MsgReadv(), MsgReadv_r()

Read data from a message

Synopsis:

#include <sys/neutrino.h>

ssize_t MsgReadv( int rcvid,
                  const iov_t* riov,
                  size_t rparts,
                  size_t offset );

ssize_t MsgReadv_r( int rcvid,
                    const iov_t* riov,
                    size_t rparts,
                    size_t offset );

Arguments:

rcvid
The value returned by MsgReceive*() when you received the message.
riov
An array of buffers where the functions can store the data.
rparts
The number of elements in the riov array.
offset
An offset into the thread's send message that indicates where you want to start reading the data.

Library:

libc

Use the -l c option to qcc to link against this library. This library is usually included automatically.

Description:

The MsgReadv() and MsgReadv_r() kernel calls read data from a message sent by a thread identified by rcvid. The thread being read from must not have been replied to and will be in the REPLY-blocked state. Any thread in the receiving process is free to read the message.

These functions are identical except in the way they indicate errors. See the Returns section for details.

The data transfer occurs immediately and the thread doesn't block. The state of the sending thread doesn't change.

An attempt to read past the end of the thread's message results in fewer bytes returned than requested.

You'll use these functions in these situations:

When you're finished using MsgReadv(), you must use MsgReply*() to ready the REPLY-blocked process and complete the message exchange.

Blocking states

None. In the network case, lower priority threads may run.

Returns:

The number of bytes read. If an error occurs:

Errors:

EDEADLK
A deadlock occurred. You can avoid a deadlock by setting the _NTO_CHF_MSG_PAUSING flag when you create a channel; for more information, see ChannelCreate() and MsgPause().
EFAULT
A fault occurred in a server's address space when the kernel tried to access the server's message buffers.
EOVERFLOW
The sum of the IOV lengths exceeds INT_MAX, or the number of parts exceeds 524288.
ESRCH
The thread indicated by rcvid doesn't exist, is no longer REPLY-blocked on the channel, or the connection was detached.
ESRVRFAULT
A fault occurred when the kernel tried to access the buffers provided.

Classification:

QNX Neutrino

Safety:  
Cancellation point No
Interrupt handler No
Signal handler Yes
Thread Yes