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/*
* (c) The GRASP/AQUA Project, Glasgow University, 1994-1998
*
* $Id: lockFile.c,v 1.2 2001/05/21 11:02:15 simonmar Exp $
*
* stdin/stout/stderr Runtime Support
*/
#include "HsStd.h"
#ifndef FD_SETSIZE
#define FD_SETSIZE 256
#endif
typedef struct {
dev_t device;
ino_t inode;
int fd;
} Lock;
static Lock readLock[FD_SETSIZE];
static Lock writeLock[FD_SETSIZE];
static int readLocks = 0;
static int writeLocks = 0;
int
lockFile(int fd, int for_writing, int exclusive)
{
struct stat sb;
int i;
while (fstat(fd, &sb) < 0) {
if (errno != EINTR) {
#ifndef _WIN32
return -1;
#else
/* fstat()ing socket fd's seems to fail with CRT's fstat(),
so let's just silently return and hope for the best..
*/
return 0;
#endif
}
}
if (for_writing) {
/* opening a file for writing, check to see whether
we don't have any read locks on it already.. */
for (i = 0; i < readLocks; i++) {
if (readLock[i].inode == sb.st_ino && readLock[i].device == sb.st_dev) {
#ifndef __MINGW32__
return -1;
#else
break;
#endif
}
}
/* If we're determined that there is only a single
writer to the file, check to see whether the file
hasn't already been opened for writing..
*/
if (exclusive) {
for (i = 0; i < writeLocks; i++) {
if (writeLock[i].inode == sb.st_ino && writeLock[i].device == sb.st_dev) {
#ifndef __MINGW32__
return -1;
#else
break;
#endif
}
}
}
/* OK, everything is cool lock-wise, record it and leave. */
i = writeLocks++;
writeLock[i].device = sb.st_dev;
writeLock[i].inode = sb.st_ino;
writeLock[i].fd = fd;
return 0;
} else {
/* For reading, it's simpler - just check to see
that there's no-one writing to the underlying file. */
for (i = 0; i < writeLocks; i++) {
if (writeLock[i].inode == sb.st_ino && writeLock[i].device == sb.st_dev) {
#ifndef __MINGW32__
return -1;
#else
break;
#endif
}
}
/* Fit in new entry, reusing an existing table entry, if possible. */
for (i = 0; i < readLocks; i++) {
if (readLock[i].inode == sb.st_ino && readLock[i].device == sb.st_dev) {
return 0;
}
}
i = readLocks++;
readLock[i].device = sb.st_dev;
readLock[i].inode = sb.st_ino;
readLock[i].fd = fd;
return 0;
}
}
int
unlockFile(int fd)
{
int i;
for (i = 0; i < readLocks; i++)
if (readLock[i].fd == fd) {
while (++i < readLocks)
readLock[i - 1] = readLock[i];
readLocks--;
return 0;
}
for (i = 0; i < writeLocks; i++)
if (writeLock[i].fd == fd) {
while (++i < writeLocks)
writeLock[i - 1] = writeLock[i];
writeLocks--;
return 0;
}
/* Signal that we did not find an entry */
return 1;
}
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