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