archie/tcl-dp/unix/dpLocks.c
2024-05-27 16:13:40 +02:00

100 lines
2.4 KiB
C
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#include <stdio.h>
#include <errno.h>
/*
* If the lock is set by another process, PutLock will make an attempt to remove
* it every SLEEP_TIME seconds.
*/
#define SLEEP_TIME 1
#define ERROR(x) { \
FILE *fp; \
char buffer [1000]; \
sprintf(buffer, "%s place %d error = %d", SOURCE, x, errno);\
perror(buffer); \
fp = fopen("ERROR", "a"); \
fprintf(fp, buffer); \
fclose(fp); \
};
/*
* PutLock --
*
* Creates a symbolic link on the file given in lockFilePath. The name of
* the file the link points is a string representing the process number of
* the filter process. If the link already exists, the program checks if
* the process whose number is given in the symbolic link still exists. If
* yes, the program waits for one second and then checks again for the
* status of the lock. If no, the existing lock is removed and the new one
* is put in its place.
*
* Results:
*
* The return value is 2 if the operation failed, otherwise it is 0.
*
* Side effects:
*
* Puts a lock (symbolic link) on the given file.
*
*/
int
PutLock (lockFilePath)
char *lockFilePath; /* File to put lock on. */
{
char pid [15];
sprintf(pid, "%ld", (long)getpid());
/*
* Waiting for lock to be removed or for timeout.
* If other error than "already existing link" occurs, exit.
*/
while(symlink(pid, lockFilePath) == -1) {
sleep(1);
}
return 0;
}
/*
* RemoveLock --
*
* Remove the symbolic link from the file given in lockFilePath. The link
* is removed only if it was put by this process (this is checked by
* comparing the value of the symbolink link with the ptrocess id).
*
* Results:
*
* The return value is 2 if the operation failed, otherwise it is 0.
*
* Side effects:
*
* None.
*/
int
RemoveLock (lockFilePath)
char *lockFilePath; /* File to remove lock from. */
{
if(unlink(lockFilePath) != 0) {
FILE *fp = fopen("/usr/u/mperham/FILTER", "a");
ERROR(8);
return 2;
}
return 0;
}