Adding upstream version 124.0.1.upstream/124.0.1

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 116 insertions, 0 deletions

diff --git a/ipc/chromium/src/base/condition_variable.h b/ipc/chromium/src/base/condition_variable.h
new file mode 100644
index 0000000000..0b82824ce6
--- /dev/null
+++ b/ipc/chromium/src/base/condition_variable.h
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+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+// 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 managed thread pool.
+// 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_CONDITION_VARIABLE_H_
+#define BASE_CONDITION_VARIABLE_H_
+
+#include "base/basictypes.h"
+#include "base/lock.h"
+
+#if defined(XP_UNIX)
+#  include <pthread.h>
+#endif
+
+#if defined(XP_WIN)
+#  include <windows.h>
+#endif
+
+namespace base {
+class TimeDelta;
+}
+
+class 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. The wait functions are
+  // susceptible to spurious wakeups. (See usage note 1 for more details.)
+  void Wait();
+  void TimedWait(const base::TimeDelta& max_time);
+
+  // Broadcast() revives all waiting threads. (See usage note 2 for more
+  // details.)
+  void Broadcast();
+  // Signal() revives one waiting thread.
+  void Signal();
+
+ private:
+#if defined(XP_WIN)
+  CONDITION_VARIABLE cv_;
+  SRWLOCK* const srwlock_;
+#else
+  pthread_cond_t condition_;
+  pthread_mutex_t* user_mutex_;
+#endif
+
+  DISALLOW_COPY_AND_ASSIGN(ConditionVariable);
+};
+
+#endif  // BASE_CONDITION_VARIABLE_H_