Add a simple Job queue in default port. #1685

jiangzidong · 2017-03-24T05:05:07Z

Job queue is the basis of Promise.
as the spec says

A promise p is fulfilled if p.then(f, r) will immediately enqueue a Job to call the function f.
A promise p is rejected if p.then(f, r) will immediately enqueue a Job to call the function r.

Each port should implement their own job queue.
Job queue is very similar to the event loop of node.js and iot.js.

After introducing the job queue, when the sync part of the js code are executed by vm, it should check the queue, and do the pending jobs in FIFO order.

This patch only implemented the simplest queue, which actually cannot handle the true async callback.
e.g.

var  a = new Promise (function(f, r){
  setTimeout(f, 100); // if there is a binding api setTimeout, it will fail in current queue
})

LaszloLango · 2017-03-24T06:36:21Z

jerry-core/jerry-port.h

 double jerry_port_get_current_time (void);

+#ifndef CONFIG_DISABLE_ES2015_PROMISE_BUILTIN
+#include "ecma-jobqueue.h"


I think including this is not a good idea. IMHO we shouldn't make internal parts public. It would be great to separate the private and public parts more clearly.

I see, the external can expose interface to internal, the reverse can't.
I find the definition of jerry_property_descriptor_t in jerryscript.h is same as ecma_property_descriptor_t in ecma-globals.h. So I think I can use the similar method in jerry-port.h: define the same struct with different name.

martijnthe · 2017-03-24T06:39:27Z

I wonder if it makes sense to make this more generic (and extensible w/o having to change ecma-jobqueue.h to add new types).

I suspect that each type will have its own callback/handler, so we could remove the explicit type field and use a function pointer instead:

typedef void (*ecma_job_handler_t)(ecma_job_promise_reaction_job_t *job_p, void *user_data_p);

typedef struct
{
  ecma_job_handler_t handler; /** < callback that will execute the job */
  void *user_data_p;
} ecma_job_t;

Furthermore, I'd probably try to avoid exposing "internals" (i.e. ecma_job_t) in jerry....h files.
I'd rather see something like this:

// jerryscript.h

typedef void (*jerry_job_handler_t)(void *user_data_p);

/** Enqueue an async callback on the internal job queue */
void jerry_job_enqueue (jerry_job_handler_t *jerry_job_handler_p, void *user_data_p);

Note I added void *user_data_p into ecma_job_t so that the type definition of ecma_job_t can be internal to ecma-jobqueue.c.

The downside is you probably have to do 2 allocations (1 for the ecma_job_t and 1 to store the user data). There are ways to just have one allocation by having a ecma_job_t * ecma_job_allocate_with_extra_data(size_t extra_data_sz) and forward-declaring ecma_job_t. But this complicates the API, not sure if it's worth it.

LaszloLango · 2017-03-24T06:41:07Z

I like the way how you trying to do this. Jobs must depend on the actual port. Nice work.

martijnthe · 2017-03-24T06:46:56Z

targets/default/jerry-port-default-jobqueue.c

+      return;
+    }
+
+    ecma_job_process (job_p);


ecma_job_process should probably be exposed in jerry-port.h somehow, to avoid reaching into internals.

Hmm, this is the first time the port needs to call back into JrS, I think?

Is there a convention to indicate in a port header that a function declaration is there to indicate the port can/needs to call it? (I'm used to adding extern as a hint, but don't know if that's a widespread convention or not.)

Seems passing the function pointer can solve this problem.

If the job_p is defined like you suggest

typedef struct { ecma_job_handler_t handler; /** < callback that will execute the job */ void *user_data_p; } ecma_job_t;

When get the job_p from the queue, directly call job_p->handler(job_p)

So there is no ecma_job_process in internal, and we need to implement all process-functions for different types of jobs in ecma-jobqueue.c.

martijnthe · 2017-03-24T06:52:11Z

targets/default/jerry-port-default-jobqueue.c

+    }
+
+    ecma_job_process (job_p);
+  }


Who/what is responsible for freeing the job_p? (Right now it's being leaked, I think.)

Related; I guess if there's a "job allocator" API (like I described vaguely in the other comment) and all jobs are allocated by JrS, it can also take responsibility for freeing them after executing the callback.

In my designs, they should be freed in the end of ecma_job_process, in ecma_job_process_promise_reaction_job or ecma_job_process_promise_thenable_job.

Because in the PR, no one allocate job yet, so i didn't write the "release" code

zherczeg · 2017-03-24T07:31:22Z

jerry-core/ecma/operations/ecma-jobqueue.h

+ */
+typedef struct
+{
+  ecma_job_type_t type; /**< specific type of the job */


enums are compiler specific, sometimes int, sometimes unsigned char. I would prefer to use an uint8_t here.

zherczeg · 2017-03-24T07:34:12Z

Are jobs are always resolved in-order?

zherczeg · 2017-03-24T07:35:52Z

targets/default/jerry-port-default-jobqueue.c

+  jerry_port_queueitem_t *tail_p; /**< point to the tail item of the queue*/
+} jerry_port_jobqueue_t;
+
+jerry_port_jobqueue_t queue;


Static writable declarations are not allowed in JerryScript, you need to move this into jcontext.h.

can I include jcontext.h in port?

Hmm, because the queue's implementation heavily depends on the actual port. If the OS already have the event queue, you can directly use that. Here I just provide the simplest one in default port.
So I don't think it is suitable to be in jcontext.h. What do you think?

I haven't noticed that this is port specific. Leave it then.

Probably add static here in any case?

Yes, please add a static at least.

jiangzidong · 2017-03-24T07:46:31Z

@zherczeg

Are jobs are always resolved in-order?

I think the "resolve" here means "process job", then answer is YES.

The PendingJob records from a single Job Queue are always initiated in FIFO order. This specification does not define the order in which multiple Job Queues are serviced

jiangzidong · 2017-03-24T08:46:22Z

Another commit submitted.

use function handler to replace the type member of ecma_job_t
define jerry_job_t in jerry-port.h, which is used by port file. so that the port dont include ecma-xxx.h
jobqueue_run will directly call job_p->handler (job_p) instead of calling the ecma_job_process.

zherczeg · 2017-03-24T09:41:45Z

targets/default/jerry-port-default-jobqueue.c

+
+
+
+#ifndef CONFIG_DISABLE_ES2015_PROMISE_BUILTIN


Extra newlines.

zherczeg · 2017-03-24T09:42:07Z

jerry-core/jerry-port.h

+#ifndef CONFIG_DISABLE_ES2015_PROMISE_BUILTIN
+
+
+typedef struct jerry_job_t jerry_job_t;


Extra newlines.

zherczeg · 2017-03-24T09:45:50Z

targets/default/jerry-port-default-jobqueue.c

+  jerry_port_queueitem_t *tail_p; /**< point to the tail item of the queue*/
+} jerry_port_jobqueue_t;
+
+jerry_port_jobqueue_t queue;


I haven't noticed that this is port specific. Leave it then.

zherczeg · 2017-03-24T09:48:57Z

jerry-core/jerry-port.h

+
+void jerry_port_jobqueue_init (void);
+void jerry_port_jobqueue_enqueue (jerry_job_t *job_p);
+void jerry_port_jobqueue_run (void);


As far as I see there is no need for exporting jerry_port_jobqueue_init and jerry_port_jobqueue_run functions. I confused later because I expected that ports must share them. The only function needed is jerry_port_jobqueue_enqueue and we expect that the callback is eventually called by the port. The how is the own business of the port.

Alternative idea:

Make jerry_port_jobqueue_enqueue expect two arguments: a callback and a job pointer. The port needs a queue item represenation anyway and adding two values shouldn't be a bigger issue than adding one.

about the Alternative idea:

The callback is already in the jerry_job_t, what is the benefit that we separate them?

about jerry_port_jobqueue_init and jerry_port_jobqueue_run:

You are right! Those two functions are called by the port, and jerry-core will never call them directly. My mistake

Benefit: you can drop the jerry_job_t type. This would simplify a lot of definitions later.

I prefer to keep the handler in the jerry_job_t, because it establish a connection between the callback and job (job actually is callback's arguments) in the jerry internal. Otherwise, the connection only exists in the port's queue item.

zherczeg · 2017-03-24T09:51:38Z

jerry-core/jerry-port.h

+
+struct jerry_job_t
+{
+  jerry_job_handler_t handler; /**< the handler funtion for the job */


Do we need a jerry_job_handler_t type? We could simply write it here:

void (*handler) (struct jerry_job_t *);

I don't really like the typedef above.

IMO, typedef is cleaner, and used in many place like jerryscript.h and jmem.h

zherczeg · 2017-03-24T12:34:24Z

jerry-core/ecma/operations/ecma-jobqueue.h

+struct ecma_job_t
+{
+  ecma_job_handler_t handler; /**< the handler funtion for the job */
+};


Actually these are my issues with the current approach. An ecma_job_t is defined here, which is basically a jerry_job_t. Furthermore both definitions require a circular definitions, and that is never a good practice. The structures below also follows some class in C programming model.

My suggestion is: keep the callback at jerry_port.h/ The enqueue get the callback and a user pointer. Since the callback is not stored in the job, ecma_job_promise_reaction_job_t and ecma_job_promise_thenable_job_t do not need to depend on anything. We will use different callbacks for reaction and thenable (what a strange word) so there will be no confusion. I think we need less type casts overall.

Then the callback in jerryport.h should be

typedef void (*jerry_job_handler_t) (uintptr_t); void jerry_port_jobqueue_enqueue (jerry_job_handler_t, uintptr_t);

and in every callback body, we need to cast the uintptr_t to some specific job_t (e.g. ecma_job_promise_reaction_job_t)

Am I right?

Yes, except I would use void* instead of uintptr_t. Casting would be needed anyway since we have multiple job types.

But at least we don't need casting a struct* to void*.

Just a question: a job does not have a return value? What happens with exceptions?

You remind me that the job_handler should have return value, and if exception happens, perform implementation defined unhandled exception processing.. In the simple queue, I will stop the queue running. I will update the patch soon

zherczeg · 2017-03-24T13:26:24Z

What is your plan for engine shut-down? I suspect we should empty the queue and not allow inserting more items. Or what should happen?

The multiple queues part is also unclear for me. Do we need multiple queues for a single JerryScript instance?

jiangzidong · 2017-03-24T13:53:47Z

I think one typical flow after introducing jobqueue/promise will be

1, jerry_init
2, jerry_parse
3, queue_init (just make sure it is before jerry_run)
4, jerry_run (in this step, jerry may enqueue some jobs)
5, queue_run (it is a loop, because each job in the queue may also enqueue more jobs)
6, jerry_cleanup

For now, only one queue (PromiseQueue) in Jerry. If we plan to support module & import, there will be another queue. ES2015 only defined those 2 queues, and I also think they can share one physical queue, because This specification does not define the order in which multiple Job Queues are serviced and it only make sure each queue should be FIFO

jiangzidong · 2017-03-24T14:50:16Z

updated the patch, the job handler should return the exception if it happens.

martijnthe · 2017-03-25T08:57:43Z

targets/default/jerry-port-default-jobqueue.c

+{
+  jerry_value_t ret;
+
+  while (1)


I'm wondering if it makes sense to put this loop into an ecma_... file and let it call out to the port for:

Getting the next item (you already have this: jerry_port_jobqueue_dequeue())

Handling the case when there are no items in the queue ("If all Job Queues are empty, the result is implementation defined.") => maybe add jerry_port_jobqueue_handle_queue_empty()?

Handling an error result ("If result is an abrupt completion, perform implementation defined unhandled exception processing.") => maybe add jerry_port_jobqueue_handle_error()?

I think the loop should be in port file.
When people port the jerry-engine into a embedded project, the project/OS may already have its own queue mechanism/event loop, for example, the libtuv for iotjs. Then the loop in jerry might conflict the loop in the outer project/OS

while (true)

martijnthe · 2017-03-25T09:09:28Z

jerry-core/jerry-port.h

+
+typedef uint32_t (*jerry_job_handler_t) (void *);
+
+void jerry_port_jobqueue_enqueue (jerry_job_handler_t handler, void *job_p);


👍 Nice, this way any binding that needs to execute something asynchronously (for example setTimeout()) can use this to schedule the callback. In other words, the JobQueue feature is also useful for other (non-ES2015 Promise dependent) use cases.

Because of this, I think it makes sense to make a separate CONFIG_DISABLE_ES2015_JOBQUEUE feature flag.

I think it is too early to set the seperate CONFIG_DISABLE_ES2015_JOBQUEUE, the reasons are as follows:

for now, only promise will use jobqueue. Enabling only one of "JOBQUEUE" and "PROMISE" does not make much sense.

in the future, when we plan to support module (which also use jobqueue), we will enable jobqueue by #if !defined(CONFIG_DISABLE_PROMISE) || !defined(CONFIG_DISABLE_MODULE)

will setTimeout use the jobqueue? it is out of jerry-core's scope, because setTimeout is a external api. The binding code can directly use the jobqueue in the port no matter whether job queue is enabled in jerry-core. (That is another reason why I think the loop should not be in jerry-core)

Yup, you're right. I've thought about this a bit more and I'm starting to doubt whether my comment here makes sense. The source of the ES6 job queue events/jobs is from things internal to JerryScript (for now only Promise), while for something like setTimeout(), the event source is the native/host system, which would put an event into the (existing) native event loop.

martijnthe · 2017-03-25T09:20:45Z

ES2015 only defined those 2 queues, and I also think they can share one physical queue, because This specification does not define the order in which multiple Job Queues are serviced and it only make sure each queue should be FIFO.

Yeah, that is also what I understand from the spec. I think because uses of JobQueues by the ES6 spec itself don't have any prioritization requirements, I think the current jerry_port_jobqueue_enqueue() interface is sufficient. If a binding built on top of this does require different priorities between jobs, this can be solved entirely inside the port implementation. In short: 👍

martijnthe · 2017-03-25T09:38:54Z

As far as I see there is no need for exporting jerry_port_jobqueue_init and jerry_port_jobqueue_run functions. I confused later because I expected that ports must share them. The only function needed is jerry_port_jobqueue_enqueue and we expect that the callback is eventually called by the port. The how is the own business of the port.

@zherczeg Hmm.. Did you see that ES6 introduced a section "ECMAScript Initialization()" which talks about the first time "NextJob" is called? http://www.ecma-international.org/ecma-262/6.0/#sec-ecmascript-initialization

I wonder if it makes sense to add a public helper to jerryscript.h (i.e. void jerry_init_and_run_loop(jerry_init_flag_t flags, const jerry_value_t main_func_val)?) that takes these steps in the right order -- including queue init + run (pretty much what @jiangzidong outlined in #1685 (comment)).

jiangzidong · 2017-03-25T15:50:32Z

About the ECMAScript Initialization, we dont have to implement it with jobqueue and enqueue the ScriptEvaluationJob in the first place. Instead, we can directly call the jerry_parse/jerry_run first, then enter the loop to process the jobs/events (both iotjs and nodejs are using the above mechanism). I agree with @zherczeg that only jerry_port_jobqueue_enqueue should be exported and leave init/run for the port.

At least, I suggest that we only export jerry_port_jobqueue_enqueue in this first version, cause it's straightforward and with less change needed. Then, when we have the promise (the application for jobqueue), we can submit following patches to optimize/enhance jobqueue.

martijnthe · 2017-03-26T13:36:13Z

I think the loop should be in port file. When people port the jerry-engine into a embedded project, the project/OS may already have its own queue mechanism/event loop, for example, the libtuv for iotjs. Then the loop in jerry might conflict the loop in the outer project/OS

Ah, you're right. Putting the loop into JrS would force everyone to change any existing event loop, which is not nice.

At least, I suggest that we only export jerry_port_jobqueue_enqueue in this first version, cause it's straightforward and with less change needed. Then, when we have the promise (the application for jobqueue), we can submit following patches to optimize/enhance jobqueue.

SGTM.

zherczeg

The core is pretty good now. Several style fixes needed though.

zherczeg · 2017-03-27T13:19:21Z

targets/default/jerry-port-default-jobqueue.c

+struct jerry_port_queueitem_t
+{
+  jerry_port_queueitem_t *next_p; /**< point to next item */
+  jerry_job_handler_t handler; /**< the hanlder for the job*/


/**< the handler for the job */

zherczeg · 2017-03-27T13:19:52Z

targets/default/jerry-port-default-jobqueue.c

+typedef struct
+{
+  jerry_port_queueitem_t *head_p; /**< point to the head item of the queue */
+  jerry_port_queueitem_t *tail_p; /**< point to the tail item of the queue*/


/**< points to the head item of the queue */
/**< points to the tail item of the queue */

zherczeg · 2017-03-27T13:20:20Z

targets/default/jerry-port-default-jobqueue.c

+  jerry_port_queueitem_t *tail_p; /**< point to the tail item of the queue*/
+} jerry_port_jobqueue_t;
+
+jerry_port_jobqueue_t queue;


Yes, please add a static at least.

zherczeg · 2017-03-27T13:21:59Z

targets/default/jerry-port-default-jobqueue.c

+
+    queue.head_p = item_p;
+    item_p->next_p = NULL;
+    queue.tail_p = queue.head_p;


queue.tail_p = item_p;

zherczeg · 2017-03-27T13:22:38Z

targets/default/jerry-port-default-jobqueue.c

+{
+  jerry_value_t ret;
+
+  while (1)


while (true)

zherczeg · 2017-03-27T13:23:31Z

targets/default/jerry-port-default-jobqueue.c

+#include "jerry-port-default.h"
+#include "jrt.h"
+#include "jmem.h"
+#include "jerryscript.h"


Should be alphabetic order.

Thanks for reminding me. I just knew the rule.

zherczeg · 2017-03-27T13:24:01Z

jerry-core/ecma/operations/ecma-jobqueue.c

+#include "ecma-globals.h"
+#include "jerry-port.h"
+#include "ecma-jobqueue.h"
+#include "ecma-helpers.h"


Should be in alphabetic order.

jiangzidong · 2017-03-27T13:57:17Z

targets/default/jerry-port-default-jobqueue.c

+    if (jerry_value_has_error_flag (ret))
+    {
+      return ret;
+    }


if no error flag, we also need to release the ret value. Will add in the updated patch soon

jiangzidong · 2017-03-27T14:05:28Z

@zherczeg updated.

Job queue (event loop) is the basis of Promise. Each port should implement their own job queue. JerryScript-DCO-1.0-Signed-off-by: Zidong Jiang zidong.jiang@intel.com

martijnthe · 2017-03-27T15:17:10Z

targets/default/jerry-port-default-jobqueue.c

+
+    if (jerry_value_has_error_flag (ret))
+    {
+      return ret;


Reading the NextJob section again (http://www.ecma-international.org/ecma-262/6.0/#sec-nextjob-result) I'm not sure whether the loop (recursion in the spec) should be stopped. It doesn't say that it returns after an error result. I guess you could argue that whether or not to return could fall under the implementation specific part.

That said, I think it's more useful to not return (keep looping) and instead call out to another port function to handle the error result, for example by using jerry_port_console() to print out the error message. I think something like that is what most people will do in actual projects.

I think it makes sense to expose a void jerry_port_handle_uncaught_error(jerry_value_t error) into jerry-port.h. Any user binding code that uses async callbacks can then also use the same interface to deal with uncaught errors.

I think it's more useful to not return (keep looping) and instead call out to another port function to handle the error result

In Node.js, the uncaught error will stop the loop

setTimeout(function(){console.log(x)}, 100); //error: no reference setTimeout(function(){console.log("will not show this")}, 200);

I know that the following code will run correctly

Promise.resolve(1).then(function(){console.log(x}); setTimeout(function(){console.log("WILL run here"), 100};

Because although function(){console.log(x} will throw error, it is not the result of NextJob, it is the step 7 of http://www.ecma-international.org/ecma-262/6.0/#sec-promisereactionjob

expose a handler into jerry-port.h

I doubt it. The caller of the handler is only the port-specific queue_run function, not the jerry-core.

The default port's queue is designed for main-unix.c as a simple demo, and it is only a simplest queue which cannot even handle real-async event. So in my design, the uncaught error will stop the queue, then developers can write their own error-process function in main-unix.c (usually print the error message). I wonder if it is necessary to increase the complexity of the default queue.

In Node.js, the uncaught error will stop the loop

Ah, interesting. Chrome's behavior is different, it does actually print the "will not show this" log.

OK, let's just leave it as-is.

zherczeg

LGTM. Great patch!

LaszloLango

LGTM

jiangzidong mentioned this pull request Mar 24, 2017

ES6 Promise #1675

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LaszloLango added the ES2015 Related to ES2015 features label Mar 24, 2017

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Add a simple Job queue in default port.

bff41cf

Job queue (event loop) is the basis of Promise. Each port should implement their own job queue. JerryScript-DCO-1.0-Signed-off-by: Zidong Jiang zidong.jiang@intel.com

martijnthe reviewed Mar 27, 2017

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zherczeg approved these changes Mar 28, 2017

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LaszloLango approved these changes Mar 28, 2017

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jiangzidong merged commit 16d5d6f into jerryscript-project:master Mar 28, 2017

martijnthe mentioned this pull request May 5, 2017

Is the JobQueue Port API a good abstraction? #1799

Closed

		#ifndef CONFIG_DISABLE_ES2015_PROMISE_BUILTIN


		typedef struct jerry_job_t jerry_job_t;


		typedef uint32_t (jerry_job_handler_t) (void );

		void jerry_port_jobqueue_enqueue (jerry_job_handler_t handler, void *job_p);

Add a simple Job queue in default port. #1685

Add a simple Job queue in default port. #1685

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zherczeg commented Mar 24, 2017

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