How to limit the execution time of a function in C/POSIX?

Question

Similar to this question, I'd like to limit the execution time of a function--preferably with microsecond accuracy--in C. I imagine that C++ exceptions could be used to achieve a result similar to this Python solution. Though it's not ideal, such an approach is wholly unavailable in plain C.

I wonder, then, how might I interrupt the execution of a function after a certain time interval in C on a Posix system? For relatively simple situations a bit of silly business works just fine, but that adds a fair amount of code orthogonal to the problem solution. Let's say I have a function like so:

void boil(egg *e) {
    while (true)
    do_boil(e);
}

I want to run run boil on an egg*, interrupting it every 50μs to check do something like so:

egg *e = init_egg();
while (true) {
    preempt_in(50, (void) (*boil), 1, e);
    /* Now boil(e) is executed for 50μs, 
       then control flow is returned to the
       statement prior to the call to preempt_in.
     */
    if (e->cooked_val > 100)
        break;
}

I realize that pthreads could be used to do this, but I'm rather more interested in avoiding their use. I could switch between ucontext_t's in a SIGALRM handler, but the POSIX standard notes that the use of setcontext/swapcontext is not to be used in a signal handler and, indeed, I note differing behaviors between Linux and Solaris systems when doing so.

Is this effect possible to achieve? If so, in a portable manner?

Answer 1

You can either use threads, or have the function poll a timer (or a global variable set by SIGALRM handler), then save its state and exit when the allotted time has expired. Use of ucontext_t is deprecated and should never be used in new code, at all, much less from signal handlers.

Answer 2

The solution I desire suddenly occurs to me: goto! I'll setup a jump point just after the function I wish to limit, set a timer and in the signal handler which deals with the SIG*ALRM simply jump to the instruction after the function.