Messages in this thread | | | Date | Fri, 04 Sep 2009 17:26:35 -0400 | From | Mike Heffner <> | Subject | HR timers prevent an itimer from generating EINTR? |
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Summary:
Mixing HR timers with itimers occasionally hides an EINTR from a blocking syscall.
Description:
In my test program I have a High Resolution timer firing every one second (with SA_RESTART) and I set an itimer (without SA_RESTART) to fire after three seconds. I then execute a blocking system call (flock in this case) and expect the three second itimer to interrupt the system call with EINTR. However, I frequently notice that the itimer will fire but it will not interrupt the blocking system call. There appears to be a race between the HR timer firing and the itimer firing. If I offset the HR timer frequency by a half second, the itimer always interrupts the system call.
Kernel version:
These kernels both demonstrate the condition:
2.6.29.6-217.2.16.fc11.x86_64 and 2.6.30.5-43.fc11.x86_64
I do not see this condition on:
2.6.18-53.el5
Test program:
The following program illustrates this condition:
http://github.com/mheffner/scripts/commits/master/hrtimer_vs_itimer.c
Is this behavior expected?
Cheers,
Mike
--
Mike Heffner <mikeh@fesnel.com>
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