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Speed up close_fds with the new close_range() Linux/FreeBSD syscall #189

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#255
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Speed up close_fds with the new close_range() Linux/FreeBSD syscall#189
#255
@nh2

Description

@nh2
nh2
opened on Aug 12, 2020

Background:

As written in

process/System/Process/Common.hs

Line 91 in cb1d1a6

close_fds :: Bool, -- ^ Close all file descriptors except stdin, stdout and stderr in the new process (on Windows, only works if std_in, std_out, and std_err are all Inherit). This implementation will call close an every fd from 3 to the maximum of open files, which can be slow for high maximum of open files.

This implementation will call close() an every fd from 3 to the maximum of open files, which can be slow for high maximum of open files.

The new close_range() syscall solves this, closing them all in 1 go. According to the LWN link, it is very fast, and you can give it MAXINT.

The code that needs to be augmented (with CPP):

process/cbits/posix/runProcess.c

Lines 255 to 273 in cb1d1a6

if (close_fds) {
int i;
if (max_fd == 0) {
#if HAVE_SYSCONF
max_fd = sysconf(_SC_OPEN_MAX);
if (max_fd == -1) {
max_fd = 256;
}
#else
max_fd = 256;
#endif
}
// XXX Not the pipe
for (i = 3; i < max_fd; i++) {
if (i != forkCommunicationFds[1]) {
close(i);
}
}
}

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