Hi List,
Reading current kernel git ipc/sem.c I see the following comment:
--
* - The previous code had two flaws:
...
* 2) It did not wake up all zero waiting processes. We try to do
* better but only get the semops right which only wait for zero or
* increase. If there are decrement operations in the operations
* array we do the same as before.
--
I have some questions about this comment.
Most importantly - does this mean that if I have multiple processes
queued inside semop() calls with sem_val = -1 (also, if it matters,
SEM_UNDO flag is set), I can expect to eventually see none of the
queued processes woken up when whoever has the semaphore releases it?
If that's the case, is there any semop best-use example I should be
following for multiple multi-threaded processes sharing multiple
semaphores?
Currently I have some globally reachable semaphores doing semop calls
with SEM_UNDO. They usually work fine with multiple processes waiting
on each other to lock the semaphore, but under certain circumstances a
semaphore will be released and none of the processes waiting on the
semaphore will be woken up.
Thanks in advance,
Tom Burns
Software Developer
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