version 4, including all changes.
.
Rev |
Author |
# |
Line |
1 |
perry |
1 |
WAIT |
|
|
2 |
!!!WAIT |
|
|
3 |
NAME |
|
|
4 |
SYNOPSIS |
|
|
5 |
DESCRIPTION |
|
|
6 |
RETURN VALUE |
|
|
7 |
ERRORS |
|
|
8 |
NOTES |
|
|
9 |
CONFORMING TO |
|
|
10 |
SEE ALSO |
|
|
11 |
---- |
|
|
12 |
!!NAME |
|
|
13 |
|
|
|
14 |
|
|
|
15 |
wait, waitpid - wait for process termination |
|
|
16 |
!!SYNOPSIS |
|
|
17 |
|
|
|
18 |
|
|
|
19 |
__#include __ |
|
|
20 |
#include __ |
|
|
21 |
|
|
|
22 |
|
|
|
23 |
__pid_t wait(int *__''status''__) |
|
|
24 |
pid_t waitpid(pid_t__ ''pid''__, int |
|
|
25 |
*__''status''__, int__ |
|
|
26 |
''options''__);__ |
|
|
27 |
!!DESCRIPTION |
|
|
28 |
|
|
|
29 |
|
|
|
30 |
The __wait__ function suspends execution of the current |
|
|
31 |
process until a child has exited, or until a signal is |
|
|
32 |
delivered whose action is to terminate the current process |
|
|
33 |
or to call a signal handling function. If a child has |
|
|
34 |
already exited by the time of the call (a so-called |
|
|
35 |
__ |
|
|
36 |
|
|
|
37 |
|
|
|
38 |
The __waitpid__ function suspends execution of the |
|
|
39 |
current process until a child as specified by the ''pid'' |
|
|
40 |
argument has exited, or until a signal is delivered whose |
|
|
41 |
action is to terminate the current process or to call a |
|
|
42 |
signal handling function. If a child as requested by |
|
|
43 |
''pid'' has already exited by the time of the call (a |
|
|
44 |
so-called |
|
|
45 |
'' |
|
|
46 |
|
|
|
47 |
|
|
|
48 |
The value of ''pid'' can be one of: |
|
|
49 |
|
|
|
50 |
|
|
|
51 |
|
|
|
52 |
|
|
|
53 |
which means to wait for any child process whose process |
|
|
54 |
group ID is equal to the absolute value of |
|
|
55 |
''pid''. |
|
|
56 |
|
|
|
57 |
|
|
|
58 |
-1 |
|
|
59 |
|
|
|
60 |
|
|
|
61 |
which means to wait for any child process; this is the same |
|
|
62 |
behaviour which __wait__ exhibits. |
|
|
63 |
|
|
|
64 |
|
|
|
65 |
0 |
|
|
66 |
|
|
|
67 |
|
|
|
68 |
which means to wait for any child process whose process |
|
|
69 |
group ID is equal to that of the calling |
|
|
70 |
process. |
|
|
71 |
|
|
|
72 |
|
|
|
73 |
|
|
|
74 |
|
|
|
75 |
which means to wait for the child whose process ID is equal |
|
|
76 |
to the value of ''pid''. |
|
|
77 |
|
|
|
78 |
|
|
|
79 |
The value of ''options'' is an OR of zero or more of the |
|
|
80 |
following constants: |
|
|
81 |
|
|
|
82 |
|
|
|
83 |
__WNOHANG__ |
|
|
84 |
|
|
|
85 |
|
|
|
86 |
which means to return immediately if no child has |
|
|
87 |
exited. |
|
|
88 |
|
|
|
89 |
|
|
|
90 |
__WUNTRACED__ |
|
|
91 |
|
|
|
92 |
|
|
|
93 |
which means to also return for children which are stopped, |
|
|
94 |
and whose status has not been reported. |
|
|
95 |
|
|
|
96 |
|
|
|
97 |
If ''status'' is not __NULL__, __wait__ or |
|
|
98 |
__waitpid__ store status information in the location |
|
|
99 |
pointed to by ''status''. |
|
|
100 |
|
|
|
101 |
|
|
|
102 |
This status can be evaluated with the following macros |
|
|
103 |
(these macros take the stat buffer (an __int__) as an |
|
|
104 |
argument -- not a pointer to the buffer!): |
|
|
105 |
|
|
|
106 |
|
|
|
107 |
__WIFEXITED(__''status''__)__ |
|
|
108 |
|
|
|
109 |
|
|
|
110 |
is non-zero if the child exited normally. |
|
|
111 |
|
|
|
112 |
|
|
|
113 |
__WEXITSTATUS(__''status''__)__ |
|
|
114 |
|
|
|
115 |
|
|
|
116 |
evaluates to the least significant eight bits of the return |
|
|
117 |
code of the child which terminated, which may have been set |
|
|
118 |
as the argument to a call to __exit()__ or as the |
|
|
119 |
argument for a __return__ statement in the main program. |
|
|
120 |
This macro can only be evaluated if __WIFEXITED__ |
|
|
121 |
returned non-zero. |
|
|
122 |
|
|
|
123 |
|
|
|
124 |
__WIFSIGNALED(__''status''__)__ |
|
|
125 |
|
|
|
126 |
|
|
|
127 |
returns true if the child process exited because of a signal |
|
|
128 |
which was not caught. |
|
|
129 |
|
|
|
130 |
|
|
|
131 |
__WTERMSIG(__''status''__)__ |
|
|
132 |
|
|
|
133 |
|
|
|
134 |
returns the number of the signal that caused the child |
|
|
135 |
process to terminate. This macro can only be evaluated if |
|
|
136 |
__WIFSIGNALED__ returned non-zero. |
|
|
137 |
|
|
|
138 |
|
|
|
139 |
__WIFSTOPPED(__''status''__)__ |
|
|
140 |
|
|
|
141 |
|
|
|
142 |
returns true if the child process which caused the return is |
|
|
143 |
currently stopped; this is only possible if the call was |
|
|
144 |
done using __WUNTRACED__. |
|
|
145 |
|
|
|
146 |
|
|
|
147 |
__WSTOPSIG(__''status''__)__ |
|
|
148 |
|
|
|
149 |
|
|
|
150 |
returns the number of the signal which caused the child to |
|
|
151 |
stop. This macro can only be evaluated if __WIFSTOPPED__ |
|
|
152 |
returned non-zero. |
|
|
153 |
|
|
|
154 |
|
|
|
155 |
Some versions of Unix (e.g. Linux, Solaris, but not AIX, |
|
|
156 |
SunOS) also define a macro |
|
|
157 |
__WCOREDUMP(__''status''__)__ to test whether the |
|
|
158 |
child process dumped core. Only use this enclosed in #ifdef |
|
|
159 |
WCOREDUMP ... #endif. |
|
|
160 |
!!RETURN VALUE |
|
|
161 |
|
|
|
162 |
|
|
|
163 |
The process ID of the child which exited, or zero if |
|
|
164 |
__WNOHANG__ was used and no child was available, or -1 on |
|
|
165 |
error (in which case ''errno'' is set to an appropriate |
|
|
166 |
value). |
|
|
167 |
!!ERRORS |
|
|
168 |
|
|
|
169 |
|
|
|
170 |
__ECHILD__ |
|
|
171 |
|
|
|
172 |
|
|
|
173 |
if the process specified in ''pid'' does not exist or is |
|
|
174 |
not a child of the calling process. (This can happen for |
|
|
175 |
one's own child if the action for SIGCHLD is set to SIG_IGN. |
|
|
176 |
See also the NOTES section about threads.) |
|
|
177 |
|
|
|
178 |
|
|
|
179 |
__EINVAL__ |
|
|
180 |
|
|
|
181 |
|
|
|
182 |
if the ''options'' argument was invalid. |
|
|
183 |
|
|
|
184 |
|
|
|
185 |
__EINTR__ |
|
|
186 |
|
|
|
187 |
|
|
|
188 |
if __WNOHANG__ was not set and an unblocked signal or a |
|
|
189 |
__SIGCHLD__ was caught. |
|
|
190 |
!!NOTES |
|
|
191 |
|
|
|
192 |
|
|
|
193 |
The Single Unix Specification describes a flag SA_NOCLDWAIT |
|
|
194 |
(not present under Linux) such that if either this flag is |
|
|
195 |
set, or the action for SIGCHLD is set to SIG_IGN (which, by |
|
|
196 |
the way, is not allowed by POSIX), then children that exit |
|
|
197 |
do not become zombies and a call to ''wait()'' or |
|
|
198 |
''waitpid()'' will block until all children have exited, |
|
|
199 |
and then fail with ''errno'' set to ECHILD. |
|
|
200 |
|
|
|
201 |
|
|
|
202 |
In the Linux kernel, a kernel-scheduled thread is not a |
|
|
203 |
distinct construct from a process. Instead, a thread is |
|
|
204 |
simply a process that is created using the Linux-unique |
|
|
205 |
clone(2) system call; other routines such as the portable |
4 |
perry |
206 |
pthread_create(3) call are implemented using |
1 |
perry |
207 |
clone(2). Thus, if two threads A and B are siblings, |
|
|
208 |
then thread A cannot wait on any processes forked by thread |
|
|
209 |
B or its descendents, because an uncle cannot wait on his |
|
|
210 |
nephews. In some other Unix-like systems, where multiple |
|
|
211 |
threads are implemented as belonging to a single process, |
|
|
212 |
thread A can wait on any processes forked by sibling thread |
|
|
213 |
B; you will have to rewrite any code that makes this |
|
|
214 |
assumption for it to work on Linux. |
|
|
215 |
!!CONFORMING TO |
|
|
216 |
|
|
|
217 |
|
|
|
218 |
SVr4, POSIX.1 |
|
|
219 |
!!SEE ALSO |
|
|
220 |
|
|
|
221 |
|
4 |
perry |
222 |
clone(2), signal(2), wait4(2), |
|
|
223 |
pthread_create(3), signal(7) |
1 |
perry |
224 |
---- |