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// Copyright 2016 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 MOJO_EDK_SYSTEM_REQUEST_CONTEXT_H_
#define MOJO_EDK_SYSTEM_REQUEST_CONTEXT_H_
#include "base/containers/stack_container.h"
#include "base/macros.h"
#include "mojo/edk/system/handle_signals_state.h"
#include "mojo/edk/system/system_impl_export.h"
#include "mojo/edk/system/watcher.h"
namespace base {
template<typename T> class ThreadLocalPointer;
}
namespace mojo {
namespace edk {
// A RequestContext is a thread-local object which exists for the duration of
// a single system API call. It is constructed immediately upon EDK entry and
// destructed immediately before returning to the caller, after any internal
// locks have been released.
//
// NOTE: It is legal to construct a RequestContext while another one already
// exists on the current thread, but it is not safe to use the nested context
// for any reason. Therefore it is important to always use
// |RequestContext::current()| rather than referring to any local instance
// directly.
class MOJO_SYSTEM_IMPL_EXPORT RequestContext {
public:
// Identifies the source of the current stack frame's RequestContext.
enum class Source {
LOCAL_API_CALL,
SYSTEM,
};
// Constructs a RequestContext with a LOCAL_API_CALL Source.
RequestContext();
explicit RequestContext(Source source);
~RequestContext();
// Returns the current thread-local RequestContext.
static RequestContext* current();
Source source() const { return source_; }
// Adds a finalizer to this RequestContext corresponding to a watch callback
// which should be triggered in response to some handle state change. If
// the Watcher hasn't been cancelled by the time this RequestContext is
// destroyed, its WatchCallback will be invoked with |result| and |state|
// arguments.
void AddWatchNotifyFinalizer(scoped_refptr<Watcher> watcher,
MojoResult result,
const HandleSignalsState& state);
// Adds a finalizer to this RequestContext which cancels a watch.
void AddWatchCancelFinalizer(scoped_refptr<Watcher> watcher);
private:
// Is this request context the current one?
bool IsCurrent() const;
struct WatchNotifyFinalizer {
WatchNotifyFinalizer(scoped_refptr<Watcher> watcher,
MojoResult result,
const HandleSignalsState& state);
WatchNotifyFinalizer(const WatchNotifyFinalizer& other);
~WatchNotifyFinalizer();
scoped_refptr<Watcher> watcher;
MojoResult result;
HandleSignalsState state;
};
// Chosen by fair dice roll.
//
// TODO: We should measure the distribution of # of finalizers typical to
// any RequestContext and adjust this number accordingly. It's probably
// almost always 1, but 4 seems like a harmless upper bound for now.
static const size_t kStaticWatchFinalizersCapacity = 4;
using WatchNotifyFinalizerList =
base::StackVector<WatchNotifyFinalizer, kStaticWatchFinalizersCapacity>;
using WatchCancelFinalizerList =
base::StackVector<scoped_refptr<Watcher>, kStaticWatchFinalizersCapacity>;
const Source source_;
WatchNotifyFinalizerList watch_notify_finalizers_;
WatchCancelFinalizerList watch_cancel_finalizers_;
// Pointer to the TLS context. Although this can easily be accessed via the
// global LazyInstance, accessing a LazyInstance has a large cost relative to
// the rest of this class and its usages.
base::ThreadLocalPointer<RequestContext>* tls_context_;
DISALLOW_COPY_AND_ASSIGN(RequestContext);
};
} // namespace edk
} // namespace mojo
#endif // MOJO_EDK_SYSTEM_REQUEST_CONTEXT_H_