base/libs/qdecoder/qSem.c

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/*
 * Copyright 2008 The qDecoder Project. All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE QDECODER PROJECT ``AS IS'' AND ANY
 * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
 * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
 * DISCLAIMED. IN NO EVENT SHALL THE QDECODER PROJECT BE LIABLE FOR ANY
 * DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
 * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
 * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
 * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

#ifndef DISABLE_IPC

#include <stdio.h>
#include <stdlib.h>
#include <stdbool.h>
#include <unistd.h>
#include <sys/sem.h>
#include "qDecoder.h"
#include "qInternal.h"

int qSemInit(const char *keyfile, int keyid, int nsems, bool ifexistdestroy) {
    key_t semkey;
    int semid;

    // generate unique key using ftok();
    if(keyfile != NULL) {
        semkey = ftok(keyfile, keyid);
        if (semkey == -1) return -1;
    } else {
        semkey = IPC_PRIVATE;
    }

    // create semaphores
    if ((semid = semget(semkey, nsems, IPC_CREAT | IPC_EXCL | 0666)) == -1) {
        if(ifexistdestroy == false) return -1;

        // destroy & re-create
        if((semid = qSemGetId(keyfile, keyid)) >= 0) qSemFree(semid);
        if ((semid = semget(semkey, nsems, IPC_CREAT | IPC_EXCL | 0666)) == -1) return -1;
    }

    // initializing
    int i;
    for (i = 0; i < nsems; i++) {
        struct sembuf sbuf;

        /* set sbuf */
        sbuf.sem_num = i;
        sbuf.sem_op = 1;
        sbuf.sem_flg = 0;

        /* initialize */
        if (semop(semid, &sbuf, 1) != 0) {
            qSemFree(semid);
            return -1;
        }
    }

    return semid;
}


int qSemGetId(const char *keyfile, int keyid) {
    int semid;

    /* generate unique key using ftok() */
    key_t semkey = ftok(keyfile, keyid);
    if (semkey == -1) return -1;

    /* get current semaphore id */
    if ((semid = semget(semkey, 0, 0)) == -1) return -1;

    return semid;
}

bool qSemEnter(int semid, int semno) {
    struct sembuf sbuf;

    /* set sbuf */
    sbuf.sem_num = semno;
    sbuf.sem_op = -1;
    sbuf.sem_flg = SEM_UNDO;

    /* lock */
    if (semop(semid, &sbuf, 1) != 0) return false;
    return true;
}

bool qSemEnterNowait(int semid, int semno) {
    struct sembuf sbuf;

    /* set sbuf */
    sbuf.sem_num = semno;
    sbuf.sem_op = -1;
    sbuf.sem_flg = SEM_UNDO | IPC_NOWAIT;

    /* lock */
    if (semop(semid, &sbuf, 1) != 0) return false;
    return true;
}

bool qSemEnterForce(int semid, int semno, int maxwaitms, bool *forceflag) {
    int wait;
    for(wait = 0; wait < maxwaitms; wait += 10) {
        if(qSemEnterNowait(semid, semno) == true) {
            if(forceflag != NULL) *forceflag = false;
            return true;
        }
        usleep(10*1000); // sleep 10ms
    }

    DEBUG("force to unlock semaphore %d-%d", semid, semno);
    while(true) {
        qSemLeave(semid, semno);
        if(qSemEnterNowait(semid, semno) == true) break;
    }

    if(forceflag != NULL) *forceflag = true;
    return true;
}

bool qSemLeave(int semid, int semno) {
    struct sembuf sbuf;

    /* set sbuf */
    sbuf.sem_num = semno;
    sbuf.sem_op = 1;
    sbuf.sem_flg = SEM_UNDO;

    /* unlock */
    if (semop(semid, &sbuf, 1) != 0) return false;
    return true;
}

bool qSemCheck(int semid, int semno) {
    if(semctl(semid, semno, GETVAL, 0) == 0) return true; // locked
    return false; // unlocked
}

bool qSemFree(int semid) {
    if (semid < 0) return false;
    if (semctl(semid, 0, IPC_RMID, 0) != 0) return false;
    return true;
}

#endif /* DISABLE_IPC */

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