[GENERAL] flock user defined function

[Chris Goughnour]

I'm trying to write two C language user defined functions, lockfile() and
unlockfile(), that call flock using LOCK_EX and LOCK_UN respectively.  If I
call lockfile from a first psql process it returns successfully.  Calling
lockfile from a second psql process blocks. However, when I call unlockfile
from the first psql process, the second process still blocks.  The lockfile
call from the second psql proccess doesn't return until I kill the first
psql process.
Any suggestions? Thanks in advance.
Chris Goughnour

PG_FUNCTION_INFO_V1(lockFile);
Datum lockFile(PG_FUNCTION_ARGS){
        text *t=PG_GETARG_TEXT_P(0);
        char *path=palloc(VARSIZE(t)-VARHDRSZ+1);
        int fileHandle,status;
        memcpy((void *)path,(void *)VARDATA(t),VARSIZE(t)-VARHDRSZ);
        path[VARSIZE(t)-VARHDRSZ]=0;
        fileHandle=open((const char *)path,O_RDONLY);
        if(fileHandle==-1){
                PG_RETURN_INT32(-1);
        }
        if(flock(fileHandle,LOCK_EX)==-1){
                PG_RETURN_INT32(-1);
        }
        PG_RETURN_INT32(0);
}

PG_FUNCTION_INFO_V1(unlockFile);
Datum unlockFile(PG_FUNCTION_ARGS){
        text *t=PG_GETARG_TEXT_P(0);
        char *path=palloc(VARSIZE(t)-VARHDRSZ+1);
        int fileHandle;
        memcpy((void *)path,(void *)VARDATA(t),VARSIZE(t)-VARHDRSZ);
        path[VARSIZE(t)-VARHDRSZ]=0;
        fileHandle=open((const char *)path,O_RDONLY);
        if(fileHandle==-1){
                PG_RETURN_INT32(-1);
        }
        if(flock(fileHandle,LOCK_UN)==-1){
                PG_RETURN_INT32(-1);
        }
        PG_RETURN_INT32(0);
}


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