# Waiting and retrying

Source: https://libtmux.org/en/csharp/latest/topics/waiting-and-retry/

> Polling a condition instead of guessing a sleep, and tmux's own wait-for signal channel as the alternative to polling.

After sending input or starting a process, wait for the state your next step
requires. [Pane
interaction](https://libtmux.org/en/csharp/latest/topics/pane-interaction/#waiting-for-something-to-finish) covers
waiting for screen text. This page covers arbitrary conditions and tmux's named
`wait-for` signal channels.

## Polling a condition

Polling checks a condition repeatedly until it succeeds or a deadline expires.
Set a deadline and choose an interval that limits unnecessary tmux commands.

**Helper:** [`LibTmux.Testing.TmuxWait.UntilAsync(probe, timeout, interval)`](<https://libtmux.org/en/csharp/latest/reference/libtmux-tmuxwait-untilasync/>)

**Where it lives:** the separate [`LibTmux.Testing`](<https://libtmux.org/en/csharp/latest/reference/#LibTmux.Testing>) package

### Examples

```csharp
await LibTmux.Testing.TmuxWait.UntilAsync(
    async ct => (await session.GetWindowsAsync(ct)).Any(w => w.Name == "build"),
    TimeSpan.FromSeconds(5),
    TimeSpan.FromMilliseconds(50));
```

## tmux's own wait-for channel

Use `tmux wait-for -S <channel>` to signal and `tmux wait-for <channel>` to
block until signalled. This avoids repeated screen captures when the command can
announce its own completion:

[`Server.OpenWaitChannel`](<https://libtmux.org/en/csharp/latest/reference/libtmux-server-openwaitchannel/>) returns a [`TmuxWaitChannel`](<https://libtmux.org/en/csharp/latest/reference/libtmux-tmuxwaitchannel/>). Keep it in
an `await using` scope and call [`WaitAsync`](<https://libtmux.org/en/csharp/latest/reference/libtmux-tmuxwaitchannel-waitasync/>) with a budget. Select the
signal mode to signal the channel.

```csharp
await using TmuxWaitChannel channel = server.OpenWaitChannel("built");
bool signalled = await channel.WaitAsync(TimeSpan.FromSeconds(5));
```

tmux remembers a signal sent before a waiter starts. The next wait on that
channel returns immediately, so completion is not lost when the command finishes
first.

A raw `wait-for` client can exit zero when the server dies, as well as when the
channel is signalled. Verify server liveness when a lost server must be treated
as a failed task.

Use a channel name specific to the task. A remembered signal can otherwise
satisfy an unrelated later wait.

<details>
<summary>tmux manual and source</summary>

The tmux manual describes [completion channels](https://github.com/tmux/tmux/blob/94796f6b1182507efac8a272fc309a79e22e58a5/tmux.1#L8715).
The [channel implementation](https://github.com/tmux/tmux/blob/94796f6b1182507efac8a272fc309a79e22e58a5/cmd-wait-for.c#L388)
retains an early signal until a waiter consumes it. Use a fresh channel name
for each operation.

</details>