What Progress is doing when it uses the futex() system call?

Posted by George Potemkin on 06-Feb-2017 13:48

OpenEdge 10.2B0832, Linux SUSE 11 SP3 64-bit

Session hung in the middle of transaction – its last notes before hang:


Proshut disconnect did not work. Session also ignored the signals (including SIGUSR1). Db activity of the session was not changing.

Linux strace command said:

Trace of process 27517 - /usr/dlc/bin/_progres [snip]
Process 27517 attached - interrupt to quit
futex(0x7fbd3952da54, FUTEX_WAIT_PRIVATE, 2, NULL


The futex() system call provides a method for waiting until a certain condition becomes true. It is typically used as a blocking construct in the context of shared-memory synchronization. When using futexes, the majority of the synchronization operations are performed in user space. A user-space program employs the futex() system call only when it is likely that the program has to block for a longer time until the condition becomes true. Other futex() operations can be used to wake any processes or threads waiting for a particular condition.

I guess the session was waiting for something that is NOT related to the database. What it can be?

Finally the session was killed using kill -9 and the database kept running:

[2017/02/03@18:22:25.810+0600] P-20614 T-140479547926272 I WDOG 8: (2527) Disconnecting dead user 195. 
[2017/02/03@18:22:25.810+0600] P-20614 T-140479547926272 I WDOG 195: (2252) Begin transaction backout. 
[2017/02/03@18:22:25.861+0600] P-20614 T-140479547926272 I WDOG 195: (2253) Transaction backout completed.

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Posted by gus bjorklund on 07-Feb-2017 09:06

futex’es are used by various functions in the C runtime library.

they are also used by various mutex functions in the posix thread library.

without the rest of the stack trace, we can’t tell what called it.

Posted by George Potemkin on 07-Feb-2017 11:12

Thnaks, Gus. So we can't guarantee the 100% safety when using kill -9 against a process in FUTEX_WAIT, can we?

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