1 files changed, 35 insertions, 1 deletions
diff --git a/ipc/chromium/src/mojo/core/ports/port.h b/ipc/chromium/src/mojo/core/ports/port.h
index 44529ddb6f..78fe0109b8 100644
--- a/ipc/chromium/src/mojo/core/ports/port.h
+++ b/ipc/chromium/src/mojo/core/ports/port.h
@@ -18,6 +18,18 @@
 #include "mozilla/RefPtr.h"
 #include "nsISupportsImpl.h"
 
+#ifdef MOZ_TSAN
+// In TSAN builds, a single static mutex is used for all ports, rather than
+// per-port mutexes, to avoid overloading the maximum 64 concurrently-held locks
+// limit of its deadlock detector when sending messages with a large number of
+// attached ports.
+#  define MOZ_USE_SINGLETON_PORT_MUTEX 1
+#endif
+
+#ifdef MOZ_USE_SINGLETON_PORT_MUTEX
+#  include "mozilla/StaticMutex.h"
+#endif
+
 namespace mojo {
 namespace core {
 namespace ports {
@@ -28,20 +40,38 @@ namespace detail {
 
 // Ports cannot use mozilla::Mutex, as the acquires-before relationships handled
 // by PortLocker can overload the debug-only deadlock detector.
-class MOZ_CAPABILITY("mutex") PortMutex : private ::mozilla::detail::MutexImpl {
+class MOZ_CAPABILITY("mutex") PortMutex
+#ifndef MOZ_USE_SINGLETON_PORT_MUTEX
+    : private ::mozilla::detail::MutexImpl
+#endif
+{
  public:
   void AssertCurrentThreadOwns() const MOZ_ASSERT_CAPABILITY(this) {
 #ifdef DEBUG
     MOZ_ASSERT(mOwningThread == PR_GetCurrentThread());
 #endif
+#ifdef MOZ_USE_SINGLETON_PORT_MUTEX
+    sSingleton.AssertCurrentThreadOwns();
+#endif
   }
 
  private:
   // PortMutex should only be locked/unlocked via PortLocker
   friend class ::mojo::core::ports::PortLocker;
 
+#ifdef MOZ_USE_SINGLETON_PORT_MUTEX
+  // If the singleton mutex is in use, it must be locked before calling `Lock()`
+  // on any port, and must only be unlocked after calling `Unlock()` on every
+  // locked port.
+  static ::mozilla::StaticMutex sSingleton;
+#endif
+
   void Lock() MOZ_CAPABILITY_ACQUIRE() {
+#ifdef MOZ_USE_SINGLETON_PORT_MUTEX
+    sSingleton.AssertCurrentThreadOwns();
+#else
     ::mozilla::detail::MutexImpl::lock();
+#endif
 #ifdef DEBUG
     mOwningThread = PR_GetCurrentThread();
 #endif
@@ -51,7 +81,11 @@ class MOZ_CAPABILITY("mutex") PortMutex : private ::mozilla::detail::MutexImpl {
     MOZ_ASSERT(mOwningThread == PR_GetCurrentThread());
     mOwningThread = nullptr;
 #endif
+#ifdef MOZ_USE_SINGLETON_PORT_MUTEX
+    sSingleton.AssertCurrentThreadOwns();
+#else
     ::mozilla::detail::MutexImpl::unlock();
+#endif
   }
 
 #ifdef DEBUG