class ClientVsyncQueue

Defined at line 37 of file ../../src/graphics/display/drivers/coordinator/client-vsync-queue.h

Traffic shaper for VSync messages sent to a Coordinator client.

Under normal operation, VSync messages are generated at a high frequency.

Clients designed for throughput rather than latency may occasionally take a

long time to process a VSync. Without traffic shaping, this would result in a

long queue of unprocessed FIDL messages, creating memory pressure.

This traffic shaper avoids the situation described above. Clients are

occasionally asked to acknowledge VSync messages, to provide a backpressure

signal. When a client falls behind, a fixed number of VSync messages are

buffered. If the buffer fills up, older messages are discarded in favor of

newer messages.

Instances are not thread-safe. Concurrent access must be synchronized

externally.

Public Members

static const int32_t kThrottleWatermark

static const int32_t kRequestAckWatermark

static const int32_t kThrottleBufferSize

void ClientVsyncQueue ()

Creates a queue that does not deliver received VSync events.

Defined at line 15 of file ../../src/graphics/display/drivers/coordinator/client-vsync-queue.cc

void ClientVsyncQueue (uint64_t cookie_salt)

Provided to make tests deterministic.

Defined at line 13 of file ../../src/graphics/display/drivers/coordinator/client-vsync-queue.cc

void ~ClientVsyncQueue ()

Defined at line 17 of file ../../src/graphics/display/drivers/coordinator/client-vsync-queue.cc

void Push (const Message & message)

Registers a VSync message to be sent to the Coordinator client.

If the queue is full, the oldest VSync message will be overwritten.

`DrainUntilThrottled()` must be called before any other method is called.

Defined at line 19 of file ../../src/graphics/display/drivers/coordinator/client-vsync-queue.cc

bool Acknowledge (display::VsyncAckCookie ack_cookie)

Called when a client acknowledges a VSync.

`ack_cookie` must not be invalid.

Returns false if `ack_cookie` is not a correct acknowledgement cookie.

If this method succeeds, `DrainUntilThrottled()` must be called before any

other method is called.

Defined at line 29 of file ../../src/graphics/display/drivers/coordinator/client-vsync-queue.cc

void ClientVsyncQueue (const ClientVsyncQueue & )

Defined at line 63 of file ../../src/graphics/display/drivers/coordinator/client-vsync-queue.h

ClientVsyncQueue & operator= (const ClientVsyncQueue & )

Defined at line 64 of file ../../src/graphics/display/drivers/coordinator/client-vsync-queue.h

template <typename Callable>

void DrainUntilThrottled (Callable send_message)

Removes all the messages eligible to be sent to the Coordinator client.

`send_message` must take two arguments, a `const

ClientVsyncQueue::Message

` and a `display::VsyncAckCookie`, and must

attempt to send the VSync message described by the arguments.

`send_message` must not make any method calls on this queue.

`send_message` receives messages in the same order that they were given to

`Push()`.

Defined at line 131 of file ../../src/graphics/display/drivers/coordinator/client-vsync-queue.h