[ppapi] Simple deadlock detector for proxy lock.

ppapi/shared_impl/proxy_lock.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "ppapi/shared_impl/proxy_lock.h"
 
+#include "base/lazy_instance.h"
 #include "base/synchronization/lock.h"
+#include "base/threading/thread_local.h"
 #include "ppapi/shared_impl/ppapi_globals.h"
 
 namespace ppapi {
 
+// Simple single-thread deadlock detector for the proxy lock.
+// |true| when the current thread has the lock.
+base::LazyInstance<base::ThreadLocalBoolean>::Leaky
+    g_proxy_locked_on_thread = LAZY_INSTANCE_INITIALIZER;
+
 // static
 void ProxyLock::Acquire() {
   base::Lock* lock(PpapiGlobals::Get()->GetProxyLock());
-  if (lock)
+  if (lock) {
+    // This thread does not already hold the lock.
+    const bool deadlock = g_proxy_locked_on_thread.Get().Get();
+    CHECK(!deadlock);
+
     lock->Acquire();
+    g_proxy_locked_on_thread.Get().Set(true);
+  }
 }
 
 // static
 void ProxyLock::Release() {
   base::Lock* lock(PpapiGlobals::Get()->GetProxyLock());
-  if (lock)
+  if (lock) {
+    // This thread currently holds the lock.
+    const bool locked = g_proxy_locked_on_thread.Get().Get();
+    CHECK(locked);
+
+    g_proxy_locked_on_thread.Get().Set(false);
     lock->Release();
+  }
 }
 
 // static
 void ProxyLock::AssertAcquired() {
   base::Lock* lock(PpapiGlobals::Get()->GetProxyLock());
-  if (lock)
+  if (lock) {
+    // This thread currently holds the lock.
+    const bool locked = g_proxy_locked_on_thread.Get().Get();
+    CHECK(locked);
+
     lock->AssertAcquired();
+  }
 }
 
 void CallWhileUnlocked(const base::Closure& closure) {
   ProxyAutoUnlock lock;
   closure.Run();
 }
 
 void CallWhileLocked(const base::Closure& closure) {
   ProxyAutoLock lock;
   closure.Run();
 }
 
 }  // namespace ppapi