Condition variable blocks when changing time

[Johan Borkhuis <johan@…>]

I am using Linux on an ARM system, running Boost 1.47. My application needs accurate timing, and for this I use a POSIX timer using SIGRTMIN. This part is not something that I can control, it is an external library that implements this. I use condition variables as a timing mechanism within my software.

When I use condition variables without the POSIX timer there is no problem. The timing continues correctly, even if I change the time forward or backward.

When I start the POSIX timer the condition variable does not time-out when I change the time backward. It only times out when the original time (plus timeout) is reached.

When I changed the clock of the pthread condition variable to monotonic (call to pthread_condattr_setclock(&condattr, CLOCK_MONOTONIC)) the result was OK again.

Attached is a test application that shows the problem and implements a solution. This solution is not within the Boost library but directly as a POSIX condition variable. Options to the test application:

-b: use boost condition variable
-s: generate POSIX signals

When running the testapplication with -bs the application will stop reporting when the time is changed backwards. When the time is set back to a time after the time the time was changed the application will continue.

[Johan Borkhuis <johan@…>]

Demo application showing the problem

[anonymous]

I also have the same issue.

[viboes]

Boost.Thread provides timed functions based on a Boost.Chrono. Using the steady_clock should solve your problem. The legacy time-based functions will be deprecated soon. Please let me know if this solves your problem.

[viboes]

I'm writing a patch that uses pthread_condattr_setclock. As I said I have no platform providing it (I'm using MacOS). The user will need to define BOOST_THREAD_HAS_CONDATTR_SET_CLOCK_MONOTONIC until I find a way to detect it.

Is there any one that can test it?

[viboes]

Add to develop branch ​https://github.com/boostorg/thread/commit/9f883f6ad7377b88b79fa70cc5de68cbfb0213e4

[viboes]

Please, could you try the develop branch

​https://github.com/boostorg/thread/commit/8f5de1d7c34ff7248261874f273498a622bf76d4

[viboes]

​https://github.com/boostorg/thread/commit/730cb550e6d969520c3f39e0ddf5d80351bddf3a