Date: Wed, 2 Dec 2009 19:56:47 +0300 From: Gennady Proskurin <gprspb@mail.ru> To: freebsd-threads@freebsd.org Subject: pipe with threads Message-ID: <20091202165647.GA1944@gpr.nnz-home.ru>
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--h31gzZEtNLTqOjlF Content-Type: text/plain; charset=us-ascii Content-Disposition: inline I use usual scenario for writing data to stdin of some other program: 1. pipe, fork 2. Child: dup2, exec. Parent: write When my program is single-threaded (or may be multithreaded, with only one thread running this scenario), all works fine. But when this scenario executed concurently by many threads, the reading process sometimes doesn't see, that pipe was closed and reading process is stuck in read() (piperd wchan), and write process is stuck in waitpid. Is it a bug somewhere or I missing something? Test program attached. I compile it with "cc -o pipetest pipetest.c -pthread" And run: "while [ 1 ]; do ./pipetest ; done" My system: fresh 9-currend/amd64, smp (2 CPU) --h31gzZEtNLTqOjlF Content-Type: text/plain; charset=us-ascii Content-Disposition: attachment; filename="pipetest.c" #include <stdio.h> #include <unistd.h> #include <signal.h> #include <sys/wait.h> #include <pthread.h> static char data[10]; void* thr_func(void* arg) { int pipe_fd[2]; int pid; const char* buf = data; int write_remain = sizeof(data); int waitpid_status; int waitpid_res; int bar_res; if (pipe(pipe_fd)<0) { perror("pipe()"); _exit(1); } printf("fd: %i %i\n", pipe_fd[0], pipe_fd[1]); pid = fork(); switch(pid) { case -1: perror("fork()"); _exit(1); case 0: if (close(pipe_fd[1])) { perror("close()"); _exit(1); } if (dup2(pipe_fd[0], STDIN_FILENO) == -1) { perror("dup2()"); _exit(1); } execl("/bin/sh", "sh", "-c", "cat > /dev/null", 0); perror("exec()"); _exit(1); } if (close(pipe_fd[0])) { perror("close()"); _exit(1); } // write data while (write_remain>0) { int w = write(pipe_fd[1], buf, write_remain); if (w>0) { buf += w; write_remain -= w; printf("write:%i\n", w); } else { perror("write()"); _exit(1); } } if (close(pipe_fd[1])) { perror("close()"); _exit(1); } // wait child waitpid_res = waitpid(pid, &waitpid_status, 0); if (waitpid_res != pid) { perror("waitpid()"); _exit(1); } return 0; } int main() { pthread_t thr1, thr2; sigset_t mask; // block SIGCHLD sigemptyset(&mask); sigaddset(&mask, SIGCHLD); if (sigprocmask(SIG_BLOCK, &mask, 0)) { perror("sigprocmask()"); _exit(1); } // create threads if (pthread_create(&thr1,0,thr_func,0) || pthread_create(&thr2,0,thr_func,0)) { perror("pthread_create()"); _exit(1); } // join threads if (pthread_join(thr1,0) || pthread_join(thr2,0)) { perror("pthread_join()"); _exit(1); } printf("OK\n"); return 0; } --h31gzZEtNLTqOjlF--
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