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Diffstat (limited to 'security/sandbox/chromium/base/synchronization/condition_variable.h')
| -rw-r--r-- | security/sandbox/chromium/base/synchronization/condition_variable.h | 118 |
1 files changed, 0 insertions, 118 deletions
diff --git a/security/sandbox/chromium/base/synchronization/condition_variable.h b/security/sandbox/chromium/base/synchronization/condition_variable.h deleted file mode 100644 index a41b2ba5a..000000000 --- a/security/sandbox/chromium/base/synchronization/condition_variable.h +++ /dev/null @@ -1,118 +0,0 @@ -// Copyright (c) 2011 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. - -// ConditionVariable wraps pthreads condition variable synchronization or, on -// Windows, simulates it. This functionality is very helpful for having -// several threads wait for an event, as is common with a thread pool managed -// by a master. The meaning of such an event in the (worker) thread pool -// scenario is that additional tasks are now available for processing. It is -// used in Chrome in the DNS prefetching system to notify worker threads that -// a queue now has items (tasks) which need to be tended to. A related use -// would have a pool manager waiting on a ConditionVariable, waiting for a -// thread in the pool to announce (signal) that there is now more room in a -// (bounded size) communications queue for the manager to deposit tasks, or, -// as a second example, that the queue of tasks is completely empty and all -// workers are waiting. -// -// USAGE NOTE 1: spurious signal events are possible with this and -// most implementations of condition variables. As a result, be -// *sure* to retest your condition before proceeding. The following -// is a good example of doing this correctly: -// -// while (!work_to_be_done()) Wait(...); -// -// In contrast do NOT do the following: -// -// if (!work_to_be_done()) Wait(...); // Don't do this. -// -// Especially avoid the above if you are relying on some other thread only -// issuing a signal up *if* there is work-to-do. There can/will -// be spurious signals. Recheck state on waiting thread before -// assuming the signal was intentional. Caveat caller ;-). -// -// USAGE NOTE 2: Broadcast() frees up all waiting threads at once, -// which leads to contention for the locks they all held when they -// called Wait(). This results in POOR performance. A much better -// approach to getting a lot of threads out of Wait() is to have each -// thread (upon exiting Wait()) call Signal() to free up another -// Wait'ing thread. Look at condition_variable_unittest.cc for -// both examples. -// -// Broadcast() can be used nicely during teardown, as it gets the job -// done, and leaves no sleeping threads... and performance is less -// critical at that point. -// -// The semantics of Broadcast() are carefully crafted so that *all* -// threads that were waiting when the request was made will indeed -// get signaled. Some implementations mess up, and don't signal them -// all, while others allow the wait to be effectively turned off (for -// a while while waiting threads come around). This implementation -// appears correct, as it will not "lose" any signals, and will guarantee -// that all threads get signaled by Broadcast(). -// -// This implementation offers support for "performance" in its selection of -// which thread to revive. Performance, in direct contrast with "fairness," -// assures that the thread that most recently began to Wait() is selected by -// Signal to revive. Fairness would (if publicly supported) assure that the -// thread that has Wait()ed the longest is selected. The default policy -// may improve performance, as the selected thread may have a greater chance of -// having some of its stack data in various CPU caches. -// -// For a discussion of the many very subtle implementation details, see the FAQ -// at the end of condition_variable_win.cc. - -#ifndef BASE_SYNCHRONIZATION_CONDITION_VARIABLE_H_ -#define BASE_SYNCHRONIZATION_CONDITION_VARIABLE_H_ - -#include "base/base_export.h" -#include "base/logging.h" -#include "base/macros.h" -#include "base/synchronization/lock.h" -#include "build/build_config.h" - -#if defined(OS_POSIX) -#include <pthread.h> -#endif - -namespace base { - -class ConditionVarImpl; -class TimeDelta; - -class BASE_EXPORT ConditionVariable { - public: - // Construct a cv for use with ONLY one user lock. - explicit ConditionVariable(Lock* user_lock); - - ~ConditionVariable(); - - // Wait() releases the caller's critical section atomically as it starts to - // sleep, and the reacquires it when it is signaled. - void Wait(); - void TimedWait(const TimeDelta& max_time); - - // Broadcast() revives all waiting threads. - void Broadcast(); - // Signal() revives one waiting thread. - void Signal(); - - private: - -#if defined(OS_WIN) - ConditionVarImpl* impl_; -#elif defined(OS_POSIX) - pthread_cond_t condition_; - pthread_mutex_t* user_mutex_; -#if DCHECK_IS_ON() - base::Lock* user_lock_; // Needed to adjust shadow lock state on wait. -#endif - -#endif - - DISALLOW_COPY_AND_ASSIGN(ConditionVariable); -}; - -} // namespace base - -#endif // BASE_SYNCHRONIZATION_CONDITION_VARIABLE_H_ |