signals/nonreentrant.c

/* nonreentrant.c

   Demonstrate the nonreentrant nature of some library functions, in this
   example, crypt(3).
*/
#if ! defined(_XOPEN_SOURCE) || _XOPEN_SOURCE < 600
#define _XOPEN_SOURCE 600
#endif
#include <unistd.h>
#include <signal.h>
#include <string.h>
#include <crypt.h>
#include "tlpi_hdr.h"

static char *str2;                  /* Set from argv[2] */
static volatile int handled = 0;    /* Counts number of calls to handler */

static void
handler(int sig)
{
    crypt(str2, "xx");
    handled++;
}

int
main(int argc, char *argv[])
{
    char *cr1;
    int callNum, mismatch;
    struct sigaction sa;

    if (argc != 3)
        usageErr("%s str1 str2\n", argv[0]);

    str2 = argv[2];                      /* Make argv[2] available to handler */
    cr1 = strdup(crypt(argv[1], "xx"));  /* Copy statically allocated string
                                            to another buffer */
    if (cr1 == NULL)
        errExit("strdup");

    sigemptyset(&sa.sa_mask);
    sa.sa_flags = 0;
    sa.sa_handler = handler;
    if (sigaction(SIGINT, &sa, NULL) == -1)
        errExit("sigaction");

    /* Repeatedly call crypt() using argv[1]. If interrupted by a
       signal handler, then the static storage returned by crypt()
       will be overwritten by the results of encrypting argv[2], and
       strcmp() will detect a mismatch with the value in 'cr1'. */

    for (callNum = 1, mismatch = 0; ; callNum++) {
        if (strcmp(crypt(argv[1], "xx"), cr1) != 0) {
            mismatch++;
            printf("Mismatch on call %d (mismatch=%d handled=%d)\n",
                    callNum, mismatch, handled);
        }
    }
}