Filesystem: get_pids() "safe": scan /proc only once #1978
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Caution: advanced shell trickery. With many processes, scanning /proc can take significant time. Use only one find /proc, feed /proc/**/maps to grep via fifo and xargs, and send matching symlinks to stdout directly. On a "busy" system, this cuts the time for get_pids() almost in half.
oalbrigt
reviewed
Sep 19, 2024
| D=$(mktemp -d "$HA_RSCTMP/Filesystem.get_pids.safe.XXXXXX") | ||
| mkfifo "$D/maps" | ||
| ( | ||
| < "$D/maps" xargs -r grep -l " $dir/" | cut -d/ -f3 | uniq & |
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xargs on BSD doesnt have the -l parameter.
FreeBSD manpage: https://man.freebsd.org/cgi/man.cgi?query=xargs
Manpage with POSIX-supported parameters: https://pubs.opengroup.org/onlinepubs/9699919799/utilities/xargs.html
oalbrigt
reviewed
Sep 19, 2024
| # we can remove the tmpdir and fifo early | ||
| rm -rf "$D" | ||
| find /proc -path '/proc/[!0-9]*' -prune -o \ | ||
| -type f -name maps -fprint /dev/fd/3 -o \ |
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-fprint is GNU findutils only.
POSIX manpage: https://pubs.opengroup.org/onlinepubs/9699919799/utilities/find.html
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-lname is not supported by POSIX, but available on *BSD as compatibility option, so no need to worry about that parameter.
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Caution: advanced shell trickery.
With many processes, scanning /proc can take significant time. Use only one find /proc, feed /proc/**/maps to grep via fifo and xargs, and send matching symlinks to stdout directly.
On a "busy" system, this cuts the time for get_pids() almost in half.