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