MSGRCV(2) | System Calls Manual | MSGRCV(2) |
msgrcv
—
#include <sys/msg.h>
ssize_t
msgrcv
(int
msqid, void *msgp,
size_t msgsz,
long msgtyp,
int msgflg);
msgrcv
() function receives a message from the
message queue specified in msqid, and places it into the
user-defined structure pointed to by msgp. This
structure must contain a first field of type long that will
indicate the user-defined type of the message. The remaining fields will
contain the contents of the message. The following is an example of what this
user-defined structure might look like:
struct mymsg { long mtype; /* message type */ char mtext[1]; /* body of message */ };
mtype is an integer greater than 0 that can
be used to select messages. mtext is an array of
bytes, with size up to the system limit MSGMAX
.
The value of msgtyp has one of the following meanings:
The argument msgsz specifies the size in
bytes of mtext. If the received message has a length
greater than msgsz it will be silently truncated if
the MSG_NOERROR
flag is set in
msgflg, otherwise an error will be returned.
If no matching message is present on the message queue specified
by msqid, the behaviour of
msgrcv
() depends on whether the
IPC_NOWAIT
flag is set in
msgflg or not. If IPC_NOWAIT
is set, then msgrcv
() will immediately return a
value of -1 and set errno to
EAGAIN
. If IPC_NOWAIT
is not
set, the calling process will block until:
EIDRM
.EINTR
.If a message is successfully received, the data structure associated with msqid is updated as follows:
msgrcv
() returns the number
of bytes received and placed into the mtext field of the
structure pointed to by msgp. Otherwise, -1 is returned,
and errno set to indicate the error.
msgrcv
() will fail if:
E2BIG
]MSG_NOERROR
flag was not set in msgflg.EACCES
]EAGAIN
]IPC_NOWAIT
is set in
msgflg.EFAULT
]EIDRM
]EINTR
]EINVAL
]The message queue was removed while
msgrcv
() was waiting for a message of the
requested type to become available in it.
msgsz is greater than
SSIZE_MAX
.
ENOMSG
]IPC_NOWAIT
is set.msgrcv
system call conforms to
X/Open System Interfaces and Headers Issue 5
(“XSH5”).
July 24, 2013 | NetBSD 9.0 |