flock user defined function

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);
}