[ECOS] Wake select() with a signal

[Jonathan Larmour]

Roland Caßebohm wrote:
 > On Friday, 1. November 2002 18:04, Roland Caßebohm wrote:
 >
 >> Hi everyone,
 >>
 >> I want to wake a waiting select by sending a signal to the thread.
 >>
 >> This does not always work. I think the reason is that the thread in
 >> which select() is call is not really sleeping all the time, even
 >> though it doesn't return. The pthread_kill() function respectively
 >> Cyg_Thread::release() only wakes a thread if the thread is sleeping.
 >> That makes sense, but what can I do if I want a waiting select() to
 >> return triggered from another thread?
 >>
 >
 > I just changed the select() function that it looks for the asr_pending
 > flag before it goes to sleep. I don't really think, that this is the
 > right solution, but in my case it works. Now the select() always
 > returns with errno=EINTR if the thread receives a signal.

Hmmm... Before the scheduler lock, the ASR should run. After the scheduler 
lock, nothing should be able to trigger an ASR to be scheduled; in 
particular nothing should be able to call pthread_kill. You're not calling 
pthread_kill from an ISR by any chance are you?

Oh, hold on, is it just that the pthread_kill is happening before the lock 
for the first time? If so, then I'm afraid that's tough - you could just 
as easily have pthread_kill'd it when the CPU was just making the call 
into the select function. From a programmatic point of view, that can just 
as easily happen. But your signal handler should definitely run 
regardless, or are you saying it doesn't do that either?

 > Does anybody know if the select() systemcall or every other systemcall
 > should always return if the thread receives a signal?

It should return if select() is actually waiting at the time.

Jifl
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