Add support for attaching profiler to a PID (Linux only). #18
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-p will be used for the newly added --pid option. Unfortunately this is a breaking change, but this allows the command line to be consistent with perf.
Previously the profiler only terminated on process exit, but with PID attach we need to stop it on user request. Allow passing-in an AtomicBool as a stop flag.
For now, support this for Linux only since on macOS hooking stuff complicates attaching.
mstange
approved these changes
Jan 28, 2023
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| // When the first Ctrl+C is received, stop recording. | ||
| // The server launches after the recording finishes. On the second Ctrl+C, terminate the server. | ||
| let stop = Arc::new(AtomicBool::new(false)); | ||
| #[cfg(unix)] | ||
| signal_hook::flag::register_conditional_default(signal_hook::consts::SIGINT, stop.clone()) | ||
| .expect("cannot register signal handler"); | ||
| #[cfg(unix)] | ||
| signal_hook::flag::register(signal_hook::consts::SIGINT, stop.clone()) | ||
| .expect("cannot register signal handler"); |
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I think I've understood how this works, but it feels a bit non-obvious. It looks like register_conditional_default uses the AtomicBool as an input, whereas register uses it as an output. So on the first Ctrl+C, the first signal handler reads false and doesn't act, and the second signal handler writes true. Then on the second Ctrl+C, the first signal handler reads true and terminates. So the order of setting these handlers also matters.
I'll land this as-is, but I'm open for suggestions to make this easier to read.
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This adds support for attaching to a PID by
samply record -p 12345.I only implemented (and feature flagged) this for Linux, since the attaching story seems more complicated on the macOS side.