chromium/third_party/dawn/src/dawn/native/SystemEvent.h

// Copyright 2023 The Dawn & Tint Authors
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#ifndef SRC_DAWN_NATIVE_SYSTEMEVENT_H_
#define SRC_DAWN_NATIVE_SYSTEMEVENT_H_

#include <optional>
#include <utility>

#include "dawn/common/MutexProtected.h"
#include "dawn/common/NonCopyable.h"
#include "dawn/common/Platform.h"
#include "dawn/common/RefCounted.h"
#include "dawn/native/IntegerTypes.h"
#include "dawn/native/SystemHandle.h"

namespace dawn::native {

class SystemEventPipeSender;

// SystemEventReceiver holds an OS event primitive (Win32 Event Object or POSIX file descriptor (fd)
// that will be signalled by some other thing: either an OS integration like SetEventOnCompletion(),
// or our own code like SystemEventPipeSender.
//
// SystemEventReceiver is one-time-use (to make it easier to use correctly) - once it's been
// signalled, it won't ever get reset (become unsignalled). Instead, if we want to reuse underlying
// OS objects, it should be reset and recycled *after* the SystemEventReceiver and
// SystemEventPipeSender have been destroyed.
class SystemEventReceiver final : NonCopyable { … };

// See CreateSystemEventPipe.
class SystemEventPipeSender final : NonCopyable { … };

// CreateSystemEventPipe provides an SystemEventReceiver that can be signalled by Dawn code. This is
// useful for queue completions on Metal (where Metal signals us by calling a callback) and for
// async pipeline creations that happen in a worker-thread task.
//
// We use OS events even for these because, unlike C++/pthreads primitives (mutexes, atomics,
// condvars, etc.), it's possible to wait-any on them (wait for any of a list of events to fire).
// Other use-cases in Dawn that don't require wait-any should generally use C++ primitives, for
// example for signalling the completion of other types of worker-thread work that don't need to
// signal a WGPUFuture.
//
// SystemEventReceiver is one-time-use (see its docs), so there's no way to reset an
// SystemEventPipeSender.
//
// - On Windows, SystemEventReceiver is a Win32 Event Object, so we can create one with
//   CreateEvent() and signal it with SetEvent().
// - On POSIX, SystemEventReceiver is a file descriptor (fd), so we can create one with pipe(), and
//   signal it by write()ing into the pipe (to make it become readable, though we won't read() it).
std::pair<SystemEventPipeSender, SystemEventReceiver> CreateSystemEventPipe();

class SystemEvent : public RefCounted { … };

}  // namespace dawn::native

#endif  // SRC_DAWN_NATIVE_SYSTEMEVENT_H_