1msgsnd(2) System Calls msgsnd(2)
2
6 msgsnd - message send operation
7
9 #include <sys/msg.h>
10 int msgsnd(int msqid, const void *msgp, size_t msgsz, int msgflg);
12
15 The msgsnd() function is used to send a message to the queue associated
16 with the message queue identifier specified by msqid.
17 The msgp argument points to a user-defined buffer that must contain
20 first a field of type long int that will specify the type of the mes‐
21 sage, and then a data portion that will hold the data bytes of the mes‐
22 sage. The structure below is an example of what this user-defined buf‐
23 fer might look like:
24 struct mymsg {
26 long mtype; /* message type */
27 char mtext[1]; /* message text */
28 }
29 The mtype member is a non-zero positive type long int that can be used
33 by the receiving process for message selection.
34 The mtext member is any text of length msgsz bytes. The msgsz argument
37 can range from 0 to a system-imposed maximum.
38 The msgflg argument specifies the action to be taken if one or more of
41 the following are true:
42 o The number of bytes already on the queue is equal to
44 msg_qbytes. See Intro(2).
45 o The total number of messages on the queue would exceed the
47 maximum allowed by the system. See NOTES.
48 These actions are as follows:
51 o If (msgflg&IPC_NOWAIT) is non-zero, the message will not be
53 sent and the calling process will return immediately.
54 o If (msgflg&IPC_NOWAIT) is 0, the calling process will sus‐
56 pend execution until one of the following occurs:
57 o The condition responsible for the suspension no longer
59 exists, in which case the message is sent.
60 o The message queue identifier msqid is removed from the
62 system (see msgctl(2)); when this occurs, errno is set
63 equal to EIDRM and −1 is returned.
64 o The calling process receives a signal that is to be
66 caught; in this case the message is not sent and the
67 calling process resumes execution in the manner pre‐
68 scribed in sigaction(2).
69 Upon successful completion, the following actions are taken with
72 respect to the data structure associated with msqid (see Intro(2)):
73 o msg_qnum is incremented by 1.
75 o msg_lspid is set equal to the process ID of the calling
77 process.
78 o msg_stime is set equal to the current time.
80
82 Upon successful completion, 0 is returned. Otherwise, −1 is returned,
83 no message is sent, and errno is set to indicate the error.
84
86 The msgsnd() function will fail if:
87 EACCES Operation permission is denied to the calling process. See
89 Intro(2).
90 EAGAIN The message cannot be sent for one of the reasons cited above
93 and (msgflg&IPC_NOWAIT) is non-zero.
94 EIDRM The message queue identifier msgid is removed from the sys‐
97 tem.
98 EINTR The msgsnd() function was interrupted by a signal.
101 EINVAL The value of msqid is not a valid message queue identifier,
104 or the value of mtype is less than 1.
105 The value of msgsz is less than 0 or greater than the system-
107 imposed limit.
108 The msgsnd() function may fail if:
112 EFAULT The msgp argument points to an illegal address.
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117 The value passed as the msgp argument should be converted to type void
118 *.
119
121 See attributes(5) for descriptions of the following attributes:
122 ┌─────────────────────────────┬─────────────────────────────┐
127 │ ATTRIBUTE TYPE │ ATTRIBUTE VALUE │
128 ├─────────────────────────────┼─────────────────────────────┤
129 │Interface Stability │Standard │
130 └─────────────────────────────┴─────────────────────────────┘
131
133 rctladm(1M), Intro(2), msgctl(2), msgget(2), msgrcv(2), setrctl(2),
134 sigaction(2), attributes(5), standards(5)
135
137 The maximum number of messages allowed on a message queue is the mini‐
138 mum enforced value of the process.max-msg-messages resource control of
139 the creating process at the time msgget(2) was used to allocate the
140 queue.
141 See rctladm(1M) and setrctl(2) for information about using resource
144 controls.
145SunOS 5.11 11 Feb 2003 msgsnd(2)