/*
 * (c) The GRASP/AQUA Project, Glasgow University, 1994-2004
 *
 * $Id: lockFile.c,v 1.5 2005/01/28 13:36:32 simonmar Exp $
 *
 * stdin/stout/stderr Runtime Support
 */

#if !(defined(_MSC_VER) || defined(__MINGW32__) || defined(_WIN32))

#include "HsBase.h"
#include "Rts.h"
#include "RtsUtils.h"

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;

    if (fd > FD_SETSIZE) {
	barf("lockFile: fd out of range");
    }

    while (fstat(fd, &sb) < 0) {
	if (errno != EINTR)
	    return -1;
    }

    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)
	    return -1;
      }
      /* 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) {
	     return -1;
	  }
        }
      }
      /* 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)
	     return -1;
      }
      /* 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;
}

#endif