std.os.linux: remove app_mask and block&unblock pair in raise

[ruihe774]

I believe the order of first two u32 is wrong.

See also: https://github.com/bminor/musl/blob/master/src/signal/sigfillset.c

[alexrp]

The reason musl special-cases SIGTIMER (32), SIGCANCEL (33), and SIGSYNCCALL (34) is that they're used in the implementation of pthread and timer APIs in musl.

The libc-less version of Zig's standard library does not use these signal numbers for anything, and the app_mask and all_mask constants are only used in the Linux implementations of raise() and abort() in std.posix when libc is not linked.

I'm inclined to say that, rather than adjusting app_mask, it should just be deleted in favor of using all_mask in raise() instead. But maybe there's some factor I'm missing here. cc @andrewrk since these constants were added in 6f1a7a0.

[ruihe774]

I'm wondering why raise() need to block and unblock signals. musl does this, but glibc does not. I think we can remove the block&unblock pair.

[alexrp]

musl does this, but glibc does not. I think we can remove the block&unblock pair.

Maybe. I'd still like Andrew's thoughts on this before we go ahead with that change.

[alexrp]

Also, perhaps the same would be true of abort()?

[ruihe774]

Also, perhaps the same would be true of abort()?

Current implementation of abort() first uses raise() then goes through the block/unblock pair. I guess in most cases (no user-installed handler) the process will just terminate at the first raise(). If it is not, it is necessary to use the block/unblock pair and reset the signal handler when all signals are blocked to avoid race condition.