1semop(2) System Calls semop(2)
2
6 semop, semtimedop - semaphore operations
7
9 #include <sys/types.h>
10 #include <sys/ipc.h>
11 #include <sys/sem.h>
12 int semop(int semid, struct sembuf *sops, size_t nsops);
14 int semtimedop(int semid, struct sembuf *sops, size_t nsops,
17 const struct timespec *timeout);
18
21 The semop() function is used to perform atomically an array of sema‐
22 phore operations on the set of semaphores associated with the semaphore
23 identifier specified by semid. The sops argument is a pointer to the
24 array of semaphore-operation structures. The nsops argument is the num‐
25 ber of such structures in the array.
26 Each sembuf structure contains the following members:
29 short sem_num; /* semaphore number */
31 short sem_op; /* semaphore operation */
32 short sem_flg; /* operation flags */
33 Each semaphore operation specified by sem_op is performed on the corre‐
37 sponding semaphore specified by semid and sem_num. The permission
38 required for a semaphore operation is given as {token}, where token is
39 the type of permission needed. The types of permission are interpreted
40 as follows:
41 00400 READ by user
43 00200 ALTER by user
44 00040 READ by group
45 00020 ALTER by group
46 00004 READ by others
47 00002 ALTER by others
48 See the Semaphore Operation Permissions section of Intro(2) for more
52 information.
53 A process maintains a value, semadj, for each semaphore it modifies.
56 This value contains the cumulative effect of operations the process has
57 performed on an individual semaphore with the SEM_UNDO flag set (so
58 that they can be undone if the process terminates unexpectedly). The
59 value of semadj can affect the behavior of calls to semop(), semtime‐
60 dop(), exit(), and _exit() (the latter two functions documented on
61 exit(2)), but is otherwise unobservable. See below for details.
62 The sem_op member specifies one of three semaphore operations:
65 1. The sem_op member is a negative integer; {ALTER}
67 o If semval (see Intro(2)) is greater than or equal to the
69 absolute value of sem_op, the absolute value of sem_op
70 is subtracted from semval. Also, if (sem_flg&SEM_UNDO)
71 is true, the absolute value of sem_op is added to the
72 calling process's semadj value (see exit(2)) for the
73 specified semaphore.
74 o If semval is less than the absolute value of sem_op and
76 (sem_flg&IPC_NOWAIT) is true, semop() returns immedi‐
77 ately.
78 o If semval is less than the absolute value of sem_op and
80 (sem_flg&IPC_NOWAIT) is false, semop() increments the
81 semncnt associated with the specified semaphore and sus‐
82 pends execution of the calling thread until one of the
83 following conditions occur:
84 o The value of semval becomes greater than or equal to
86 the absolute value of sem_op. When this occurs, the
87 value of semncnt associated with the specified sema‐
88 phore is decremented, the absolute value of sem_op
89 is subtracted from semval and, if (sem_flg&SEM_UNDO)
90 is true, the absolute value of sem_op is added to
91 the calling process's semadj value for the specified
92 semaphore.
93 o The semid for which the calling thread is awaiting
95 action is removed from the system (see semctl(2)).
96 When this occurs, errno is set to EIDRM and −1 is
97 returned.
98 o The calling thread receives a signal that is to be
100 caught. When this occurs, the value of semncnt asso‐
101 ciated with the specified semaphore is decremented,
102 and the calling thread resumes execution in the man‐
103 ner prescribed in sigaction(2).
104 2. The sem_op member is a positive integer; {ALTER}
106 The value of sem_op is added to semval and, if
108 (sem_flg&SEM_UNDO) is true, the value of sem_op is sub‐
109 tracted from the calling process's semadj value for the
110 specified semaphore.
111 3. The sem_op member is 0; {READ}
113 o If semval is 0, semop() returns immediately.
115 o If semval is not equal to 0 and (sem_flg&IPC_NOWAIT) is
117 true, semop() returns immediately.
118 o If semval is not equal to 0 and (sem_flg&IPC_NOWAIT) is
120 false, semop() increments the semzcnt associated with
121 the specified semaphore and suspends execution of the
122 calling thread until one of the following occurs:
123 o The value of semval becomes 0, at which time the
125 value of semzcnt associated with the specified sema‐
126 phore is set to 0 and all processes waiting on sem‐
127 val to become 0 are awakened.
128 o The semid for which the calling thread is awaiting
130 action is removed from the system. When this occurs,
131 errno is set to EIDRM and −1 is returned.
132 o The calling thread receives a signal that is to be
134 caught. When this occurs, the value of semzcnt asso‐
135 ciated with the specified semaphore is decremented,
136 and the calling thread resumes execution in the man‐
137 ner prescribed in sigaction(2).
138 Upon successful completion, the value of sempid for each semaphore
141 specified in the array pointed to by sops is set to the process ID of
142 the calling process.
143 The semtimedop() function behaves as semop() except when it must sus‐
146 pend execution of the calling process to complete its operation. If
147 semtimedop() must suspend the calling process after the time interval
148 specified in timeout expires, or if the timeout expires while the
149 process is suspended, semtimedop() returns with an error. If the time‐
150 spec structure pointed to by timeout is zero-valued and semtimedop()
151 needs to suspend the calling process to complete the requested opera‐
152 tion(s), it returns immediately with an error. If timeout is the NULL
153 pointer, the behavior of semtimedop() is identical to that of semop().
154
156 Upon successful completion, 0 is returned. Otherwise, −1 is returned
157 and errno is set to indicate the error.
158
160 The semop() and semtimedop() functions will fail if:
161 E2BIG The nsops argument is greater than the system-imposed maxi‐
163 mum. See NOTES.
164 EACCES Operation permission is denied to the calling process (see
167 Intro(2)).
168 EAGAIN The operation would result in suspension of the calling
171 process but (sem_flg&IPC_NOWAIT) is true.
172 EFAULT The sops argument points to an illegal address.
175 EFBIG The value of sem_num is less than 0 or greater than or equal
178 to the number of semaphores in the set associated with semid.
179 EIDRM A semid was removed from the system.
182 EINTR A signal was received.
185 EINVAL The semid argument is not a valid semaphore identifier, or
188 the number of individual semaphores for which the calling
189 process requests a SEM_UNDO operation would exceed the sys‐
190 tem-imposed limit. Solaris does not impose a limit on the
191 number of individual semaphores for which the calling process
192 requests a SEM_UNDO operation.
193 ENOSPC The limit on the number of individual processes requesting a
196 SEM_UNDO operation would be exceeded. Solaris does not impose
197 a limit on the number of individual processes requesting an
198 SEM_UNDO operation.
199 ERANGE An operation would cause a semval or a semadj value to over‐
202 flow the system-imposed limit.
203 The semtimedop() function will fail if:
207 EAGAIN The timeout expired before the requested operation could be
209 completed.
210 The semtimedop() function will fail if one of the following is
214 detected:
215 EFAULT The timeout argument points to an illegal address.
217 EINVAL The timeout argument specified a tv_sec or tv_nsec value less
220 than 0, or a tv_nsec value greater than or equal to 1000 mil‐
221 lion.
222
225 See attributes(5) for descriptions of the following attributes:
226 ┌─────────────────────────────┬─────────────────────────────┐
231 │ ATTRIBUTE TYPE │ ATTRIBUTE VALUE │
232 ├─────────────────────────────┼─────────────────────────────┤
233 │Interface Stability │semop() is Standard. │
234 └─────────────────────────────┴─────────────────────────────┘
235
237 ipcs(1), rctladm(1M), Intro(2), exec(2), exit(2), fork(2), semctl(2),
238 semget(2), setrctl(2), sigaction(2), attributes(5), standards(5)
239
241 The system-imposed maximum on nsops for a semaphore identifier is the
242 minimum enforced value of the process.max-sem-ops resource control of
243 the creating process at the time semget(2) was used to allocate the
244 identifier.
245 See rctladm(1M) and setrctl(2) for information about using resource
248 controls.
249SunOS 5.11 12 May 2006 semop(2)