#include <stdio.h>
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#include <errno.h>
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#include <stdlib.h>
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#include <unistd.h>
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#include <sys/wait.h>
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#include <sys/mman.h>
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#include <sys/syscall.h>
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#include <linux/futex.h>
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#include <sys/time.h>
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#include "usg_common.h"
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#include <sys/mman.h>
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#include <sys/stat.h> /* For mode constants */
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#include <fcntl.h> /* For O_* constants */
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#include "sem_util.h"
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#include "sem_util.h"
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int _get(key_t key, unsigned int value) {
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// printf("==================_get===============================\n");
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int semid, perms;
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perms = S_IRUSR | S_IWUSR;
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semid = semget(key, 1, IPC_CREAT | IPC_EXCL | perms);
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if (semid != -1) { /* Successfully created the semaphore */
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union semun arg;
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struct sembuf sop;
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//logger.info("%ld: created semaphore\n", (long)getpid());
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arg.val = 0; /* So initialize it to 0 */
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if (semctl(semid, 0, SETVAL, arg) == -1)
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err_exit(errno, "semctl 1");
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//logger.info("%ld: initialized semaphore\n", (long)getpid());
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/* Perform a "no-op" semaphore operation - changes sem_otime
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so other processes can see we've initialized the set. */
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sop.sem_num = 0; /* Operate on semaphore 0 */
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sop.sem_op = value;
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sop.sem_flg = 0;
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if (semop(semid, &sop, 1) == -1)
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err_exit(errno, "semop");
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//logger.info("%ld: completed dummy semop()\n", (long)getpid());
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} else { /* We didn't create the semaphore set */
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if (errno != EEXIST) { /* Unexpected error from semget() */
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err_exit(errno, "semget 1");
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} else { /* Someone else already created it */
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const int MAX_TRIES = 10;
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int j;
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union semun arg;
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struct semid_ds ds;
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semid = semget(key, 1, perms); /* So just get ID */
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if (semid == -1)
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err_exit(errno, "semget 2");
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// logger.info("%ld: got semaphore key\n", (long)getpid());
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/* Wait until another process has called semop() */
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arg.buf = &ds;
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for (j = 0; j < MAX_TRIES; j++) {
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//logger.info("Try %d\n", j);
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if (semctl(semid, 0, IPC_STAT, arg) == -1)
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err_exit(errno, "semctl 2");
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if (ds.sem_otime != 0) /* Semop() performed? */
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break; /* Yes, quit loop */
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sleep(1); /* If not, wait and retry */
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}
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if (ds.sem_otime == 0) /* Loop ran to completion! */
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err_exit(errno, "Existing semaphore not initialized");
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}
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}
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return semid;
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}
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/* Reserve semaphore (blocking), return 0 on success, or -1 with 'errno'
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set to EINTR if operation was interrupted by a signal handler */
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/* Reserve semaphore - decrement it by 1 */
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int _dec(int semId) {
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struct sembuf sops;
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sops.sem_num = 0;
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sops.sem_op = -1;
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sops.sem_flg = SEM_UNDO;
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while (semop(semId, &sops, 1) == -1)
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if (errno != EINTR) {
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// err_msg(errno, "_dec");
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return errno;
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}
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return 0;
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}
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int _dec_nowait(int semId) {
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struct sembuf sops;
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sops.sem_num = 0;
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sops.sem_op = -1;
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sops.sem_flg = IPC_NOWAIT ;
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while (semop(semId, &sops, 1) == -1)
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if (errno != EINTR) {
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// err_msg(errno, "_dec_nowait");
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return errno;
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}
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return 0;
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}
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int _dec_timeout(const int semId, const struct timespec *timeout) {
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struct sembuf sops;
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sops.sem_num = 0;
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sops.sem_op = -1;
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sops.sem_flg = 0;
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while (semtimedop(semId, &sops, 1, timeout) == -1)
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if (errno != EINTR) {
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// err_msg(errno, "_dec_timeout");
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return errno;
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}
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return 0;
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}
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/**
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* If sem_op equals 0, the value of the semaphore is checked to see whether it
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* currently equals 0. If it does, the operation completes immediately; otherwise,
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* semop() blocks until the semaphore value becomes 0.
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*/
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int _zero(int semId) {
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// logger.debug("%d: _dec\n", semId);
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struct sembuf sops;
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sops.sem_num = 0;
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sops.sem_op = 0;
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sops.sem_flg = 0;
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while (semop(semId, &sops, 1) == -1)
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if (errno != EINTR) {
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// err_msg(errno, "_zero");
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return errno;
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}
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return 0;
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}
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int _zero_nowait(int semId) {
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struct sembuf sops;
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sops.sem_num = 0;
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sops.sem_op = 0;
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sops.sem_flg = IPC_NOWAIT;
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while (semop(semId, &sops, 1) == -1)
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if (errno != EINTR) {
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// err_msg(errno, "_zero_nowait");
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return errno;
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}
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return 0;
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}
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int _zero_timeout(const int semId, const struct timespec *timeout) {
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struct sembuf sops;
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sops.sem_num = 0;
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sops.sem_op = 0;
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sops.sem_flg = 0;
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while (semtimedop(semId, &sops, 1, timeout) == -1)
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if (errno != EINTR) {
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// err_msg(errno, "_zero_timeout");
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return errno;
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}
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return 0;
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}
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/* Release semaphore - increment it by 1 */
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int _inc(int semId) {
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struct sembuf sops;
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sops.sem_num = 0;
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sops.sem_op = 1;
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sops.sem_flg = 0;
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int rv = semop(semId, &sops, 1);
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if (rv == -1) {
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// err_msg(errno, "_inc");
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return errno;
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}
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return 0;
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}
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void _remove(int semid) {
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union semun dummy;
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if (semctl(semid, 0, IPC_RMID, dummy) == -1)
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err_msg(errno, "_remove");
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}
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int _set(int semId, int val) {
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union semun arg;
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arg.val = val;
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if (semctl(semId, 0, SETVAL, arg) == -1) {
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err_msg(errno, "_set");
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return errno;
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}
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return 0;
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}
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#define KEY 0x383
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int main() {
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int semid = _get(KEY, 1) ;
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if(_dec(semid) != 0)
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err_exit(errno, "_dec");
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printf("(%ld) 进入互斥区\n", (long) getpid());
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sleep(10);
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if(_inc(semid) != 0)
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err_exit(errno, "_inc");
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}
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