Used pthread name functions returning result for FreeBSD and DragonFly

[YohDeadfall]

pthread_getname_np and pthread_setname_np received a wider adoption in past years and was added to:

• FreeBSD by June 11 2020 via 2ef84b7da9a6c3e23b4a135e6e863581f16d46e1,
• DargonFly by March 8 2021 via ab5dc9aceb34419d1c4b6006739e61acee8ee999.

There's not so much advantage except that the result can be checked in debug builds. Ideally it should be unified with Linux' implementation, but it trims the input.

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[ibraheemdev]

Is there any change here except the debug assertion? I'm not sure I see the benefit of this change, will it fail on older versions of FreeBSD/DragonFly?

[YohDeadfall]

While pthread_setname_np isn't well standardized (the np suggests that) and was supported only by GNU originally, there's a movement to make it more portable. NuttX supports it too, but it will take some time to land it in the libc crate.

Yes, it will fail on non-maintained versions of FreeBSD/DragonFly, but:

• the oldest version FreeBSD maintains is 13, and it already has the function in it (source);
• for DragonFlyBSD the function is included into 6.0.0 (source), and any prior versions are unmaintained.

I would unify the code between Linux GNU, DragonFlyBSD and FreeBSD, but there's a small implementation difference. The Linux kernel requires thread names being no longer than 16 bytes including a null terminator. Otherwise, it returns an error. Other platforms just truncate the provided name.

rust/library/std/src/sys/pal/unix/thread.rs

Lines 137 to 141 in 9200cbc

	// Available since glibc 2.12, musl 1.1.16, and uClibc 1.0.20.
	let name = truncate_cstr::<{ TASK_COMM_LEN }>(name);
	let res = libc::pthread_setname_np(libc::pthread_self(), name.as_ptr());
	// We have no good way of propagating errors here, but in debug-builds let's check that this actually worked.
	debug_assert_eq!(res, 0);

[ibraheemdev]

I see, but the only difference between the FreeBSD/DragonFly and OpenBSD/NuttX code is the debug assertion? So the idea here is to assert that the call is valid on FreeBSD and DragonFly?

[YohDeadfall]

Yes, a bit of safety in debug builds instead of having muted errors.