On Mon, 11 Dec 2006, Arne H. Juul wrote: Looking at the Java VM source code it does some tricks with dup2() to reopen the close()'d filedescriptor, making it point to a filedescriptor that's pre-connected to a closed socket.

A small C program that duplicates this (using pipes to make it a bit simpler) follows. I'm not sure if any standards demand that this works like it used to on FreeBSD 4 / libc_r, but since Java uses it it would be really nice if this could be made to work in FreeBSD 6 (libthr and libpthread). Or maybe somebody has another suggestions on how to implement the Java close() semantics?

Anyway, the following C program works as intended on FreeBSD 4, hangs on FreeBSD 6 (amd64), compiled with: cc -Wall -pthread read_dup2.c -o read_dup2

#include <fcntl.h> #include <stdlib.h> #include <stdio.h> #include <unistd.h> #include <pthread.h>

int p[2];

void *run(void *arg) { ssize_t res; char tmp[128]; fprintf(stderr, "reading...\n"); res = read(p[0], tmp, sizeof(tmp)); fprintf(stderr, "read result: %d\n", (int)res); if (res < 0) { perror("read"); } return arg; }

int main(int argc, char **argv) { pthread_t t; int d = open("/dev/null", O_RDONLY); if (pipe(p) != 0) { perror("pipe"); return 1; } if (pthread_create(&t, NULL, run, NULL) != 0) { perror("thread create"); return 1; } sleep(1); d = open("/dev/null", O_RDONLY); if (d < 0) { perror("open dev null"); exit(1); } if (dup2(d, p[0]) < 0) { perror("dup2"); exit(1); } if (pthread_join(t, NULL) != 0) { perror("thread join"); exit(1); } return 0; }