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Diffstat (limited to 'security/sandbox/chromium/base/sequenced_task_runner.h')
| -rw-r--r-- | security/sandbox/chromium/base/sequenced_task_runner.h | 159 |
1 files changed, 159 insertions, 0 deletions
diff --git a/security/sandbox/chromium/base/sequenced_task_runner.h b/security/sandbox/chromium/base/sequenced_task_runner.h new file mode 100644 index 000000000..6bb3f2b87 --- /dev/null +++ b/security/sandbox/chromium/base/sequenced_task_runner.h @@ -0,0 +1,159 @@ +// 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. + +#ifndef BASE_SEQUENCED_TASK_RUNNER_H_ +#define BASE_SEQUENCED_TASK_RUNNER_H_ + +#include "base/base_export.h" +#include "base/sequenced_task_runner_helpers.h" +#include "base/task_runner.h" + +namespace base { + +// A SequencedTaskRunner is a subclass of TaskRunner that provides +// additional guarantees on the order that tasks are started, as well +// as guarantees on when tasks are in sequence, i.e. one task finishes +// before the other one starts. +// +// Summary +// ------- +// Non-nested tasks with the same delay will run one by one in FIFO +// order. +// +// Detailed guarantees +// ------------------- +// +// SequencedTaskRunner also adds additional methods for posting +// non-nestable tasks. In general, an implementation of TaskRunner +// may expose task-running methods which are themselves callable from +// within tasks. A non-nestable task is one that is guaranteed to not +// be run from within an already-running task. Conversely, a nestable +// task (the default) is a task that can be run from within an +// already-running task. +// +// The guarantees of SequencedTaskRunner are as follows: +// +// - Given two tasks T2 and T1, T2 will start after T1 starts if: +// +// * T2 is posted after T1; and +// * T2 has equal or higher delay than T1; and +// * T2 is non-nestable or T1 is nestable. +// +// - If T2 will start after T1 starts by the above guarantee, then +// T2 will start after T1 finishes and is destroyed if: +// +// * T2 is non-nestable, or +// * T1 doesn't call any task-running methods. +// +// - If T2 will start after T1 finishes by the above guarantee, then +// all memory changes in T1 and T1's destruction will be visible +// to T2. +// +// - If T2 runs nested within T1 via a call to the task-running +// method M, then all memory changes in T1 up to the call to M +// will be visible to T2, and all memory changes in T2 will be +// visible to T1 from the return from M. +// +// Note that SequencedTaskRunner does not guarantee that tasks are run +// on a single dedicated thread, although the above guarantees provide +// most (but not all) of the same guarantees. If you do need to +// guarantee that tasks are run on a single dedicated thread, see +// SingleThreadTaskRunner (in single_thread_task_runner.h). +// +// Some corollaries to the above guarantees, assuming the tasks in +// question don't call any task-running methods: +// +// - Tasks posted via PostTask are run in FIFO order. +// +// - Tasks posted via PostNonNestableTask are run in FIFO order. +// +// - Tasks posted with the same delay and the same nestable state +// are run in FIFO order. +// +// - A list of tasks with the same nestable state posted in order of +// non-decreasing delay is run in FIFO order. +// +// - A list of tasks posted in order of non-decreasing delay with at +// most a single change in nestable state from nestable to +// non-nestable is run in FIFO order. (This is equivalent to the +// statement of the first guarantee above.) +// +// Some theoretical implementations of SequencedTaskRunner: +// +// - A SequencedTaskRunner that wraps a regular TaskRunner but makes +// sure that only one task at a time is posted to the TaskRunner, +// with appropriate memory barriers in between tasks. +// +// - A SequencedTaskRunner that, for each task, spawns a joinable +// thread to run that task and immediately quit, and then +// immediately joins that thread. +// +// - A SequencedTaskRunner that stores the list of posted tasks and +// has a method Run() that runs each runnable task in FIFO order +// that can be called from any thread, but only if another +// (non-nested) Run() call isn't already happening. +class BASE_EXPORT SequencedTaskRunner : public TaskRunner { + public: + // The two PostNonNestable*Task methods below are like their + // nestable equivalents in TaskRunner, but they guarantee that the + // posted task will not run nested within an already-running task. + // + // A simple corollary is that posting a task as non-nestable can + // only delay when the task gets run. That is, posting a task as + // non-nestable may not affect when the task gets run, or it could + // make it run later than it normally would, but it won't make it + // run earlier than it normally would. + + // TODO(akalin): Get rid of the boolean return value for the methods + // below. + + bool PostNonNestableTask(const tracked_objects::Location& from_here, + const Closure& task); + + virtual bool PostNonNestableDelayedTask( + const tracked_objects::Location& from_here, + const Closure& task, + base::TimeDelta delay) = 0; + + // Submits a non-nestable task to delete the given object. Returns + // true if the object may be deleted at some point in the future, + // and false if the object definitely will not be deleted. + template <class T> + bool DeleteSoon(const tracked_objects::Location& from_here, + const T* object) { + return + subtle::DeleteHelperInternal<T, bool>::DeleteViaSequencedTaskRunner( + this, from_here, object); + } + + // Submits a non-nestable task to release the given object. Returns + // true if the object may be released at some point in the future, + // and false if the object definitely will not be released. + template <class T> + bool ReleaseSoon(const tracked_objects::Location& from_here, + T* object) { + return + subtle::ReleaseHelperInternal<T, bool>::ReleaseViaSequencedTaskRunner( + this, from_here, object); + } + + protected: + ~SequencedTaskRunner() override {} + + private: + template <class T, class R> friend class subtle::DeleteHelperInternal; + template <class T, class R> friend class subtle::ReleaseHelperInternal; + + bool DeleteSoonInternal(const tracked_objects::Location& from_here, + void(*deleter)(const void*), + const void* object); + + bool ReleaseSoonInternal(const tracked_objects::Location& from_here, + void(*releaser)(const void*), + const void* object); +}; + +} // namespace base + +#endif // BASE_SEQUENCED_TASK_RUNNER_H_ |