1 files changed, 85 insertions, 0 deletions
diff --git a/js/src/threading/Mutex.cpp b/js/src/threading/Mutex.cpp
new file mode 100644
index 0000000000..8a57db4755
--- /dev/null
+++ b/js/src/threading/Mutex.cpp
@@ -0,0 +1,85 @@
+/* -*- 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 "threading/Mutex.h"
+
+using namespace js;
+
+#ifdef DEBUG
+
+MOZ_THREAD_LOCAL(js::Mutex*) js::Mutex::HeldMutexStack;
+
+/* static */
+bool js::Mutex::Init() { return HeldMutexStack.init(); }
+
+void js::Mutex::lock() {
+  preLockChecks();
+  impl_.lock();
+  postLockChecks();
+}
+
+bool js::Mutex::tryLock() {
+  preLockChecks();
+  if (!impl_.tryLock()) {
+    return false;
+  }
+
+  postLockChecks();
+  return true;
+}
+
+void js::Mutex::preLockChecks() const {
+  Mutex* prev = HeldMutexStack.get();
+  if (prev) {
+    if (id_.order <= prev->id_.order) {
+      fprintf(stderr,
+              "Attempt to acquire mutex %s with order %u while holding %s with "
+              "order %u\n",
+              id_.name, id_.order, prev->id_.name, prev->id_.order);
+      MOZ_CRASH("Mutex ordering violation");
+    }
+  }
+}
+
+void js::Mutex::postLockChecks() {
+  MOZ_ASSERT(!owningThread_);
+  owningThread_ = ThreadId::ThisThreadId();
+
+  MOZ_ASSERT(prev_ == nullptr);
+  prev_ = HeldMutexStack.get();
+  HeldMutexStack.set(this);
+}
+
+void js::Mutex::unlock() {
+  preUnlockChecks();
+  impl_.unlock();
+}
+
+void js::Mutex::preUnlockChecks() {
+  Mutex* stack = HeldMutexStack.get();
+  MOZ_ASSERT(stack == this);
+  HeldMutexStack.set(prev_);
+  prev_ = nullptr;
+
+  MOZ_ASSERT(ThreadId::ThisThreadId() == owningThread_);
+  owningThread_ = ThreadId();
+}
+
+void js::Mutex::assertOwnedByCurrentThread() const {
+  // This check is only thread-safe if it succeeds.
+  MOZ_ASSERT(ThreadId::ThisThreadId() == owningThread_);
+
+  // Check the mutex is on the mutex stack.
+  for (Mutex* mutex = HeldMutexStack.get(); mutex; mutex = mutex->prev_) {
+    if (mutex == this) {
+      return;
+    }
+  }
+
+  MOZ_CRASH("Mutex not found on the stack of held mutexes");
+}
+
+#endif