Add base to the repository.

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@8 0039d316-1c4b-4281-b951-d872f2087c98

1 files changed, 156 insertions, 0 deletions

diff --git a/base/lock.cc b/base/lock.cc
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+// Copyright 2008, Google Inc.
+// All rights reserved.
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//    * Redistributions of source code must retain the above copyright
+// notice, this list of conditions and the following disclaimer.
+//    * Redistributions in binary form must reproduce the above
+// copyright notice, this list of conditions and the following disclaimer
+// in the documentation and/or other materials provided with the
+// distribution.
+//    * Neither the name of Google Inc. nor the names of its
+// contributors may be used to endorse or promote products derived from
+// this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+// 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.
+
+#include "base/lock.h"
+#include "base/logging.h"
+
+Lock::Lock()
+    : lock_()
+    , recursion_count_shadow_(0) {
+#ifndef NDEBUG
+  recursion_used_ = false;
+  acquisition_count_ = 0;
+  contention_count_ = 0;
+#endif
+}
+
+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.
+    recursion_used_ = true;
+#endif  // NDEBUG
+}
+
+void Lock::Release() {
+  --recursion_count_shadow_;  // ONLY access while lock is still held.
+#ifndef NDEBUG
+  DCHECK(0 <= recursion_count_shadow_);
+#endif
+  lock_.Unlock();
+}
+
+bool Lock::Try() {
+  if (lock_.Try()) {
+    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.
+      recursion_used_ = true;
+#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();
+}