Message-ID: <4FC9391B.3040104@etr-usa.com>
Date: Fri, 01 Jun 2012 15:50:19 -0600
From: Warren Young <warren@etr-usa.com>
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To: Cygwin-L <cygwin@cygwin.com>
Subject: Re: How to "bisect" Cygwin?
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On 6/1/2012 1:51 PM, Ryan C. Underwood wrote:
> On Fri, Jun 01, 2012 at 08:59:06PM +0200, Corinna Vinschen wrote:
>
>> If you can press a long story into a short testcase in plain C with the
>> bare minimum of code to reproduce the behaviour, it would be much
>> appreciated.
>
> The basic issue is that sem_wait() is being kicked out with EINTR
> extremely frequently (9 out of 10 times or more),

Does the attached program vaguely resemble what your program is trying 
to do?  It does get EINTR, but only because I'm using alarm(2) to add a 
timeout to the sem_wait() call.

You should just get an infinite series of "Child timed out normally 
waiting for the semaphore." messages from it after initialization, one 
per second.

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#include <semaphore.h>
#include <sys/types.h>

#include <errno.h>
#include <fcntl.h>
#include <signal.h>
#include <stdio.h>
#include <stdlib.h>

static int timed_out = 0;

void timeout(int sig)
{
	timed_out = 1;
}

int main()
{
	static const char* sem_name = "/myhappysemaphore";
	sem_t* ps = sem_open(sem_name, O_RDWR);
	if (ps) sem_close(ps);	// clean up old semaphore; we probably crashed
	ps = sem_open(sem_name, O_CREAT, 0600, 0);
	if (ps == SEM_FAILED) {
		perror("sem_open");
		return 1;
	}
	puts("Created semamphore.");

	pid_t pid = fork();
	switch (pid) {
		case -1:	// error
			perror("fork");
			return 2;

		case 0:		// child
			signal(SIGALRM, timeout);
			while (1) {
				alarm(1);
				int ret = sem_wait(ps);
				if (ret == -1) {
					if (timed_out) {
						if (errno == EINTR) {
							puts("Child timed out normally waiting "
									"for the semaphore.");
							timed_out = 0;
						}
						else {
							puts("Child timed out ABNORMALLY waiting "
									"for the semaphore!");
							exit(99);
						}
					}
					else {
						perror("sem_wait");
						exit(69);
					}
				}
				else {
					puts("Child got the semaphore!  "
							"How the spit did that happen?");
					exit(42);
				}
			}
			break;

		default: {	// parent
			puts("Created child.  Posting the deathwatch.");
			int status;
			while (1) {
				pid_t ret = waitpid(pid, &status, 0);
				if (ret > 0) {
					if (WIFEXITED(status)) {
						printf("Child %d died peacefully, code %d.\n",
								ret, WEXITSTATUS(status));
						break;
					}
					else {
						printf("Child %d died screaming, status 0x%08X.\n",
								ret, status);
						return 3;
					}
				}
				else {
					perror("waitpid");
					return 4;
				}
			}
		}
	}

	return 0;
}


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