80 lines
2.9 KiB
C++
80 lines
2.9 KiB
C++
// Copyright 2013 The Chromium Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style license that can be
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// found in the LICENSE file.
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#ifndef MOJO_EDK_SYSTEM_WAITER_H_
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#define MOJO_EDK_SYSTEM_WAITER_H_
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#include <stdint.h>
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#include "base/logging.h"
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#include "base/macros.h"
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#include "base/synchronization/condition_variable.h"
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#include "base/synchronization/lock.h"
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#include "mojo/edk/system/awakable.h"
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#include "mojo/edk/system/system_impl_export.h"
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#include "mojo/public/c/system/types.h"
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namespace mojo {
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namespace edk {
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// IMPORTANT (all-caps gets your attention, right?): |Waiter| methods are called
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// under other locks, in particular, |Dispatcher::lock_|s, so |Waiter| methods
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// must never call out to other objects (in particular, |Dispatcher|s). This
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// class is thread-safe.
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class MOJO_SYSTEM_IMPL_EXPORT Waiter final : public Awakable {
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public:
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Waiter();
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~Waiter();
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// A |Waiter| can be used multiple times; |Init()| should be called before
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// each time it's used.
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void Init();
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// Waits until a suitable |Awake()| is called. (|context| may be null, in
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// which case, obviously no context is ever returned.)
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// Returns:
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// - The result given to the first call to |Awake()| (possibly before this
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// call to |Wait()|); in this case, |*context| is set to the value passed
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// to that call to |Awake()|.
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// - |MOJO_RESULT_DEADLINE_EXCEEDED| if the deadline was exceeded; in this
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// case |*context| is not modified.
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//
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// Usually, the context passed to |Awake()| will be the value passed to
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// |Dispatcher::AddAwakable()|, which is usually the index to the array of
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// handles passed to |MojoWaitMany()| (or 0 for |MojoWait()|).
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//
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// Typical |Awake()| results are:
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// - |MOJO_RESULT_OK| if one of the flags passed to
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// |MojoWait()|/|MojoWaitMany()| (hence |Dispatcher::AddAwakable()|) was
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// satisfied;
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// - |MOJO_RESULT_CANCELLED| if a handle (on which
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// |MojoWait()|/|MojoWaitMany()| was called) was closed (hence the
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// dispatcher closed); and
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// - |MOJO_RESULT_FAILED_PRECONDITION| if one of the set of flags passed to
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// |MojoWait()|/|MojoWaitMany()| cannot or can no longer be satisfied by
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// the corresponding handle (e.g., if the other end of a message or data
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// pipe is closed).
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MojoResult Wait(MojoDeadline deadline, uintptr_t* context);
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// Wake the waiter up with the given result and context (or no-op if it's been
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// woken up already).
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bool Awake(MojoResult result, uintptr_t context) override;
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private:
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base::Lock lock_; // Protects the following members.
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base::ConditionVariable cv_; // Associated to |lock_|.
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#if DCHECK_IS_ON()
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bool initialized_;
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#endif
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bool awoken_;
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MojoResult awake_result_;
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uintptr_t awake_context_;
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DISALLOW_COPY_AND_ASSIGN(Waiter);
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};
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} // namespace edk
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} // namespace mojo
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#endif // MOJO_EDK_SYSTEM_WAITER_H_
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