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Bug 1289378 - Fix inter-locking in PDMFactory+GMPDecoderModule - r=jya
Say PDMFactory::EnsureInit() runs on the main thread (effectively locking it) and then tries to lock sMonitor; if another thread was also running EnsureInit() and locked sMonitor, it will dead-lock when trying to sync- dispatch the GMPDecoderModule creation to the main thread. This can be fixed by ensuring that the actual PDMFactory instance creation is always done on the main thread (and that we don't hold sMonitor before dispatching to the main thread.) Note that we can now simplify GMPDecoderModule::Init and assert we are already on the main thread. MozReview-Commit-ID: 8xHpoymw6po --HG-- extra : rebase_source : aabc1f4768aebdd16873bbc1afdd1679d90aed6f
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@ -29,6 +29,7 @@
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#include "mozilla/ClearOnShutdown.h"
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#include "mozilla/SharedThreadPool.h"
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#include "mozilla/StaticPtr.h"
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#include "mozilla/SyncRunnable.h"
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#include "mozilla/TaskQueue.h"
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#include "MediaInfo.h"
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@ -87,17 +88,31 @@ PDMFactory::~PDMFactory()
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void
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PDMFactory::EnsureInit() const
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{
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StaticMutexAutoLock mon(sMonitor);
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if (!sInstance) {
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sInstance = new PDMFactoryImpl();
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{
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StaticMutexAutoLock mon(sMonitor);
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if (sInstance) {
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// Quick exit if we already have an instance.
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return;
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}
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if (NS_IsMainThread()) {
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// On the main thread and holding the lock -> Create instance.
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sInstance = new PDMFactoryImpl();
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ClearOnShutdown(&sInstance);
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} else {
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nsCOMPtr<nsIRunnable> runnable =
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NS_NewRunnableFunction([]() { ClearOnShutdown(&sInstance); });
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NS_DispatchToMainThread(runnable);
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return;
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}
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}
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// Not on the main thread -> Sync-dispatch creation to main thread.
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nsCOMPtr<nsIThread> mainThread = do_GetMainThread();
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nsCOMPtr<nsIRunnable> runnable =
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NS_NewRunnableFunction([]() {
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StaticMutexAutoLock mon(sMonitor);
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if (!sInstance) {
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sInstance = new PDMFactoryImpl();
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ClearOnShutdown(&sInstance);
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}
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});
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SyncRunnable::DispatchToThread(mainThread, runnable);
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}
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already_AddRefed<MediaDataDecoder>
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@ -13,7 +13,6 @@
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#include "mozIGeckoMediaPluginService.h"
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#include "nsServiceManagerUtils.h"
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#include "mozilla/StaticMutex.h"
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#include "mozilla/SyncRunnable.h"
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#include "gmp-audio-decode.h"
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#include "gmp-video-decode.h"
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#ifdef XP_WIN
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@ -169,13 +168,7 @@ GMPDecoderModule::UpdateUsableCodecs()
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void
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GMPDecoderModule::Init()
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{
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if (!NS_IsMainThread()) {
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nsCOMPtr<nsIThread> mainThread = do_GetMainThread();
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nsCOMPtr<nsIRunnable> runnable =
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NS_NewRunnableFunction([]() { Init(); });
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SyncRunnable::DispatchToThread(mainThread, runnable);
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return;
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}
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MOZ_ASSERT(NS_IsMainThread());
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// GMPService::HasPluginForAPI is main thread only, so to implement
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// SupportsMimeType() we build a table of the codecs which each whitelisted
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// GMP has and update it when any GMPs are removed or added at runtime.
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