Wait for a message or pulse on a channel
#include <sys/neutrino.h> int MsgReceivev( int chid, const iov_t * riov, int rparts, struct _msg_info * info ); int MsgReceivev_r( int chid, const iov_t * riov, int rparts, struct _msg_info * info );
Use the -l c option to qcc to link against this library. This library is usually included automatically.
The MsgReceivev() and MsgReceivev_r() kernel calls wait for a message or pulse to arrive on the channel identified by chid and place the received data in the array of buffers pointed to by riov.
These functions are identical, except in the way they indicate errors; see the Returns section for details.
The number of bytes transferred is the minimum of that specified by both the sender and the receiver. The received data isn't allowed to overflow the receive buffer area provided.
|The first buffer of the IOV (input/output vector) must be big enough to contain a pulse. If it isn't, the functions indicate an error of EFAULT.|
If a message is waiting on the channel when you call MsgReceivev(), the calling thread won't block, and the message is immediately copied. If a message isn't waiting, the calling thread enters the RECEIVE-blocked state until a message arrives.
If multiple messages are sent to a channel without a thread waiting to receive them, the messages are queued in priority order.
|The thread's effective priority might change when it receives a message. For more information, see “Priority inheritance and messages” in the Interprocess Communication (IPC) chapter of the System Architecture guide.|
If you pass a non-NULL pointer for info, the functions store additional information about the message and the thread that sent it in the _msg_info structure that info points to. You can get this information later by calling MsgInfo().
On success, MsgReceivev() and MsgReceivev_r() return:
|Don't reply to a pulse.|
|STATE_RECEIVE||There's no message waiting.|
The only difference between MsgReceivev() and MsgReceivev_r() is the way they indicate errors. On success, both functions return a positive rcvid if they received a message, or 0 if they received a pulse.
If an error occurs:
ChannelCreate(), _msg_info, MsgInfo(), MsgRead(), MsgReadv(), MsgReceive(), MsgReceivePulse(), MsgReceivePulsev(), MsgReply(), MsgReplyv(), MsgWrite(), MsgWritev(), _pulse, TimerTimeout()
Message Passing chapter of Getting Started with QNX Neutrino