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* Copyright (C) 2012 The Android Open Source Project
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* See the License for the specific language governing permissions and
* limitations under the License.
#include <stdint.h>
#include <utils/Flattenable.h>
#include <utils/RefBase.h>
#include <utils/Timers.h>
namespace android {
class String8;
// ===========================================================================
// Fence
// ===========================================================================
class Fence
: public LightRefBase<Fence>, public Flattenable<Fence>
static const sp<Fence> NO_FENCE;
static constexpr nsecs_t SIGNAL_TIME_PENDING = INT64_MAX;
static constexpr nsecs_t SIGNAL_TIME_INVALID = -1;
static inline bool isValidTimestamp(nsecs_t time) {
return time >= 0 && time < INT64_MAX;
// TIMEOUT_NEVER may be passed to the wait method to indicate that it
// should wait indefinitely for the fence to signal.
enum { TIMEOUT_NEVER = -1 };
// Construct a new Fence object with an invalid file descriptor. This
// should be done when the Fence object will be set up by unflattening
// serialized data.
// Construct a new Fence object to manage a given fence file descriptor.
// When the new Fence object is destructed the file descriptor will be
// closed.
explicit Fence(int fenceFd);
// Not copyable or movable.
Fence(const Fence& rhs) = delete;
Fence& operator=(const Fence& rhs) = delete;
Fence(Fence&& rhs) = delete;
Fence& operator=(Fence&& rhs) = delete;
// Check whether the Fence has an open fence file descriptor. Most Fence
// methods treat an invalid file descriptor just like a valid fence that
// is already signalled, so using this is usually not necessary.
bool isValid() const { return mFenceFd != -1; }
// wait waits for up to timeout milliseconds for the fence to signal. If
// the fence signals then NO_ERROR is returned. If the timeout expires
// before the fence signals then -ETIME is returned. A timeout of
// TIMEOUT_NEVER may be used to indicate that the call should wait
// indefinitely for the fence to signal.
status_t wait(int timeout);
// waitForever is a convenience function for waiting forever for a fence to
// signal (just like wait(TIMEOUT_NEVER)), but issuing an error to the
// system log and fence state to the kernel log if the wait lasts longer
// than a warning timeout.
// The logname argument should be a string identifying
// the caller and will be included in the log message.
status_t waitForever(const char* logname);
// merge combines two Fence objects, creating a new Fence object that
// becomes signaled when both f1 and f2 are signaled (even if f1 or f2 is
// destroyed before it becomes signaled). The name argument specifies the
// human-readable name to associated with the new Fence object.
static sp<Fence> merge(const char* name, const sp<Fence>& f1,
const sp<Fence>& f2);
static sp<Fence> merge(const String8& name, const sp<Fence>& f1,
const sp<Fence>& f2);
// Return a duplicate of the fence file descriptor. The caller is
// responsible for closing the returned file descriptor. On error, -1 will
// be returned and errno will indicate the problem.
int dup() const;
// getSignalTime returns the system monotonic clock time at which the
// fence transitioned to the signaled state. If the fence is not signaled
// then SIGNAL_TIME_PENDING is returned. If the fence is invalid or if an
// error occurs then SIGNAL_TIME_INVALID is returned.
nsecs_t getSignalTime() const;
enum class Status {
Invalid, // Fence is invalid
Unsignaled, // Fence is valid but has not yet signaled
Signaled, // Fence is valid and has signaled
// getStatus() returns whether the fence has signaled yet. Prefer this to
// getSignalTime() or wait() if all you care about is whether the fence has
// signaled.
inline Status getStatus() {
// The sync_wait call underlying wait() has been measured to be
// significantly faster than the sync_fence_info call underlying
// getSignalTime(), which might otherwise appear to be the more obvious
// way to check whether a fence has signaled.
switch (wait(0)) {
case NO_ERROR:
return Status::Signaled;
case -ETIME:
return Status::Unsignaled;
return Status::Invalid;
// Flattenable interface
size_t getFlattenedSize() const;
size_t getFdCount() const;
status_t flatten(void*& buffer, size_t& size, int*& fds, size_t& count) const;
status_t unflatten(void const*& buffer, size_t& size, int const*& fds, size_t& count);
// Only allow instantiation using ref counting.
friend class LightRefBase<Fence>;
int mFenceFd;
}; // namespace android