exe on precompiled.
     libs = [ "dart.lib" ]
     abs_root_out_dir = rebase_path(root_out_dir)
     ldflags = [ "/LIBPATH:$abs_root_out_dir" ]

runtime/bin/ffi_test/ffi_test_functions_vmspecific.cc

@@ -12,21 +12,26 @@
 #include "platform/globals.h"
 #if defined(HOST_OS_WINDOWS)
 #include <psapi.h>
+#include <windows.h>
 #else
 #include <unistd.h>
+#endif
 
 // Only OK to use here because this is test code.
 #include <condition_variable>  // NOLINT(build/c++11)
 #include <functional>          // NOLINT(build/c++11)
 #include <mutex>               // NOLINT(build/c++11)
+#include <queue>               // NOLINT(build/c++11)
 #include <thread>              // NOLINT(build/c++11)
-#endif
 
-#include <setjmp.h>
-#include <signal.h>
+#include <setjmp.h>  // NOLINT
+#include <signal.h>  // NOLINT
 #include <iostream>
 #include <limits>
 
+// TODO(dartbug.com/40579): This requires static linking to either link
+// dart.exe or dart_precompiled_runtime.exe on Windows.
+// The sample currently fails on Windows in AOT mode.
 #include "include/dart_api.h"
 #include "include/dart_native_api.h"
 
@@ -264,4 +269,195 @@ DART_EXPORT intptr_t TestCallbackWrongIsolate(void (*fn)()) {
 
 #endif  // defined(TARGET_OS_LINUX)
 
+////////////////////////////////////////////////////////////////////////////////
+// Functions for async callbacks example.
+//
+// sample_async_callback.dart
+
+void Fatal(char const* file, int line, char const* error) {
+  printf("FATAL %s:%i\n", file, line);
+  printf("%s\n", error);
+  Dart_DumpNativeStackTrace(NULL);
+  Dart_PrepareToAbort();
+  abort();
+}
+
+#define FATAL(error) Fatal(__FILE__, __LINE__, error)
+
+void SleepOnAnyOS(intptr_t seconds) {
+#if defined(HOST_OS_WINDOWS)
+  Sleep(1000 * seconds);
+#else
+  sleep(seconds);
+#endif
+}
+
+intptr_t (*my_callback_blocking_fp_)(intptr_t);
+Dart_Port my_callback_blocking_send_port_;
+
+void (*my_callback_non_blocking_fp_)(intptr_t);
+Dart_Port my_callback_non_blocking_send_port_;
+
+typedef std::function<void()> Work;
+
+// Notify Dart through a port that the C lib has pending async callbacks.
+//
+// Expects heap allocated `work` so delete can be called on it.
+//
+// The `send_port` should be from the isolate which registered the callback.
+void NotifyDart(Dart_Port send_port, const Work* work) {
+  const intptr_t work_addr = reinterpret_cast<intptr_t>(work);
+  printf("C   :  Posting message (port: %" Px64 ", work: %" Px ").\n",
+         send_port, work_addr);
+
+  Dart_CObject dart_object;
+  dart_object.type = Dart_CObject_kInt64;
+  dart_object.value.as_int64 = work_addr;
+
+  const bool result = Dart_PostCObject(send_port, &dart_object);
+  if (!result) {
+    FATAL("C   :  Posting message to port failed.");
+  }
+}
+
+// Do a callback to Dart in a blocking way, being interested in the result.
+//
+// Dart returns `a + 3`.
+intptr_t MyCallbackBlocking(intptr_t a) {
+  std::mutex mutex;
+  std::unique_lock<std::mutex> lock(mutex);
+  intptr_t result;
+  auto callback = my_callback_blocking_fp_;  // Define storage duration.
+  std::condition_variable cv;
+  bool notified = false;
+  const Work work = [a, &result, callback, &cv, &notified]() {
+    result = callback(a);
+    printf("C Da:     Notify result ready.\n");
+    notified = true;
+    cv.notify_one();
+  };
+  const Work* work_ptr = new Work(work);  // Copy to heap.
+  NotifyDart(my_callback_blocking_send_port_, work_ptr);
+  printf("C   :  Waiting for result.\n");
+  while (!notified) {
+    cv.wait(lock);
+  }
+  printf("C   :  Received result.\n");
+  return result;
+}
+
+// Do a callback to Dart in a non-blocking way.
+//
+// Dart sums all numbers posted to it.
+void MyCallbackNonBlocking(intptr_t a) {
+  auto callback = my_callback_non_blocking_fp_;  // Define storage duration.
+  const Work work = [a, callback]() { callback(a); };
+  // Copy to heap to make it outlive the function scope.
+  const Work* work_ptr = new Work(work);
+  NotifyDart(my_callback_non_blocking_send_port_, work_ptr);
+}
+
+// Simulated work for Thread #1.
+//
+// Simulates heavy work with sleeps.
+void Work1() {
+  printf("C T1: Work1 Start.\n");
+  SleepOnAnyOS(1);
+  const intptr_t val1 = 3;
+  printf("C T1: MyCallbackBlocking(%" Pd ").\n", val1);
+  const intptr_t val2 = MyCallbackBlocking(val1);  // val2 = 6.
+  printf("C T1: MyCallbackBlocking returned %" Pd ".\n", val2);
+  SleepOnAnyOS(1);
+  const intptr_t val3 = val2 - 1;  // val3 = 5.
+  printf("C T1: MyCallbackNonBlocking(%" Pd ").\n", val3);
+  MyCallbackNonBlocking(val3);  // Post 5 to Dart.
+  printf("C T1: Work1 Done.\n");
+}
+
+// Simulated work for Thread #2.
+//
+// Simulates lighter work, no sleeps.
+void Work2() {
+  printf("C T2: Work2 Start.\n");
+  const intptr_t val1 = 5;
+  printf("C T2: MyCallbackNonBlocking(%" Pd ").\n", val1);
+  MyCallbackNonBlocking(val1);  // Post 5 to Dart.
+  const intptr_t val2 = 1;
+  printf("C T2: MyCallbackBlocking(%" Pd ").\n", val2);
+  const intptr_t val3 = MyCallbackBlocking(val2);  // val3 = 4.
+  printf("C T2: MyCallbackBlocking returned %" Pd ".\n", val3);
+  printf("C T2: MyCallbackNonBlocking(%" Pd ").\n", val3);
+  MyCallbackNonBlocking(val3);  // Post 4 to Dart.
+  printf("C T2: Work2 Done.\n");
+}
+
+// Simulator that simulates concurrent work with multiple threads.
+class SimulateWork {
+ public:
+  static void StartWorkSimulator() {
+    running_work_simulator_ = new SimulateWork();
+    running_work_simulator_->Start();
+  }
+
+  static void StopWorkSimulator() {
+    running_work_simulator_->Stop();
+    delete running_work_simulator_;
+    running_work_simulator_ = nullptr;
+  }
+
+ private:
+  static SimulateWork* running_work_simulator_;
+
+  void Start() {
+    printf("C Da:  Starting SimulateWork.\n");
+    printf("C Da:   Starting worker threads.\n");
+    thread1 = new std::thread(Work1);
+    thread2 = new std::thread(Work2);
+    printf("C Da:  Started SimulateWork.\n");
+  }
+
+  void Stop() {
+    printf("C Da:  Stopping SimulateWork.\n");
+    printf("C Da:   Waiting for worker threads to finish.\n");
+    thread1->join();
+    thread2->join();
+    delete thread1;
+    delete thread2;
+    printf("C Da:  Stopped SimulateWork.\n");
+  }
+
+  std::thread* thread1;
+  std::thread* thread2;
+};
+SimulateWork* SimulateWork::running_work_simulator_ = 0;
+
+DART_EXPORT void RegisterMyCallbackBlocking(Dart_Port send_port,
+                                            intptr_t (*callback1)(intptr_t)) {
+  my_callback_blocking_fp_ = callback1;
+  my_callback_blocking_send_port_ = send_port;
+}
+
+DART_EXPORT void RegisterMyCallbackNonBlocking(Dart_Port send_port,
+                                               void (*callback)(intptr_t)) {
+  my_callback_non_blocking_fp_ = callback;
+  my_callback_non_blocking_send_port_ = send_port;
+}
+
+DART_EXPORT void StartWorkSimulator() {
+  SimulateWork::StartWorkSimulator();
+}
+
+DART_EXPORT void StopWorkSimulator() {
+  SimulateWork::StopWorkSimulator();
+}
+
+DART_EXPORT void ExecuteCallback(Work* work_ptr) {
+  printf("C Da:    ExecuteCallback(%" Pp ").\n",
+         reinterpret_cast<intptr_t>(work_ptr));
+  const Work work = *work_ptr;
+  work();
+  delete work_ptr;
+  printf("C Da:    ExecuteCallback done.\n");
+}
+
 }  // namespace dart

samples/ffi/async/async_test.dart

@@ -0,0 +1,13 @@
+// Copyright (c) 2020, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+//
+// This file exercises the sample files so that they are tested.
+//
+// SharedObjects=ffi_test_dynamic_library ffi_test_functions
+
+import 'sample_async_callback.dart' as sample0;
+
+main() {
+  sample0.main();
+}

samples/ffi/async/sample_async_callback.dart

@@ -0,0 +1,109 @@
+// Copyright (c) 2020, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+//
+// Sample showing how to do async callbacks by telling the Dart isolate to
+// yields its execution thread to C so it can perform the callbacks on the
+// main Dart thread.
+//
+// TODO(dartbug.com/37022): Update this when we get real async callbacks.
+// TODO(dartbug.com/40564): On Windows DLL is wrongly linked against dart.exe
+// instead of dart_precompiled_runtime.exe
+
+import 'dart:ffi';
+import 'dart:isolate';
+
+import 'package:expect/expect.dart';
+
+import '../dylib_utils.dart';
+
+int globalResult = 0;
+int numCallbacks1 = 0;
+int numCallbacks2 = 0;
+
+main() async {
+  print("Dart = Dart mutator thread executing Dart.");
+  print("C Da = Dart mutator thread executing C.");
+  print("C T1 = Some C thread executing C.");
+  print("C T2 = Some C thread executing C.");
+  print("C    = C T1 or C T2.");
+  print("Dart: Setup.");
+  final interactiveCppRequests = ReceivePort()..listen(requestExecuteCallback);
+
+  final int nativePort = interactiveCppRequests.sendPort.nativePort;
+  registerCallback1(nativePort, callback1FP);
+  registerCallback2(nativePort, callback2FP);
+  print("Dart: Tell C to start worker threads.");
+  startWorkSimulator();
+
+  // We need to yield control in order to be able to receive messages.
+  while (numCallbacks2 < 3) {
+    print("Dart: Yielding (able to receive messages on port).");
+    await asyncSleep(500);
+  }
+  print("Dart: Received expected number of callbacks.");
+
+  Expect.equals(2, numCallbacks1);
+  Expect.equals(3, numCallbacks2);
+  Expect.equals(14, globalResult);
+
+  print("Dart: Tell C to stop worker threads.");
+  stopWorkSimulator();
+  interactiveCppRequests.close();
+  print("Dart: Done.");
+}
+
+int callback1(int a) {
+  print("Dart:     callback1($a).");
+  numCallbacks1++;
+  return a + 3;
+}
+
+void callback2(int a) {
+  print("Dart:     callback2($a).");
+  globalResult += a;
+  numCallbacks2++;
+}
+
+void requestExecuteCallback(dynamic message) {
+  final int work_address = message;
+  final work = Pointer<Work>.fromAddress(work_address);
+  print("Dart:   Calling into C to execute callback ($work).");
+  executeCallback(work);
+  print("Dart:   Done with callback.");
+}
+
+final callback1FP = Pointer.fromFunction<IntPtr Function(IntPtr)>(callback1, 0);
+
+final callback2FP = Pointer.fromFunction<Void Function(IntPtr)>(callback2);
+
+final dl = dlopenPlatformSpecific("ffi_test_functions");
+
+final registerCallback1 = dl.lookupFunction<
+        Void Function(Int64 sendPort,
+            Pointer<NativeFunction<IntPtr Function(IntPtr)>> functionPointer),
+        void Function(int sendPort,
+            Pointer<NativeFunction<IntPtr Function(IntPtr)>> functionPointer)>(
+    'RegisterMyCallbackBlocking');
+
+final registerCallback2 = dl.lookupFunction<
+        Void Function(Int64 sendPort,
+            Pointer<NativeFunction<Void Function(IntPtr)>> functionPointer),
+        void Function(int sendPort,
+            Pointer<NativeFunction<Void Function(IntPtr)>> functionPointer)>(
+    'RegisterMyCallbackNonBlocking');
+
+final startWorkSimulator =
+    dl.lookupFunction<Void Function(), void Function()>('StartWorkSimulator');
+
+final stopWorkSimulator =
+    dl.lookupFunction<Void Function(), void Function()>('StopWorkSimulator');
+
+final executeCallback = dl.lookupFunction<Void Function(Pointer<Work>),
+    void Function(Pointer<Work>)>('ExecuteCallback');
+
+class Work extends Struct {}
+
+Future asyncSleep(int ms) {
+  return new Future.delayed(Duration(milliseconds: ms));
+}

samples/samples.status

@@ -14,15 +14,17 @@ sample_extension/test/sample_extension_app_snapshot_test: SkipByDesign # This te
 [ $compiler == dart2js && $runtime == none ]
 *: Fail, Pass # TODO(ahe): Triage these tests.
 
+[ $compiler == dartkp && $system == windows ]
+ffi/async/async_test: Skip # dartbug.com/40564 dartbug.com/40579
+
 [ $compiler == none && $mode == debug && $runtime == vm && $system == windows ]
 sample_extension/test/sample_extension_app_snapshot_test: Pass, RuntimeError # Issue 28842
 
 [ $compiler == none && $runtime == vm && $system == fuchsia ]
 *: Skip # Not yet triaged.
 
 [ $arch == simarm || $arch == simarm64 ]
-ffi/resource_management/resource_management_test: SkipByDesign
-ffi/samples_test: SkipByDesign # FFI skips, see ffi.status
+ffi/*: SkipByDesign # FFI skips, see ffi.status
 
 [ $arch != x64 || $compiler != dartk || $system != linux || $hot_reload || $hot_reload_rollback ]
 ffi/sqlite/test/sqlite_test: SkipByDesign # FFI not supported or libsqlite3.so not available.