xspawn: Wrap the real posix_spawn() if possible

[tavianator]

Benchmark results

Process spawning

linux v6.5

One file per process

Command	Mean [s]	Min [s]	Max [s]	Relative
bfs bench/corpus/linux -maxdepth 2 -exec true -- {} \;	1.385 ± 0.012	1.364	1.398	4.07 ± 0.18
bfs-main bench/corpus/linux -maxdepth 2 -exec true -- {} \;	1.578 ± 0.013	1.556	1.602	4.64 ± 0.21
bfs-posix-spawn bench/corpus/linux -maxdepth 2 -exec true -- {} \;	1.150 ± 0.011	1.124	1.164	3.38 ± 0.15
find bench/corpus/linux -maxdepth 2 -exec true -- {} \;	1.475 ± 0.019	1.446	1.496	4.33 ± 0.20
fd -u --search-path bench/corpus/linux --max-depth=2 -x true --	0.340 ± 0.015	0.316	0.365	1.00
fd -j1 -u --search-path bench/corpus/linux --max-depth=2 -x true --	1.142 ± 0.021	1.110	1.165	3.36 ± 0.16

Many files per process

Command	Mean [ms]	Min [ms]	Max [ms]	Relative
bfs bench/corpus/linux -exec true -- {} +	71.8 ± 2.1	66.3	76.1	1.00
bfs-main bench/corpus/linux -exec true -- {} +	73.2 ± 1.3	69.6	75.7	1.02 ± 0.03
bfs-posix-spawn bench/corpus/linux -exec true -- {} +	157.8 ± 2.0	154.0	161.8	2.20 ± 0.07
find bench/corpus/linux -exec true -- {} +	262.3 ± 2.4	260.0	268.6	3.65 ± 0.11
fd -u --search-path bench/corpus/linux -X true --	314.4 ± 5.5	305.7	321.3	4.38 ± 0.15

Spawn in parent directory

Command	Mean [ms]	Min [ms]	Max [ms]	Relative
bfs bench/corpus/linux -maxdepth 3 -execdir true -- {} +	844.1 ± 9.4	833.9	865.1	1.75 ± 0.04
bfs-main bench/corpus/linux -maxdepth 3 -execdir true -- {} +	913.2 ± 19.4	873.8	951.0	1.89 ± 0.05
bfs-posix-spawn bench/corpus/linux -maxdepth 3 -execdir true -- {} +	483.5 ± 9.1	467.8	500.8	1.00
find bench/corpus/linux -maxdepth 3 -execdir true -- {} +	1115.6 ± 17.9	1091.0	1151.1	2.31 ± 0.06

Details

Versions

$ bfs --version | head -n1
bfs 3.0.4
$ bfs-main --version | head -n1
bfs 3.0.4-43-gb2ab7a15
$ bfs-posix-spawn --version | head -n1
bfs 3.0.4-49-g7d69fef6
$ find --version | head -n1
find (GNU findutils) 4.9.0
$ fd --version
fd 8.7.1

[codecov]

Codecov Report

Attention: 53 lines in your changes are missing coverage. Please review.

Files	Coverage Δ
src/ctx.c	81.39% <50.00%> (-0.15%)	⬇️
src/eval.c	72.16% <92.85%> (+0.61%)	⬆️
src/bfstd.c	74.60% <64.28%> (-4.28%)	⬇️
src/exec.c	72.55% <70.00%> (-0.30%)	⬇️
src/xspawn.c	20.96% <36.50%> (-37.64%)	⬇️

... and 2 files with indirect coverage changes

📢 Thoughts on this report? Let us know!.

[tavianator]

There is a surprising perf regression for -exec ... {} +, but IMO the benefits outweigh it. It seems like either the kernel or glibc's fault anyway, and ought to be fixed there.

This also works around google/sanitizers#1699. Hopefully no more CI timeouts!