Pty reads a command's output and feeds it to Screen using an unbounded
queue.
However, if the command produces output faster than what `Screen` can
render, `Pty` still pushes it on the queue, causing it to grow
indefinitely, resulting in high memory usage and latency.
This patch fixes this by using a bounded queue between Pty and Screen,
so if Screen can't keep up with Pty, the queue will fill up, exerting
back pressure on Pty, making it read the command's output only as fast
as Screen renders it.
The unbounded queue is kept between Screen and producers other than Pty
to avoid a deadlock such as this scenario:
* pty thread filling up screen queue as soon as screen thread pops
something from it
* wasm thread is processing a Render instruction, blocking on the screen
queue
* screen thread is trying to render a plugin pane. It attempts to send a
Render insturction to the blocked wasm thread running the plugin.
This patch also adds a generous amount of sleeps to the integration
tests as having backpressure changes the timing of how instructions are
processed.
Fixes#525.
8ccf3d61a0