cbits/lockFile.c

   1 /*
   2  * (c) The GRASP/AQUA Project, Glasgow University, 1994-2004
   3  *
   4  * $Id: lockFile.c,v 1.5 2005/01/28 13:36:32 simonmar Exp $
   5  *
   6  * stdin/stout/stderr Runtime Support
   7  */
   8
   9 #if !(defined(_MSC_VER) || defined(__MINGW32__) || defined(_WIN32))
  10
  11 #include "HsBase.h"
  12 #include "Rts.h"
  13 #include "RtsUtils.h"
  14
  15 typedef struct {
  16     dev_t device;
  17     ino_t inode;
  18     int fd;
  19 } Lock;
  20
  21 static Lock readLock[FD_SETSIZE];
  22 static Lock writeLock[FD_SETSIZE];
  23
  24 static int readLocks = 0;
  25 static int writeLocks = 0;
  26
  27 int
  28 lockFile(int fd, int for_writing, int exclusive)
  29 {
  30     struct stat sb;
  31     int i;
  32
  33     if (fd > FD_SETSIZE) {
  34         barf("lockFile: fd out of range");
  35     }
  36
  37     while (fstat(fd, &sb) < 0) {
  38         if (errno != EINTR)
  39             return -1;
  40     }
  41
  42     if (for_writing) {
  43       /* opening a file for writing, check to see whether
  44          we don't have any read locks on it already.. */
  45       for (i = 0; i < readLocks; i++) {
  46          if (readLock[i].inode == sb.st_ino && readLock[i].device == sb.st_dev)
  47             return -1;
  48       }
  49       /* If we're determined that there is only a single
  50          writer to the file, check to see whether the file
  51          hasn't already been opened for writing..
  52       */
  53       if (exclusive) {
  54         for (i = 0; i < writeLocks; i++) {
  55           if (writeLock[i].inode == sb.st_ino && writeLock[i].device == sb.st_dev) {
  56              return -1;
  57           }
  58         }
  59       }
  60       /* OK, everything is cool lock-wise, record it and leave. */
  61       i = writeLocks++;
  62       writeLock[i].device = sb.st_dev;
  63       writeLock[i].inode = sb.st_ino;
  64       writeLock[i].fd = fd;
  65       return 0;
  66     } else {
  67       /* For reading, it's simpler - just check to see
  68          that there's no-one writing to the underlying file. */
  69       for (i = 0; i < writeLocks; i++) {
  70         if (writeLock[i].inode == sb.st_ino && writeLock[i].device == sb.st_dev)
  71              return -1;
  72       }
  73       /* Fit in new entry, reusing an existing table entry, if possible. */
  74       for (i = 0; i < readLocks; i++) {
  75          if (readLock[i].inode == sb.st_ino && readLock[i].device == sb.st_dev) {
  76            return 0;
  77          }
  78       }
  79       i = readLocks++;
  80       readLock[i].device = sb.st_dev;
  81       readLock[i].inode = sb.st_ino;
  82       readLock[i].fd = fd;
  83       return 0;
  84     }
  85
  86 }
  87
  88 int
  89 unlockFile(int fd)
  90 {
  91     int i;
  92
  93     for (i = 0; i < readLocks; i++)
  94         if (readLock[i].fd == fd) {
  95             while (++i < readLocks)
  96                 readLock[i - 1] = readLock[i];
  97             readLocks--;
  98             return 0;
  99         }
 100
 101     for (i = 0; i < writeLocks; i++)
 102         if (writeLock[i].fd == fd) {
 103             while (++i < writeLocks)
 104                 writeLock[i - 1] = writeLock[i];
 105             writeLocks--;
 106             return 0;
 107         }
 108      /* Signal that we did not find an entry */
 109     return 1;
 110 }
 111
 112 #endif