Disallow Lock class support for recursive locking

base/lock.cc

 // Copyright (c) 2006-2008 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.
 
 // Provide place to put profiling methods for the
 // Lock class.
 // The Lock class is used everywhere, and hence any changes
 // to lock.h tend to require a complete rebuild.  To facilitate
 // profiler development, all the profiling methods are listed
-// here.  Note that they are only instantiated in a debug
-// build, and the header provides all the trivial implementations
-// in a production build.
+// here.  
 
 #include "base/lock.h"
 #include "base/logging.h"
 
+#ifndef NDEBUG
 Lock::Lock()
     : lock_(),
-      recursion_count_shadow_(0) {
-#ifndef NDEBUG
-  recursion_used_ = false;
-  acquisition_count_ = 0;
-  contention_count_ = 0;
-#endif
+      recursion_count_shadow_(0),
+      recursion_used_(false),
+      acquisition_count_(0),
+      contention_count_(0) {
 }
+#else  // NDEBUG
+Lock::Lock()
+    : lock_() {
+}
+#endif  // NDEBUG
 
 Lock::~Lock() {
-#ifndef NDEBUG
-  // There should be no one to contend for the lock,
-  // ...but we need the memory barrier to get a good value.
-  lock_.Lock();
-  int final_recursion_count = recursion_count_shadow_;
-  lock_.Unlock();
-#endif
-
-  // Allow unit test exception only at end of method.
-#ifndef NDEBUG
-  DCHECK(0 == final_recursion_count);
-#endif
 }
 
 void Lock::Acquire() {
 #ifdef NDEBUG
   lock_.Lock();
-  recursion_count_shadow_++;
 #else  // NDEBUG
   if (!lock_.Try()) {
     // We have contention.
     lock_.Lock();
     contention_count_++;
   }
   // ONLY access data after locking.
   recursion_count_shadow_++;
-  if (1 == recursion_count_shadow_)
-    acquisition_count_++;
-  else if (2 == recursion_count_shadow_ && !recursion_used_)
-    // Usage Note: Set a break point to debug.
+  acquisition_count_++;
+  if (2 == recursion_count_shadow_ && !recursion_used_) {
     recursion_used_ = true;
+    // TODO(sky): Uncomment this DCHECK after fixing test cases.
+    // DCHECK(false);  // Catch accidental redundant lock acquisition.
+  }
 #endif  // NDEBUG
 }
 
 void Lock::Release() {
+#ifndef NDEBUG
   --recursion_count_shadow_;  // ONLY access while lock is still held.
-#ifndef NDEBUG
   DCHECK(0 <= recursion_count_shadow_);
-#endif
+#endif  // NDEBUG
   lock_.Unlock();
 }
 
 bool Lock::Try() {
   if (lock_.Try()) {
+#ifndef NDEBUG
     recursion_count_shadow_++;
-#ifndef NDEBUG
-    if (1 == recursion_count_shadow_)
-      acquisition_count_++;
-    else if (2 == recursion_count_shadow_ && !recursion_used_)
-      // Usage Note: Set a break point to debug.
+    acquisition_count_++;
+    if (2 == recursion_count_shadow_ && !recursion_used_) {
       recursion_used_ = true;
+      DCHECK(false);  // Catch accidental redundant lock acquisition.
+    }
 #endif
     return true;
   } else {
     return false;
   }
 }
-
-// GetCurrentThreadRecursionCount returns the number of nested Acquire() calls
-// that have been made by the current thread holding this lock.  The calling
-// thread is ***REQUIRED*** to be *currently* holding the lock.   If that
-// calling requirement is violated, the return value is not well defined.
-// Return results are guaranteed correct if the caller has acquired this lock.
-// The return results might be incorrect otherwise.
-// This method is designed to be fast in non-debug mode by co-opting
-// synchronization using lock_ (no additional synchronization is used), but in
-// debug mode it slowly and carefully validates the requirement (and fires a
-// a DCHECK if it was called incorrectly).
-int32 Lock::GetCurrentThreadRecursionCount() {
-#ifndef NDEBUG
-  // If this DCHECK fails, then the most probable cause is:
-  // This method was called by class AutoUnlock during processing of a
-  // Wait() call made into the ConditonVariable class. That call to
-  // Wait() was made (incorrectly) without first Aquiring this Lock
-  // instance.
-  lock_.Lock();
-  int temp = recursion_count_shadow_;
-  lock_.Unlock();
-  // Unit tests catch an exception, so we need to be careful to test
-  // outside the critical section, since the Leave would be skipped!?!
-  DCHECK(temp >= 1);  // Allow unit test exception only at end of method.
-#endif  // DEBUG
-
-  // We hold lock, so this *is* correct value.
-  return recursion_count_shadow_;
-}
-
-
-AutoUnlock::AutoUnlock(Lock& lock) : lock_(&lock), release_count_(0) {
-  // We require our caller have the lock, so we can call for recursion count.
-  // CRITICALLY: Fetch value before we release the lock.
-  int32 count = lock_->GetCurrentThreadRecursionCount();
-  DCHECK(count > 0);  // Make sure we owned the lock.
-  while (count-- > 0) {
-    release_count_++;
-    lock_->Release();
-  }
-}
-
-AutoUnlock::~AutoUnlock() {
-  DCHECK(release_count_ >= 0);
-  while (release_count_-- > 0)
-    lock_->Acquire();
-}
-