#include <lib.h>

#include <errno.h>

#include <sys/types.h>

#include <unistd.h>

#include <string.h>

#include <fcntl.h>

#include <stdio.h>

#if _ANSI

#include <stdlib.h>

#endif

typedef enum {

False, True

} BOOLEAN;

#define LOCKDIR "/tmp/" /* or /usr/tmp/ as the case may be */

#define MAXTRIES 3

#define NAPTIME (unsigned int)5

PRIVATE _PROTOTYPE( char *lockpath, (char *name));

_PROTOTYPE( void syserr, (char *errstring));

_PROTOTYPE( BOOLEAN lock, (char *name));

_PROTOTYPE( void unlock, (char *name));

void

syserr(errstring)

char *errstring;

{

fprintf(stderr,"couldn't %s\n", errstring);

exit(1);

}

BOOLEAN lock(name) /* acquire lock */

char *name;

{

char *path;

int fd, tries;

path = lockpath(name);

tries = 0;

while ((fd = creat(path, 0)) == -1 && errno == EACCES) {

if (++tries >= MAXTRIES) return(False);

sleep(NAPTIME);

}

if (fd == -1 || close(fd) == -1) syserr("lock");

return(True);

}

void unlock(name) /* free lock */

char *name;

{

if (unlink(lockpath(name)) == -1) syserr("unlock");

}

PRIVATE char *lockpath(name) /* generate lock file path */

char *name;

{

PRIVATE char path[20];

strcpy(path, LOCKDIR);

return(strcat(path, name));

}