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Annotation of 40BSD/cmd/ucbmail/lock.c, revision 1.1

1.1     ! root        1: #
        !             2: 
        !             3: /*
        !             4:  * A mailing program.
        !             5:  *
        !             6:  * Stuff to do version 7 style locking.
        !             7:  */
        !             8: 
        !             9: #include "rcv.h"
        !            10: #include <sys/stat.h>
        !            11: 
        !            12: char   *maillock       = ".lock";              /* Lock suffix for mailname */
        !            13: char   *lockname       = "/usr/spool/mail/tmXXXXXX";
        !            14: char   locktmp[30];                            /* Usable lock temporary */
        !            15: static char            curlock[50];            /* Last used name of lock */
        !            16: static int             locked;                 /* To note that we locked it */
        !            17: 
        !            18: /*
        !            19:  * Lock the specified mail file by setting the file mailfile.lock.
        !            20:  * We must, of course, be careful to remove the lock file by a call
        !            21:  * to unlock before we stop.  The algorithm used here is to see if
        !            22:  * the lock exists, and if it does, to check its modify time.  If it
        !            23:  * is older than 30 seconds, we assume error and set our own file.
        !            24:  * Otherwise, we wait for 5 seconds and try again.
        !            25:  */
        !            26: 
        !            27: lock(file)
        !            28: char *file;
        !            29: {
        !            30:        register int f;
        !            31:        struct stat sbuf;
        !            32:        long curtime;
        !            33: 
        !            34:        if (file == NOSTR) {
        !            35:                printf("Locked = %d\n", locked);
        !            36:                return(0);
        !            37:        }
        !            38:        if (locked)
        !            39:                return(0);
        !            40:        strcpy(curlock, file);
        !            41:        strcat(curlock, maillock);
        !            42:        strcpy(locktmp, lockname);
        !            43:        mktemp(locktmp);
        !            44:        remove(locktmp);
        !            45:        for (;;) {
        !            46:                f = lock1(locktmp, curlock);
        !            47:                if (f == 0) {
        !            48:                        locked = 1;
        !            49:                        return(0);
        !            50:                }
        !            51:                if (stat(curlock, &sbuf) < 0)
        !            52:                        return(0);
        !            53:                time(&curtime);
        !            54:                if (curtime < sbuf.st_ctime + 30) {
        !            55:                        sleep(5);
        !            56:                        continue;
        !            57:                }
        !            58:                remove(curlock);
        !            59:        }
        !            60: }
        !            61: 
        !            62: /*
        !            63:  * Remove the mail lock, and note that we no longer
        !            64:  * have it locked.
        !            65:  */
        !            66: 
        !            67: unlock()
        !            68: {
        !            69: 
        !            70:        remove(curlock);
        !            71:        locked = 0;
        !            72: }
        !            73: 
        !            74: /*
        !            75:  * Attempt to set the lock by creating the temporary file,
        !            76:  * then doing a link/unlink.  If it fails, return -1 else 0
        !            77:  */
        !            78: 
        !            79: lock1(tempfile, name)
        !            80:        char tempfile[], name[];
        !            81: {
        !            82:        register int fd;
        !            83: 
        !            84:        fd = creat(tempfile, 0);
        !            85:        if (fd < 0)
        !            86:                return(-1);
        !            87:        close(fd);
        !            88:        if (link(tempfile, name) < 0) {
        !            89:                remove(tempfile);
        !            90:                return(-1);
        !            91:        }
        !            92:        remove(tempfile);
        !            93:        return(0);
        !            94: }

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