New: epoll_wait(2): upper limit to timeout
https://bugzilla.kernel.org/show_bug.cgi?id=20762
Summary: epoll_wait(2): upper limit to timeout
Product: Documentation
Version: unspecified
Kernel Version: n/a
Platform: All
OS/Version: Linux
Tree: Mainline
Status: NEW
Severity: normal
Priority: P1
Component: man-pages
AssignedTo: documentation_man-pages-ztI5WcYan/[email protected]
ReportedBy: [email protected]
Regression: No
The timeout argument has an upper limit. Any values above that limit are treated the same as -1, i.e. to wait indefinitely. The limit is given by:
#define EP_MAX_MSTIMEO min(1000ULL * MAX_SCHEDULE_TIMEOUT / HZ, (LONG_MAX - 999ULL) / HZ)
That is, the limit depends on the size of a long and the timer frequency. Assuming the a long is never smaller than 32 bits and HZ never larger than 1000, the worst case is 35 minutes. I think this should be mentioned under "BUGS".
Although this is likely to be fixed in the future
(http://lkml.org/lkml/2010/8/8/144), the problem exists in at least 2.6.14 - 2.6.35. I don't know if select(2) and poll(2) are affected.
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[Bug 20762] epoll_wait(2): upper limit to timeout
In reply to a message not in the archivehttps://bugzilla.kernel.org/show_bug.cgi?id=20762
Michael Kerrisk <[email protected]> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|NEW |RESOLVED
CC| |[email protected]
Resolution| |CODE_FIX--- Comment #1 from Michael Kerrisk <[email protected]> 2012-08-16 09:33:31 --- I aplied the following patch:
man2/epoll_wait.2 +12 -0
@@ -198,6 +198,18 @@ If the new file descriptor becomes ready, it will cause the .BR epoll_wait () call to unblock. +.SH BUGS +In kernels before 2.6.37, a +.I timeout +value larger than approximately +.I LONG_MAX / HZ +milliseconds is treated as \-1 (i.e., infinity). +Thus, for example, on a system where the +.I sizeof(long) +is 4 and the kernel +.I HZ +value is 1000, +this means that timeouts greater than 35.79 minutes are treated as infinity. .SH "SEE ALSO" .BR epoll_create (2), .BR epoll_ctl (2),
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