1 /* Waiting for a subprocess to finish.
2 Copyright (C) 2001-2003, 2005-2021 Free Software Foundation, Inc.
3 Written by Bruno Haible <haible@clisp.cons.org>, 2001.
4
5 This program is free software: you can redistribute it and/or modify
6 it under the terms of the GNU General Public License as published by
7 the Free Software Foundation; either version 3 of the License, or
8 (at your option) any later version.
9
10 This program is distributed in the hope that it will be useful,
11 but WITHOUT ANY WARRANTY; without even the implied warranty of
12 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
13 GNU General Public License for more details.
14
15 You should have received a copy of the GNU General Public License
16 along with this program. If not, see <https://www.gnu.org/licenses/>. */
17
18
19 #include <config.h>
20
21 /* Specification. */
22 #include "wait-process.h"
23
24 #include <errno.h>
25 #include <stdlib.h>
26 #include <string.h>
27 #include <signal.h>
28
29 #include <sys/types.h>
30 #include <sys/wait.h>
31
32 #include "error.h"
33 #include "fatal-signal.h"
34 #include "xalloc.h"
35 #include "gettext.h"
36
37 #define _(str) gettext (str)
38
39 #define SIZEOF(a) (sizeof(a) / sizeof(a[0]))
40
41
42 #if defined _WIN32 && ! defined __CYGWIN__
43
44 # define WIN32_LEAN_AND_MEAN
45 # include <windows.h>
46
47 /* The return value of _spawnvp() is really a process handle as returned
48 by CreateProcess(). Therefore we can kill it using TerminateProcess. */
49 # define kill(pid,sig) TerminateProcess ((HANDLE) (pid), sig)
50
51 #endif
52
53
54 /* Type of an entry in the slaves array.
55 The 'used' bit determines whether this entry is currently in use.
56 (If pid_t was an atomic type like sig_atomic_t, we could just set the
57 'child' field to 0 when unregistering a slave process, and wouldn't need
58 the 'used' field.)
59 The 'used' and 'child' fields are accessed from within the cleanup_slaves()
60 action, therefore we mark them as 'volatile'. */
61 typedef struct
62 {
63 volatile sig_atomic_t used;
64 volatile pid_t child;
65 }
66 slaves_entry_t;
67
68 /* The registered slave subprocesses. */
69 static slaves_entry_t static_slaves[32];
70 static slaves_entry_t * volatile slaves = static_slaves;
71 static sig_atomic_t volatile slaves_count = 0;
72 static size_t slaves_allocated = SIZEOF (static_slaves);
73
74 /* The termination signal for slave subprocesses.
75 2003-10-07: Terminator becomes Governator. */
76 #ifdef SIGHUP
77 # define TERMINATOR SIGHUP
78 #else
79 # define TERMINATOR SIGTERM
80 #endif
81
82 /* The cleanup action. It gets called asynchronously. */
83 static _GL_ASYNC_SAFE void
84 cleanup_slaves (void)
85 {
86 for (;;)
87 {
88 /* Get the last registered slave. */
89 size_t n = slaves_count;
90 if (n == 0)
91 break;
92 n--;
93 slaves_count = n;
94 /* Skip unused entries in the slaves array. */
95 if (slaves[n].used)
96 {
97 pid_t slave = slaves[n].child;
98
99 /* Kill the slave. */
100 kill (slave, TERMINATOR);
101 }
102 }
103 }
104
105 /* The cleanup action, taking a signal argument.
106 It gets called asynchronously. */
107 static _GL_ASYNC_SAFE void
108 cleanup_slaves_action (_GL_UNUSED int sig)
109 {
110 cleanup_slaves ();
111 }
112
113 /* Register a subprocess as being a slave process. This means that the
114 subprocess will be terminated when its creator receives a catchable fatal
115 signal or exits normally. Registration ends when wait_subprocess()
116 notices that the subprocess has exited. */
117 void
118 register_slave_subprocess (pid_t child)
119 {
120 static bool cleanup_slaves_registered = false;
121 if (!cleanup_slaves_registered)
122 {
123 atexit (cleanup_slaves);
124 if (at_fatal_signal (cleanup_slaves_action) < 0)
125 xalloc_die ();
126 cleanup_slaves_registered = true;
127 }
128
129 /* Try to store the new slave in an unused entry of the slaves array. */
130 {
131 slaves_entry_t *s = slaves;
132 slaves_entry_t *s_end = s + slaves_count;
133
134 for (; s < s_end; s++)
135 if (!s->used)
136 {
137 /* The two uses of 'volatile' in the slaves_entry_t type above
138 (and ISO C 99 section 5.1.2.3.(5)) ensure that we mark the
139 entry as used only after the child pid has been written to the
140 memory location s->child. */
141 s->child = child;
142 s->used = 1;
143 return;
144 }
145 }
146
147 if (slaves_count == slaves_allocated)
148 {
149 /* Extend the slaves array. Note that we cannot use xrealloc(),
150 because then the cleanup_slaves() function could access an already
151 deallocated array. */
152 slaves_entry_t *old_slaves = slaves;
153 size_t new_slaves_allocated = 2 * slaves_allocated;
154 slaves_entry_t *new_slaves =
155 (slaves_entry_t *)
156 malloc (new_slaves_allocated * sizeof (slaves_entry_t));
157 if (new_slaves == NULL)
158 {
159 /* xalloc_die() will call exit() which will invoke cleanup_slaves().
160 Additionally we need to kill child, because it's not yet among
161 the slaves list. */
162 kill (child, TERMINATOR);
163 xalloc_die ();
164 }
165 memcpy (new_slaves, old_slaves,
166 slaves_allocated * sizeof (slaves_entry_t));
167 slaves = new_slaves;
168 slaves_allocated = new_slaves_allocated;
169 /* Now we can free the old slaves array. */
170 if (old_slaves != static_slaves)
171 free (old_slaves);
172 }
173 /* The three uses of 'volatile' in the types above (and ISO C 99 section
174 5.1.2.3.(5)) ensure that we increment the slaves_count only after the
175 new slave and its 'used' bit have been written to the memory locations
176 that make up slaves[slaves_count]. */
177 slaves[slaves_count].child = child;
178 slaves[slaves_count].used = 1;
179 slaves_count++;
180 }
181
182 /* Unregister a child from the list of slave subprocesses. */
183 static void
184 unregister_slave_subprocess (pid_t child)
185 {
186 /* The easiest way to remove an entry from a list that can be used by
187 an asynchronous signal handler is just to mark it as unused. For this,
188 we rely on sig_atomic_t. */
189 slaves_entry_t *s = slaves;
190 slaves_entry_t *s_end = s + slaves_count;
191
192 for (; s < s_end; s++)
193 if (s->used && s->child == child)
194 s->used = 0;
195 }
196
197
198 /* Wait for a subprocess to finish. Return its exit code.
199 If it didn't terminate correctly, exit if exit_on_error is true, otherwise
200 return 127. */
201 int
202 wait_subprocess (pid_t child, const char *progname,
203 bool ignore_sigpipe, bool null_stderr,
204 bool slave_process, bool exit_on_error,
205 int *termsigp)
206 {
207 #if HAVE_WAITID && defined WNOWAIT && 0
208 /* Commented out because waitid() without WEXITED and with WNOWAIT doesn't
209 work: On Solaris 7 and OSF/1 4.0, it returns -1 and sets errno = ECHILD,
210 and on HP-UX 10.20 it just hangs. */
211 /* Use of waitid() with WNOWAIT avoids a race condition: If slave_process is
212 true, and this process sleeps a very long time between the return from
213 waitpid() and the execution of unregister_slave_subprocess(), and
214 meanwhile another process acquires the same PID as child, and then - still
215 before unregister_slave_subprocess() - this process gets a fatal signal,
216 it would kill the other totally unrelated process. */
217 siginfo_t info;
218
219 if (termsigp != NULL)
220 *termsigp = 0;
221 for (;;)
222 {
223 if (waitid (P_PID, child, &info, WEXITED | (slave_process ? WNOWAIT : 0))
224 < 0)
225 {
226 # ifdef EINTR
227 if (errno == EINTR)
228 continue;
229 # endif
230 if (exit_on_error || !null_stderr)
231 error (exit_on_error ? EXIT_FAILURE : 0, errno,
232 _("%s subprocess"), progname);
233 return 127;
234 }
235
236 /* info.si_code is set to one of CLD_EXITED, CLD_KILLED, CLD_DUMPED,
237 CLD_TRAPPED, CLD_STOPPED, CLD_CONTINUED. Loop until the program
238 terminates. */
239 if (info.si_code == CLD_EXITED
240 || info.si_code == CLD_KILLED || info.si_code == CLD_DUMPED)
241 break;
242 }
243
244 /* The child process has exited or was signalled. */
245
246 if (slave_process)
247 {
248 /* Unregister the child from the list of slave subprocesses, so that
249 later, when we exit, we don't kill a totally unrelated process which
250 may have acquired the same pid. */
251 unregister_slave_subprocess (child);
252
253 /* Now remove the zombie from the process list. */
254 for (;;)
255 {
256 if (waitid (P_PID, child, &info, WEXITED) < 0)
257 {
258 # ifdef EINTR
259 if (errno == EINTR)
260 continue;
261 # endif
262 if (exit_on_error || !null_stderr)
263 error (exit_on_error ? EXIT_FAILURE : 0, errno,
264 _("%s subprocess"), progname);
265 return 127;
266 }
267 break;
268 }
269 }
270
271 switch (info.si_code)
272 {
273 case CLD_KILLED:
274 case CLD_DUMPED:
275 if (termsigp != NULL)
276 *termsigp = info.si_status; /* TODO: or info.si_signo? */
277 # ifdef SIGPIPE
278 if (info.si_status == SIGPIPE && ignore_sigpipe)
279 return 0;
280 # endif
281 if (exit_on_error || (!null_stderr && termsigp == NULL))
282 error (exit_on_error ? EXIT_FAILURE : 0, 0,
283 _("%s subprocess got fatal signal %d"),
284 progname, info.si_status);
285 return 127;
286 case CLD_EXITED:
287 if (info.si_status == 127)
288 {
289 if (exit_on_error || !null_stderr)
290 error (exit_on_error ? EXIT_FAILURE : 0, 0,
291 _("%s subprocess failed"), progname);
292 return 127;
293 }
294 return info.si_status;
295 default:
296 abort ();
297 }
298 #else
299 /* waitpid() is just as portable as wait() nowadays. */
300 int status;
301
302 if (termsigp != NULL)
303 *termsigp = 0;
304 status = 0;
305 for (;;)
306 {
307 int result = waitpid (child, &status, 0);
308
309 if (result != child)
310 {
311 # ifdef EINTR
312 if (errno == EINTR)
313 continue;
314 # endif
315 # if 0 /* defined ECHILD */
316 if (errno == ECHILD)
317 {
318 /* Child process nonexistent?! Assume it terminated
319 successfully. */
320 status = 0;
321 break;
322 }
323 # endif
324 if (exit_on_error || !null_stderr)
325 error (exit_on_error ? EXIT_FAILURE : 0, errno,
326 _("%s subprocess"), progname);
327 return 127;
328 }
329
330 /* One of WIFSIGNALED (status), WIFEXITED (status), WIFSTOPPED (status)
331 must always be true, since we did not specify WCONTINUED in the
332 waitpid() call. Loop until the program terminates. */
333 if (!WIFSTOPPED (status))
334 break;
335 }
336
337 /* The child process has exited or was signalled. */
338
339 if (slave_process)
340 /* Unregister the child from the list of slave subprocesses, so that
341 later, when we exit, we don't kill a totally unrelated process which
342 may have acquired the same pid. */
343 unregister_slave_subprocess (child);
344
345 if (WIFSIGNALED (status))
346 {
347 if (termsigp != NULL)
348 *termsigp = WTERMSIG (status);
349 # ifdef SIGPIPE
350 if (WTERMSIG (status) == SIGPIPE && ignore_sigpipe)
351 return 0;
352 # endif
353 if (exit_on_error || (!null_stderr && termsigp == NULL))
354 error (exit_on_error ? EXIT_FAILURE : 0, 0,
355 _("%s subprocess got fatal signal %d"),
356 progname, (int) WTERMSIG (status));
357 return 127;
358 }
359 if (!WIFEXITED (status))
360 abort ();
361 if (WEXITSTATUS (status) == 127)
362 {
363 if (exit_on_error || !null_stderr)
364 error (exit_on_error ? EXIT_FAILURE : 0, 0,
365 _("%s subprocess failed"), progname);
366 return 127;
367 }
368 return WEXITSTATUS (status);
369 #endif
370 }