resmgr_msgread()

Updated: May 06, 2022

Read a message from a client

Synopsis:

#include <sys/iofunc.h>
#include <sys/resmgr.h>

ssize_t resmgr_msgread( resmgr_context_t * ctp,
                        void * msg,
                        size_t size,
                        size_t offset );

Arguments:

ctp
A pointer to a resmgr_context_t structure that the resource-manager library uses to pass context information between functions. This function extracts the rcvid from this structure.
msg
A pointer to a buffer where the function can store the data.
size
The number of bytes that you want to read. These functions don't let you read past the end of the thread's message; they return the number of bytes actually read.
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 resmgr_msgread() function is a convenience function that you can use in a resource manager instead of MsgRead(). However, for efficiency, you should use resmgr_msgget() instead.

You'll use resmgr_msgread() when you handle combine messages, where the offset of the rest of the message that's to be read is additionally offset by previous combine message elements. For more information, see Layers in a resource manager in the Bones of a Resource Manager chapter of Writing a Resource Manager.

Returns:

The same values as MsgRead(): the number of bytes read, or -1 if an error occurs (errno is set).

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.
ESRCH
The thread indicated by ctp->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.
ETIMEDOUT
A kernel timeout unblocked the call. See TimerTimeout().

Classification:

QNX Neutrino

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