mq_timedreceive and changing the real time clock

Tim Potter

We are using Linux 3.12.10 from SDK 7. We have noticed some odd behavior when adjusting the clock. We are using mq_timedreceive() to wait on messages on a queue. The wait time makes use of an absolute time. When we simulate daylight savings and adjust the clock back an hour we see that our process hangs. Does the mq_timedreceive automatically adjust to wait time to reflect the time change in the real time clock?

over 10 years ago

0 Cvetolin Shulev-XID over 10 years ago

TI__Guru 65405 points

Hi Tim,

There is a link to mq_timedreceive() description and short example:
www.qnx.com/.../mq_timedreceive.html
Do your mq_timedreceive() usage matching to description at the link?

BR
Tsvetolin Shulev

0 Cvetolin Shulev-XID over 10 years ago in reply to Cvetolin Shulev-XID

TI__Guru 65405 points

Tim,

The mq_timedreceive() function receives the oldest of the highest priority messages in the queue specified by mqdes. Therefore if you adjust the system clock back a hour the oldest message will be different. In case of making system clock adjustment is recommended to use mq_timedreceive_monotonic() function because it uses CLOCK_MONOTONIC.
You can find more detail at:
www.qnx.com/.../index.jsp

BR
Tsvetolin Shulev

0 Tim Potter over 10 years ago in reply to Cvetolin Shulev-XID

Intellectual 726 points

Ah! I was not aware of the mq_timedreceive_monotonic(). If that is available in SDK 7 that will solve the issue. Thanks!

0 Brad Griffis over 10 years ago in reply to Tim Potter

TI__Guru*** 125430 points

That function exists only in Neutrino. An alternate solution is given here:

http://stackoverflow.com/questions/33873374/pthreads-mq-timedreceive-pthread-cond-timedwait-and-clock-realtime

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mq_timedreceive and changing the real time clock