GRASS GIS 7 Programmer's Manual  7.5.svn(2018)-r72741
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lock.c
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1 #include <stdlib.h>
2 #include <stdio.h>
3 #include <string.h>
4 #include <fcntl.h>
5 #include <unistd.h>
6 #include <sys/types.h>
7 #include <sys/stat.h>
8 #include <signal.h>
9 #include "local_proto.h"
10 #include <grass/gis.h>
11 #include <grass/glocale.h>
12 
13 /******************************************************************
14 *lock file pid
15 *
16 * this programs "locks" the file for process pid:
17 *
18 * 1. if file exists, the pid is read out of the file. if this
19 * process is still running, the file is considered locked.
20 * exit(2).
21 * 2. something weird happened. G_fatal_error() aka exit(1)
22 * 3. if file does not exist, or if file exists but process is not
23 * running (ie, lock was not removed), the file is locked for
24 * process pid by writing pid into the file.
25 * exit(0).
26 ******************************************************************/
27 
28 #include <errno.h>
29 
30 int main(int argc, char *argv[])
31 {
32  int pid;
33  int lockpid;
34  int lock;
35  int locked;
36 
37  if (argc != 3 || sscanf(argv[2], "%d", &lockpid) != 1)
38  G_fatal_error(_("Usage: %s file pid"), argv[0]);
39 #define file argv[1]
40 
41 #ifdef __MINGW32__
42  G_warning(_("Concurrent mapset locking is not supported on Windows"));
43  exit(0);
44 #else
45  locked = 0;
46  if ((lock = open(file, 0)) >= 0) { /* file exists */
47  G_sleep(1); /* allow time for file creator to write its pid */
48  if (read(lock, &pid, sizeof pid) == sizeof pid)
49  locked = find_process(pid);
50  close(lock);
51  }
52  if (locked)
53  exit(2);
54 
55  if ((lock = creat(file, 0666)) < 0) {
56  perror(file);
57  G_fatal_error("%s: ", argv[0]);
58  }
59  if (write(lock, &lockpid, sizeof lockpid) != sizeof lockpid)
60  G_fatal_error(_("Unable to write lockfile %s (%s)"),
61  file, strerror(errno));
62  close(lock);
63  exit(0);
64 #endif
65 }
66 
67 int find_process(int pid)
68 {
69  /* attempt to kill pid with NULL signal. if success, then
70  process pid is still running. otherwise, must check if
71  kill failed because no such process, or because user is
72  not owner of process
73  */
74 #ifdef __MINGW32__
75  return 0;
76 #else
77  if (kill(pid, 0) == 0)
78  return 1;
79  return errno != ESRCH;
80 #endif
81 }
int main(int argc, char *argv[])
Definition: main.c:27
void G_fatal_error(const char *msg,...)
Print a fatal error message to stderr.
Definition: gis/error.c:160
int find_process(int pid)
Definition: clean_temp.c:171
void G_sleep(unsigned int seconds)
Definition: sleep.c:11
#define file
#define _(str)
Definition: glocale.h:13
close(fd)
void G_warning(const char *msg,...)
Print a warning message to stderr.
Definition: gis/error.c:204