gecko-dev/dom/workers/WorkerThread.cpp

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9.0 KiB
C++
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/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* vim: set ts=8 sts=2 et sw=2 tw=80: */
/* This Source Code Form is subject to the terms of the Mozilla Public
* License, v. 2.0. If a copy of the MPL was not distributed with this
* file, You can obtain one at http://mozilla.org/MPL/2.0/. */
#include "WorkerThread.h"
#include "mozilla/Assertions.h"
#include "mozilla/ipc/BackgroundChild.h"
Bug 1382922 - Refactor event queue to allow multiple implementations (r=erahm) This patch refactors the nsThread event queue to clean it up and to make it easier to restructure. The fundamental concepts are as follows: Each nsThread will have a pointer to a refcounted SynchronizedEventQueue. A SynchronizedEQ takes care of doing the locking and condition variable work when posting and popping events. For the actual storage of events, it delegates to an AbstractEventQueue data structure. It keeps a UniquePtr to the AbstractEventQueue that it uses for storage. Both SynchronizedEQ and AbstractEventQueue are abstract classes. There is only one concrete implementation of SynchronizedEQ in this patch, which is called ThreadEventQueue. ThreadEventQueue uses locks and condition variables to post and pop events the same way nsThread does. It also encapsulates the functionality that DOM workers need to implement their special event loops (PushEventQueue and PopEventQueue). In later Quantum DOM work, I plan to have another SynchronizedEQ implementation for the main thread, called SchedulerEventQueue. It will have special code for the cooperatively scheduling threads in Quantum DOM. There are two concrete implementations of AbstractEventQueue in this patch: EventQueue and PrioritizedEventQueue. EventQueue replaces the old nsEventQueue. The other AbstractEventQueue implementation is PrioritizedEventQueue, which uses multiple queues for different event priorities. The final major piece here is ThreadEventTarget, which splits some of the code for posting events out of nsThread. Eventually, my plan is for multiple cooperatively scheduled nsThreads to be able to share a ThreadEventTarget. In this patch, though, each nsThread has its own ThreadEventTarget. The class's purpose is just to collect some related code together. One final note: I tried to avoid virtual dispatch overhead as much as possible. Calls to SynchronizedEQ methods do use virtual dispatch, since I plan to use different implementations for different threads with Quantum DOM. But all the calls to EventQueue methods should be non-virtual. Although the methods are declared virtual, all the classes used are final and the concrete classes involved should all be known through templatization. MozReview-Commit-ID: 9Evtr9oIJvx
2017-06-21 05:42:13 +03:00
#include "EventQueue.h"
#include "mozilla/ThreadEventQueue.h"
#include "nsIThreadInternal.h"
#include "WorkerPrivate.h"
#include "WorkerRunnable.h"
#ifdef DEBUG
#include "nsThreadManager.h"
#endif
namespace mozilla {
using namespace ipc;
namespace dom {
namespace {
// The C stack size. We use the same stack size on all platforms for
// consistency.
const uint32_t kWorkerStackSize = 256 * sizeof(size_t) * 1024;
} // namespace
WorkerThreadFriendKey::WorkerThreadFriendKey()
{
MOZ_COUNT_CTOR(WorkerThreadFriendKey);
}
WorkerThreadFriendKey::~WorkerThreadFriendKey()
{
MOZ_COUNT_DTOR(WorkerThreadFriendKey);
}
class WorkerThread::Observer final
: public nsIThreadObserver
{
WorkerPrivate* mWorkerPrivate;
public:
explicit Observer(WorkerPrivate* aWorkerPrivate)
: mWorkerPrivate(aWorkerPrivate)
{
MOZ_ASSERT(aWorkerPrivate);
aWorkerPrivate->AssertIsOnWorkerThread();
}
NS_DECL_THREADSAFE_ISUPPORTS
private:
~Observer()
{
mWorkerPrivate->AssertIsOnWorkerThread();
}
NS_DECL_NSITHREADOBSERVER
};
WorkerThread::WorkerThread()
: nsThread(MakeNotNull<ThreadEventQueue<mozilla::EventQueue>*>(
MakeUnique<mozilla::EventQueue>()),
Bug 1382922 - Refactor event queue to allow multiple implementations (r=erahm) This patch refactors the nsThread event queue to clean it up and to make it easier to restructure. The fundamental concepts are as follows: Each nsThread will have a pointer to a refcounted SynchronizedEventQueue. A SynchronizedEQ takes care of doing the locking and condition variable work when posting and popping events. For the actual storage of events, it delegates to an AbstractEventQueue data structure. It keeps a UniquePtr to the AbstractEventQueue that it uses for storage. Both SynchronizedEQ and AbstractEventQueue are abstract classes. There is only one concrete implementation of SynchronizedEQ in this patch, which is called ThreadEventQueue. ThreadEventQueue uses locks and condition variables to post and pop events the same way nsThread does. It also encapsulates the functionality that DOM workers need to implement their special event loops (PushEventQueue and PopEventQueue). In later Quantum DOM work, I plan to have another SynchronizedEQ implementation for the main thread, called SchedulerEventQueue. It will have special code for the cooperatively scheduling threads in Quantum DOM. There are two concrete implementations of AbstractEventQueue in this patch: EventQueue and PrioritizedEventQueue. EventQueue replaces the old nsEventQueue. The other AbstractEventQueue implementation is PrioritizedEventQueue, which uses multiple queues for different event priorities. The final major piece here is ThreadEventTarget, which splits some of the code for posting events out of nsThread. Eventually, my plan is for multiple cooperatively scheduled nsThreads to be able to share a ThreadEventTarget. In this patch, though, each nsThread has its own ThreadEventTarget. The class's purpose is just to collect some related code together. One final note: I tried to avoid virtual dispatch overhead as much as possible. Calls to SynchronizedEQ methods do use virtual dispatch, since I plan to use different implementations for different threads with Quantum DOM. But all the calls to EventQueue methods should be non-virtual. Although the methods are declared virtual, all the classes used are final and the concrete classes involved should all be known through templatization. MozReview-Commit-ID: 9Evtr9oIJvx
2017-06-21 05:42:13 +03:00
nsThread::NOT_MAIN_THREAD,
kWorkerStackSize)
, mLock("WorkerThread::mLock")
, mWorkerPrivateCondVar(mLock, "WorkerThread::mWorkerPrivateCondVar")
, mWorkerPrivate(nullptr)
, mOtherThreadsDispatchingViaEventTarget(0)
#ifdef DEBUG
, mAcceptingNonWorkerRunnables(true)
#endif
{
}
WorkerThread::~WorkerThread()
{
MOZ_ASSERT(!mWorkerPrivate);
MOZ_ASSERT(!mOtherThreadsDispatchingViaEventTarget);
MOZ_ASSERT(mAcceptingNonWorkerRunnables);
}
// static
already_AddRefed<WorkerThread>
WorkerThread::Create(const WorkerThreadFriendKey& /* aKey */)
{
Bug 1207245 - part 6 - rename nsRefPtr<T> to RefPtr<T>; r=ehsan; a=Tomcat The bulk of this commit was generated with a script, executed at the top level of a typical source code checkout. The only non-machine-generated part was modifying MFBT's moz.build to reflect the new naming. CLOSED TREE makes big refactorings like this a piece of cake. # The main substitution. find . -name '*.cpp' -o -name '*.cc' -o -name '*.h' -o -name '*.mm' -o -name '*.idl'| \ xargs perl -p -i -e ' s/nsRefPtr\.h/RefPtr\.h/g; # handle includes s/nsRefPtr ?</RefPtr</g; # handle declarations and variables ' # Handle a special friend declaration in gfx/layers/AtomicRefCountedWithFinalize.h. perl -p -i -e 's/::nsRefPtr;/::RefPtr;/' gfx/layers/AtomicRefCountedWithFinalize.h # Handle nsRefPtr.h itself, a couple places that define constructors # from nsRefPtr, and code generators specially. We do this here, rather # than indiscriminantly s/nsRefPtr/RefPtr/, because that would rename # things like nsRefPtrHashtable. perl -p -i -e 's/nsRefPtr/RefPtr/g' \ mfbt/nsRefPtr.h \ xpcom/glue/nsCOMPtr.h \ xpcom/base/OwningNonNull.h \ ipc/ipdl/ipdl/lower.py \ ipc/ipdl/ipdl/builtin.py \ dom/bindings/Codegen.py \ python/lldbutils/lldbutils/utils.py # In our indiscriminate substitution above, we renamed # nsRefPtrGetterAddRefs, the class behind getter_AddRefs. Fix that up. find . -name '*.cpp' -o -name '*.h' -o -name '*.idl' | \ xargs perl -p -i -e 's/nsRefPtrGetterAddRefs/RefPtrGetterAddRefs/g' if [ -d .git ]; then git mv mfbt/nsRefPtr.h mfbt/RefPtr.h else hg mv mfbt/nsRefPtr.h mfbt/RefPtr.h fi --HG-- rename : mfbt/nsRefPtr.h => mfbt/RefPtr.h
2015-10-18 08:24:48 +03:00
RefPtr<WorkerThread> thread = new WorkerThread();
Bug 1431184 - Register DOM Worker threads with the profiler for their entire lifetime, not just for the ranges during which they're running a worker script. r=froydnj Our Web Worker code uses a thread pool where a single OS thread can be reused for different worker scripts during its lifetime. Before this patch, we only registered these threads with the profiler for the duration that they're running a worker script. So the same OS thread could be registered with the profiler during multiple disjoint time ranges, and we would expect the profiler to treat those different registrations as different conceptual threads. This had multiple advantages: - The "thread name" of the conceptual thread can include the script URL: "DOM Worker <scriptURL>". This allowed you to create thread filter which match a part of the URL, so you had the option of profiling just the worker threads you were interested in. - We wouldn't waste time sampling a worker thread while it's idle and has no script. But it also had disadvantages: - The profiler platform doesn't actually know how to deal with different "conceptual threads" that share the same OS thread. This lead to surprising breakage in different places. For example, the contents in the profiler buffer are marked with ThreadId entries which use the OS thread id. - What we show in the profiler UI didn't not match reality, and might be confusing to some people. I don't think the advantages are large enough to warrant teaching the rest of the profiler platform to deal with conceptual threads. So this change makes us stop doing the special thing and just register the OS threads for their entire duration. MozReview-Commit-ID: 82RtlRlwy3Y --HG-- extra : rebase_source : 101e144f17718ea8f05e8bef8200b8ed41ee854e
2018-01-25 02:20:27 +03:00
if (NS_FAILED(thread->Init(NS_LITERAL_CSTRING("DOM Worker")))) {
NS_WARNING("Failed to create new thread!");
return nullptr;
}
return thread.forget();
}
void
WorkerThread::SetWorker(const WorkerThreadFriendKey& /* aKey */,
WorkerPrivate* aWorkerPrivate)
{
MOZ_ASSERT(PR_GetCurrentThread() == mThread);
if (aWorkerPrivate) {
{
MutexAutoLock lock(mLock);
MOZ_ASSERT(!mWorkerPrivate);
MOZ_ASSERT(mAcceptingNonWorkerRunnables);
mWorkerPrivate = aWorkerPrivate;
#ifdef DEBUG
mAcceptingNonWorkerRunnables = false;
#endif
}
mObserver = new Observer(aWorkerPrivate);
MOZ_ALWAYS_SUCCEEDS(AddObserver(mObserver));
} else {
MOZ_ALWAYS_SUCCEEDS(RemoveObserver(mObserver));
mObserver = nullptr;
{
MutexAutoLock lock(mLock);
MOZ_ASSERT(mWorkerPrivate);
MOZ_ASSERT(!mAcceptingNonWorkerRunnables);
MOZ_ASSERT(!mOtherThreadsDispatchingViaEventTarget,
"XPCOM Dispatch hapenning at the same time our thread is "
"being unset! This should not be possible!");
while (mOtherThreadsDispatchingViaEventTarget) {
mWorkerPrivateCondVar.Wait();
}
#ifdef DEBUG
mAcceptingNonWorkerRunnables = true;
#endif
mWorkerPrivate = nullptr;
}
}
}
nsresult
WorkerThread::DispatchPrimaryRunnable(const WorkerThreadFriendKey& /* aKey */,
already_AddRefed<nsIRunnable> aRunnable)
{
nsCOMPtr<nsIRunnable> runnable(aRunnable);
#ifdef DEBUG
MOZ_ASSERT(PR_GetCurrentThread() != mThread);
MOZ_ASSERT(runnable);
{
MutexAutoLock lock(mLock);
MOZ_ASSERT(!mWorkerPrivate);
MOZ_ASSERT(mAcceptingNonWorkerRunnables);
}
#endif
nsresult rv = nsThread::Dispatch(runnable.forget(), NS_DISPATCH_NORMAL);
if (NS_WARN_IF(NS_FAILED(rv))) {
return rv;
}
return NS_OK;
}
nsresult
WorkerThread::DispatchAnyThread(const WorkerThreadFriendKey& /* aKey */,
already_AddRefed<WorkerRunnable> aWorkerRunnable)
{
// May be called on any thread!
#ifdef DEBUG
{
const bool onWorkerThread = PR_GetCurrentThread() == mThread;
{
MutexAutoLock lock(mLock);
MOZ_ASSERT(mWorkerPrivate);
MOZ_ASSERT(!mAcceptingNonWorkerRunnables);
if (onWorkerThread) {
mWorkerPrivate->AssertIsOnWorkerThread();
}
}
}
#endif
nsCOMPtr<nsIRunnable> runnable(aWorkerRunnable);
nsresult rv = nsThread::Dispatch(runnable.forget(), NS_DISPATCH_NORMAL);
if (NS_WARN_IF(NS_FAILED(rv))) {
return rv;
}
// We don't need to notify the worker's condition variable here because we're
// being called from worker-controlled code and it will make sure to wake up
// the worker thread if needed.
return NS_OK;
}
NS_IMETHODIMP
WorkerThread::DispatchFromScript(nsIRunnable* aRunnable, uint32_t aFlags)
{
nsCOMPtr<nsIRunnable> runnable(aRunnable);
return Dispatch(runnable.forget(), aFlags);
}
NS_IMETHODIMP
WorkerThread::Dispatch(already_AddRefed<nsIRunnable> aRunnable, uint32_t aFlags)
{
// May be called on any thread!
nsCOMPtr<nsIRunnable> runnable(aRunnable); // in case we exit early
// Workers only support asynchronous dispatch.
if (NS_WARN_IF(aFlags != NS_DISPATCH_NORMAL)) {
return NS_ERROR_UNEXPECTED;
}
const bool onWorkerThread = PR_GetCurrentThread() == mThread;
#ifdef DEBUG
if (runnable && !onWorkerThread) {
nsCOMPtr<nsICancelableRunnable> cancelable = do_QueryInterface(runnable);
{
MutexAutoLock lock(mLock);
// Only enforce cancelable runnables after we've started the worker loop.
if (!mAcceptingNonWorkerRunnables) {
MOZ_ASSERT(cancelable,
"Only nsICancelableRunnable may be dispatched to a worker!");
}
}
}
#endif
WorkerPrivate* workerPrivate = nullptr;
if (onWorkerThread) {
// No need to lock here because it is only modified on this thread.
MOZ_ASSERT(mWorkerPrivate);
mWorkerPrivate->AssertIsOnWorkerThread();
workerPrivate = mWorkerPrivate;
} else {
MutexAutoLock lock(mLock);
MOZ_ASSERT(mOtherThreadsDispatchingViaEventTarget < UINT32_MAX);
if (mWorkerPrivate) {
workerPrivate = mWorkerPrivate;
// Incrementing this counter will make the worker thread sleep if it
// somehow tries to unset mWorkerPrivate while we're using it.
mOtherThreadsDispatchingViaEventTarget++;
}
}
nsresult rv;
if (runnable && onWorkerThread) {
Bug 1207245 - part 6 - rename nsRefPtr<T> to RefPtr<T>; r=ehsan; a=Tomcat The bulk of this commit was generated with a script, executed at the top level of a typical source code checkout. The only non-machine-generated part was modifying MFBT's moz.build to reflect the new naming. CLOSED TREE makes big refactorings like this a piece of cake. # The main substitution. find . -name '*.cpp' -o -name '*.cc' -o -name '*.h' -o -name '*.mm' -o -name '*.idl'| \ xargs perl -p -i -e ' s/nsRefPtr\.h/RefPtr\.h/g; # handle includes s/nsRefPtr ?</RefPtr</g; # handle declarations and variables ' # Handle a special friend declaration in gfx/layers/AtomicRefCountedWithFinalize.h. perl -p -i -e 's/::nsRefPtr;/::RefPtr;/' gfx/layers/AtomicRefCountedWithFinalize.h # Handle nsRefPtr.h itself, a couple places that define constructors # from nsRefPtr, and code generators specially. We do this here, rather # than indiscriminantly s/nsRefPtr/RefPtr/, because that would rename # things like nsRefPtrHashtable. perl -p -i -e 's/nsRefPtr/RefPtr/g' \ mfbt/nsRefPtr.h \ xpcom/glue/nsCOMPtr.h \ xpcom/base/OwningNonNull.h \ ipc/ipdl/ipdl/lower.py \ ipc/ipdl/ipdl/builtin.py \ dom/bindings/Codegen.py \ python/lldbutils/lldbutils/utils.py # In our indiscriminate substitution above, we renamed # nsRefPtrGetterAddRefs, the class behind getter_AddRefs. Fix that up. find . -name '*.cpp' -o -name '*.h' -o -name '*.idl' | \ xargs perl -p -i -e 's/nsRefPtrGetterAddRefs/RefPtrGetterAddRefs/g' if [ -d .git ]; then git mv mfbt/nsRefPtr.h mfbt/RefPtr.h else hg mv mfbt/nsRefPtr.h mfbt/RefPtr.h fi --HG-- rename : mfbt/nsRefPtr.h => mfbt/RefPtr.h
2015-10-18 08:24:48 +03:00
RefPtr<WorkerRunnable> workerRunnable = workerPrivate->MaybeWrapAsWorkerRunnable(runnable.forget());
rv = nsThread::Dispatch(workerRunnable.forget(), NS_DISPATCH_NORMAL);
} else {
rv = nsThread::Dispatch(runnable.forget(), NS_DISPATCH_NORMAL);
}
if (!onWorkerThread && workerPrivate) {
// We need to wake the worker thread if we're not already on the right
// thread and the dispatch succeeded.
if (NS_SUCCEEDED(rv)) {
MutexAutoLock workerLock(workerPrivate->mMutex);
workerPrivate->mCondVar.Notify();
}
// Now unset our waiting flag.
{
MutexAutoLock lock(mLock);
MOZ_ASSERT(mOtherThreadsDispatchingViaEventTarget);
if (!--mOtherThreadsDispatchingViaEventTarget) {
mWorkerPrivateCondVar.Notify();
}
}
}
if (NS_WARN_IF(NS_FAILED(rv))) {
return rv;
}
return NS_OK;
}
NS_IMETHODIMP
WorkerThread::DelayedDispatch(already_AddRefed<nsIRunnable>, uint32_t)
{
return NS_ERROR_NOT_IMPLEMENTED;
}
uint32_t
WorkerThread::RecursionDepth(const WorkerThreadFriendKey& /* aKey */) const
{
MOZ_ASSERT(PR_GetCurrentThread() == mThread);
return mNestedEventLoopDepth;
}
NS_IMPL_ISUPPORTS(WorkerThread::Observer, nsIThreadObserver)
NS_IMETHODIMP
WorkerThread::Observer::OnDispatchedEvent()
{
MOZ_CRASH("OnDispatchedEvent() should never be called!");
}
NS_IMETHODIMP
WorkerThread::Observer::OnProcessNextEvent(nsIThreadInternal* /* aThread */,
Bug 1179909: Refactor stable state handling. r=smaug This is motivated by three separate but related problems: 1. Our concept of recursion depth is broken for things that run from AfterProcessNextEvent observers (e.g. Promises). We decrement the recursionDepth counter before firing observers, so a Promise callback running at the lowest event loop depth has a recursion depth of 0 (whereas a regular nsIRunnable would be 1). This is a problem because it's impossible to distinguish a Promise running after a sync XHR's onreadystatechange handler from a top-level event (since the former runs with depth 2 - 1 = 1, and the latter runs with just 1). 2. The nsIThreadObserver mechanism that is used by a lot of code to run "after" the current event is a poor fit for anything that runs script. First, the order the observers fire in is the order they were added, not anything fixed by spec. Additionally, running script can cause the event loop to spin, which is a big source of pain here (bholley has some nasty bug caused by this). 3. We run Promises from different points in the code for workers and main thread. The latter runs from XPConnect's nsIThreadObserver callbacks, while the former runs from a hardcoded call to run Promises in the worker event loop. What workers do is particularly problematic because it means we can't get the right recursion depth no matter what we do to nsThread. The solve this, this patch does the following: 1. Consolidate some handling of microtasks and all handling of stable state from appshell and WorkerPrivate into CycleCollectedJSRuntime. 2. Make the recursionDepth counter only available to CycleCollectedJSRuntime (and its consumers) and remove it from the nsIThreadInternal and nsIThreadObserver APIs. 3. Adjust the recursionDepth counter so that microtasks run with the recursionDepth of the task they are associated with. 4. Introduce the concept of metastable state to replace appshell's RunBeforeNextEvent. Metastable state is reached after every microtask or task is completed. This provides the semantics that bent and I want for IndexedDB, where transactions autocommit at the end of a microtask and do not "spill" from one microtask into a subsequent microtask. This differs from appshell's RunBeforeNextEvent in two ways: a) It fires between microtasks, which was the motivation for starting this. b) It no longer ensures that we're at the same event loop depth in the native event queue. bent decided we don't care about this. 5. Reorder stable state to happen after microtasks such as Promises, per HTML. Right now we call the regular thread observers, including appshell, before the main thread observer (XPConnect), so stable state tasks happen before microtasks.
2015-08-11 16:10:46 +03:00
bool aMayWait)
{
mWorkerPrivate->AssertIsOnWorkerThread();
// If the PBackground child is not created yet, then we must permit
// blocking event processing to support
// BackgroundChild::GetOrCreateCreateForCurrentThread(). If this occurs
// then we are spinning on the event queue at the start of
// PrimaryWorkerRunnable::Run() and don't want to process the event in
// mWorkerPrivate yet.
if (aMayWait) {
MOZ_ASSERT(CycleCollectedJSContext::Get()->RecursionDepth() == 2);
MOZ_ASSERT(!BackgroundChild::GetForCurrentThread());
return NS_OK;
}
Bug 1179909: Refactor stable state handling. r=smaug This is motivated by three separate but related problems: 1. Our concept of recursion depth is broken for things that run from AfterProcessNextEvent observers (e.g. Promises). We decrement the recursionDepth counter before firing observers, so a Promise callback running at the lowest event loop depth has a recursion depth of 0 (whereas a regular nsIRunnable would be 1). This is a problem because it's impossible to distinguish a Promise running after a sync XHR's onreadystatechange handler from a top-level event (since the former runs with depth 2 - 1 = 1, and the latter runs with just 1). 2. The nsIThreadObserver mechanism that is used by a lot of code to run "after" the current event is a poor fit for anything that runs script. First, the order the observers fire in is the order they were added, not anything fixed by spec. Additionally, running script can cause the event loop to spin, which is a big source of pain here (bholley has some nasty bug caused by this). 3. We run Promises from different points in the code for workers and main thread. The latter runs from XPConnect's nsIThreadObserver callbacks, while the former runs from a hardcoded call to run Promises in the worker event loop. What workers do is particularly problematic because it means we can't get the right recursion depth no matter what we do to nsThread. The solve this, this patch does the following: 1. Consolidate some handling of microtasks and all handling of stable state from appshell and WorkerPrivate into CycleCollectedJSRuntime. 2. Make the recursionDepth counter only available to CycleCollectedJSRuntime (and its consumers) and remove it from the nsIThreadInternal and nsIThreadObserver APIs. 3. Adjust the recursionDepth counter so that microtasks run with the recursionDepth of the task they are associated with. 4. Introduce the concept of metastable state to replace appshell's RunBeforeNextEvent. Metastable state is reached after every microtask or task is completed. This provides the semantics that bent and I want for IndexedDB, where transactions autocommit at the end of a microtask and do not "spill" from one microtask into a subsequent microtask. This differs from appshell's RunBeforeNextEvent in two ways: a) It fires between microtasks, which was the motivation for starting this. b) It no longer ensures that we're at the same event loop depth in the native event queue. bent decided we don't care about this. 5. Reorder stable state to happen after microtasks such as Promises, per HTML. Right now we call the regular thread observers, including appshell, before the main thread observer (XPConnect), so stable state tasks happen before microtasks.
2015-08-11 16:10:46 +03:00
mWorkerPrivate->OnProcessNextEvent();
return NS_OK;
}
NS_IMETHODIMP
WorkerThread::Observer::AfterProcessNextEvent(nsIThreadInternal* /* aThread */,
bool /* aEventWasProcessed */)
{
mWorkerPrivate->AssertIsOnWorkerThread();
Bug 1179909: Refactor stable state handling. r=smaug This is motivated by three separate but related problems: 1. Our concept of recursion depth is broken for things that run from AfterProcessNextEvent observers (e.g. Promises). We decrement the recursionDepth counter before firing observers, so a Promise callback running at the lowest event loop depth has a recursion depth of 0 (whereas a regular nsIRunnable would be 1). This is a problem because it's impossible to distinguish a Promise running after a sync XHR's onreadystatechange handler from a top-level event (since the former runs with depth 2 - 1 = 1, and the latter runs with just 1). 2. The nsIThreadObserver mechanism that is used by a lot of code to run "after" the current event is a poor fit for anything that runs script. First, the order the observers fire in is the order they were added, not anything fixed by spec. Additionally, running script can cause the event loop to spin, which is a big source of pain here (bholley has some nasty bug caused by this). 3. We run Promises from different points in the code for workers and main thread. The latter runs from XPConnect's nsIThreadObserver callbacks, while the former runs from a hardcoded call to run Promises in the worker event loop. What workers do is particularly problematic because it means we can't get the right recursion depth no matter what we do to nsThread. The solve this, this patch does the following: 1. Consolidate some handling of microtasks and all handling of stable state from appshell and WorkerPrivate into CycleCollectedJSRuntime. 2. Make the recursionDepth counter only available to CycleCollectedJSRuntime (and its consumers) and remove it from the nsIThreadInternal and nsIThreadObserver APIs. 3. Adjust the recursionDepth counter so that microtasks run with the recursionDepth of the task they are associated with. 4. Introduce the concept of metastable state to replace appshell's RunBeforeNextEvent. Metastable state is reached after every microtask or task is completed. This provides the semantics that bent and I want for IndexedDB, where transactions autocommit at the end of a microtask and do not "spill" from one microtask into a subsequent microtask. This differs from appshell's RunBeforeNextEvent in two ways: a) It fires between microtasks, which was the motivation for starting this. b) It no longer ensures that we're at the same event loop depth in the native event queue. bent decided we don't care about this. 5. Reorder stable state to happen after microtasks such as Promises, per HTML. Right now we call the regular thread observers, including appshell, before the main thread observer (XPConnect), so stable state tasks happen before microtasks.
2015-08-11 16:10:46 +03:00
mWorkerPrivate->AfterProcessNextEvent();
return NS_OK;
}
} // namespace dom
} // namespace mozilla