SyncFence
class SyncFence : AutoCloseable, Parcelable
| kotlin.Any | |
| ↳ | android.hardware.SyncFence |
A SyncFence represents a synchronization primitive which signals when hardware units have completed work on a particular resource. They initially start in an unsignaled state and make a one-time transition to either a signaled or error state. SyncFences are created by various device APIs in response to submitting tasks to the device. They cannot be created nor signaled by userspace. As a result, this means that a SyncFence will make always make forward progress.
SyncFence's generally come in one of two varieties. "Presentation fences" refer to a SyncFence when the writing to a buffer has finished. "Release fences" then refer to when the reading from a buffer has finished.
For example, a GPU rendering to a framebuffer may generate a synchronization fence, e.g., an EGLSync or VkFence, which signals when rendering has completed. Once the fence signals, then the backing storage for the framebuffer may be safely read from, such as for display or for media encoding. This would be referred to as a "presentation fence."
Similarly when using an android.media.ImageWriter it is possible that an android.media.Image returned by ImageWriter.dequeueInputImage() may already have a fence set on it. This would be what is referred to as either a "release fence" or an "acqurie fence" and indicates the fence that the writer must wait on before writing to the underlying buffer. In the case of ImageWriter this is done automatically when eg Image.getPlanes() is called, however when using Image.getHardwareBuffer() it is the caller's responsibility to ensure the release fence has signaled before writing to the buffer.
Summary
| Constants | |
|---|---|
| static Long |
An invalid signal time. |
| static Long |
A pending signal time. |
| Inherited constants | |
|---|---|
| Public constructors | |
|---|---|
|
Creates a copy of the SyncFence from an existing one. |
|
| Public methods | |
|---|---|
| Boolean |
Waits for a SyncFence to signal for up to the timeout duration. |
| Boolean |
Waits forever for a SyncFence to signal. |
| Unit |
close()Close the SyncFence. |
| Int | |
| Long |
Returns the time in nanoseconds that the fence signaled in the CLOCK_MONOTONIC time domain. |
| Boolean |
isValid()Checks if the SyncFile object is valid. |
| Unit |
writeToParcel(out: Parcel, flags: Int)Flatten this object into a Parcel. |
| Properties | |
|---|---|
| static Parcelable.Creator<SyncFence!> | |
Constants
SIGNAL_TIME_INVALID
static val SIGNAL_TIME_INVALID: Long
An invalid signal time. Represents either the signal time for a SyncFence that isn't valid (that is, isValid() is false), or if an error occurred while attempting to retrieve the signal time.
Value: -1LSIGNAL_TIME_PENDING
static val SIGNAL_TIME_PENDING: Long
A pending signal time. This is equivalent to the max value of a long, representing an infinitely far point in the future.
Value: 9223372036854775807LPublic constructors
SyncFence
SyncFence(other: SyncFence)
Creates a copy of the SyncFence from an existing one. Both fences must be closed() independently.
| Parameters | |
|---|---|
other |
SyncFence: This value cannot be null. |
Public methods
await
fun await(timeout: Duration): Boolean
Waits for a SyncFence to signal for up to the timeout duration. An invalid SyncFence, that is if isValid() is false, is treated equivalently to a SyncFence that has already signaled. That is, wait() will immediately return true.
| Parameters | |
|---|---|
timeout |
Duration: The timeout duration. If the duration is negative, then this waits forever. This value cannot be null. |
| Return | |
|---|---|
Boolean |
true if the fence signaled or isn't valid, false otherwise. |
awaitForever
fun awaitForever(): Boolean
Waits forever for a SyncFence to signal. An invalid SyncFence, that is if isValid() is false, is treated equivalently to a SyncFence that has already signaled. That is, wait() will immediately return true.
| Return | |
|---|---|
Boolean |
true if the fence signaled or isn't valid, false otherwise. |
close
fun close(): Unit
Close the SyncFence. This implementation closes the underlying OS resources allocated this stream.
| Exceptions | |
|---|---|
java.lang.Exception |
if this resource cannot be closed |
describeContents
fun describeContents(): Int
| Return | |
|---|---|
Int |
a bitmask indicating the set of special object types marshaled by this Parcelable object instance. Value is either 0 or android.os.Parcelable#CONTENTS_FILE_DESCRIPTOR |
getSignalTime
fun getSignalTime(): Long
Returns the time in nanoseconds that the fence signaled in the CLOCK_MONOTONIC time domain. This corresponds to System.nanoTime() but may also be compared to SystemClock.uptimeMillis() after adjusting for milliseconds vs. nanoseconds. If the fence isn't valid, that is if isValid() is false, then this returns SIGNAL_TIME_INVALID. Similarly, if an error occurs while trying to access the signal time, then SIGNAL_TIME_INVALID is also returned. If the fence hasn't yet signaled, then SIGNAL_TIME_PENDING is returned.
| Return | |
|---|---|
Long |
The time the fence signaled, SIGNAL_TIME_INVALID if there's an error, or SIGNAL_TIME_PENDING if the fence hasn't signaled yet. |
isValid
fun isValid(): Boolean
Checks if the SyncFile object is valid.
| Return | |
|---|---|
Boolean |
true if the file descriptor represents a valid, open file; false otherwise. |
writeToParcel
fun writeToParcel(
out: Parcel,
flags: Int
): Unit
Flatten this object into a Parcel.
| Parameters | |
|---|---|
dest |
The Parcel in which the object should be written. This value cannot be null. |
flags |
Int: Additional flags about how the object should be written. May be 0 or PARCELABLE_WRITE_RETURN_VALUE |
out |
Parcel: The Parcel in which the object should be written. This value cannot be null. |