Synchronization problem with posix_spawn
Wed Jul 29 23:12:50 GMT 2020
On 7/29/2020 4:17 PM, Ken Brown via Cygwin wrote:
> posix_spawn(p) returns before the spawned process is fully up and running. As a
> result, the spawned process can fail to receive signals. The attached test case
> illustrates the problem. It spawns a sleep process and then tries to kill it.
> On exit, the sleep process is still running.
> The following excerpts from the strace output show the issue: The SIGTERM signal
> is sent after the main program has forked a subprocess (and posix_spawnp has
> returned), but before the forked subprocess has exec'd the sleep process:
> 559 32069 [main] spawn_test 4125 vfork: stub called
> 257 48437 [main] spawn_test 4125 dofork: 4126 = fork()
> 754 9511 [main] spawn_test 4126 dofork: 0 = fork()
> 66 48503 [main] spawn_test 4125 kill0: kill (4126, 15)
> 44 9555 [main] spawn_test 4126 find_exec: find_exec (/usr/bin/sleep)
> 42 10835 [main] spawn_test 4126 spawnve: spawnve (/usr/bin/sleep, sleep,
> 45 3149 [main] sleep 4126 child_info::ready: signalled 0x164 that I was
> 6475 21055 [main] spawn_test 4126! child_info::sync: pid 45028, WFMO
> returned 0, exit_code 0x103, res 1
> --- Process 45028 (pid: 4126) thread 41444 created
I just took a look at the source, and I see that posix_spawn was taken from
FreeBSD. Does FreeBSD have the same problem? Should applications just be aware
of this issue and insert a sleep after posix_spawn before sending signals?
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