Eric Dumazet wrote:So please how do you guarantee that thread 1 runs *before* thread 2)
Your program is racy and have undefined behavior.
A thread should not close a handle 'used by another thread blocked in a sytemcall'
The race is : if a thread does a close(fd), then the fd value may be reused by another thread during an open()/socket()/dup()... syscall, and the first thread could issue the select() syscall (or read()/write()/...) on the bad file.
Apologies, but I don't follow this.
It was my understanding that the (potentially) many threads of a single process all share a canonical file descriptor table. Hence as long as the various calls you mention are issued in a guaranteed order, maintaining state as you go (which is what the 1 second sleep in the test code was a very quick and dirty way to almost do), I don't see how a race condition arises.
If I were to replace the sleep (1) with, say a global semaphore or something similar, would your explanation still hold?
Andre Ben Hamou
Imperial College London