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document race condition caused by queueing of multiple events

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leitner 2016-10-01 20:10:38 +00:00
parent 3039d04915
commit 8913f6174c
2 changed files with 24 additions and 0 deletions
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12
io/io_wait.3
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@ -23,5 +23,17 @@ io_wait is not interrupted by the delivery of a signal. Programs that
expect interruption are unreliable: they will block if the same signal expect interruption are unreliable: they will block if the same signal
is delivered a moment before io_wait. The correct way to handle signals is delivered a moment before io_wait. The correct way to handle signals
is with the self-pipe trick. is with the self-pipe trick.
.SH NOTE
Depending on the underlying operating system primitive, there is a
potential race condition to be aware of. Some event notification
mechanisms (for example, kqueue on BSD and epoll on Linux) will return
multiple events. If your application operates on pairs of file
descriptors (a proxy server maybe), and an error on one descriptor
can lead to closing the other descriptor, then an outstanding event on
the other descriptor can still be queued for delivery to you. Be
prepared to receive events for a descriptor that has already been
closed.
.SH "SEE ALSO" .SH "SEE ALSO"
io_waituntil(3), io_check(3), io_wantread(3), io_wantwrite(3), io_fd(3) io_waituntil(3), io_check(3), io_wantread(3), io_wantwrite(3), io_fd(3)

12
io/io_waituntil.3
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@ -7,5 +7,17 @@ io_waituntil \- wait for events
void \fBio_waituntil\fP(tai6464 t); void \fBio_waituntil\fP(tai6464 t);
.SH DESCRIPTION .SH DESCRIPTION
io_waituntil(t) is like io_wait() but does not wait (noticeably) past time \fIt\fR. io_waituntil(t) is like io_wait() but does not wait (noticeably) past time \fIt\fR.
.SH NOTE
Depending on the underlying operating system primitive, there is a
potential race condition to be aware of. Some event notification
mechanisms (for example, kqueue on BSD and epoll on Linux) will return
multiple events. If your application operates on pairs of file
descriptors (a proxy server maybe), and an error on one descriptor
can lead to closing the other descriptor, then an outstanding event on
the other descriptor can still be queued for delivery to you. Be
prepared to receive events for a descriptor that has already been
closed.
.SH "SEE ALSO" .SH "SEE ALSO"
io_wait(3), io_check(3), io_wantread(3), io_wantwrite(3), io_fd(3) io_wait(3), io_check(3), io_wantread(3), io_wantwrite(3), io_fd(3)