Using sigprocmask to implement locks
- by EpsilonVector
I'm implementing user threads in Linux kernel 2.4, and I'm using ualarm to invoke context switches between the threads.
We have a requirement that our thread library's functions should be uninterruptable, so I looked into blocking signals and learned that using sigprocmask is the standard way to do this.
However, it looks like I need to do quite a lot to implement this:
sigset_t new_set, old_set;
sigemptyset(&new_set);
sigaddset(&new_set, SIGALRM);
sigprocmask(SIG_BLOCK, &new_set, &old_set);
This blocks SIGALARM but it does this with 3 function invocations! A lot can happen in the time it takes for these functions to run, including the signal being sent.
The best idea I had to mitigate this was temporarily disabling ualarm, like this:
sigset_t new_set, old_set;
time=ualarm(0,0);
sigemptyset(&new_set);
sigaddset(&new_set, SIGALRM);
sigprocmask(SIG_BLOCK, &new_set, &old_set);
ualarm(time, 0);
Which is fine except that this feels verbose. Isn't there a better way to do this?
