MsgReceivePulse(), MsgReceivePulse_r()

Receive a pulse on a channel

Synopsis:

#include <sys/neutrino.h>

int MsgReceivePulse( int chid,
                     void * pulse,
                     int bytes,
                     struct _msg_info * info );

int MsgReceivePulse_r( int chid,
                       void * pulse,
                       int bytes,
                       struct _msg_info * info );

The ID of a channel that you established by calling ChannelCreate(), or -1 to dissociate the thread from the last channel it received on (see “Server boost” in the Interprocess Communication chapter of the System Architecture guide).

pulse

A void * pointer to a struct _pulse structure where the function can store the received data.

If this buffer isn't big enough to contain a struct _pulse structure, you'll get an EFAULT.

bytes

The size of the buffer.

info

The function doesn't update this structure, so you typically pass NULL for this argument.

Library:

libc

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

Description:

The MsgReceivePulse() and MsgReceivePulse_r() kernel calls wait for a pulse to arrive on the channel identified by chid and place the received data in the buffer pointed to by pulse. If the buffer is large enough, the number of bytes written to it is the size of a struct _pulse structure.

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

If a pulse is waiting on the channel when you call MsgReceivePulse(), the calling thread doesn't block, and the pulse is immediately copied. If a pulse isn't waiting, the calling thread enters the RECEIVE-blocked state until a pulse arrives.

If multiple pulses are sent to a channel without a thread waiting to receive them, the pulses are queued in priority order.

When a thread receives a pulse:

The kernel space allocated to hold the pulse is immediately released.
The memory that pulse points to contains a pulse message of type struct _pulse.
The thread's effective priority might change. For more information, see “Priority inheritance and messages” in the Interprocess Communication (IPC) chapter of the System Architecture guide.

Don't reply to a pulse.

Blocking states

STATE_RECEIVE: There's no pulse waiting.

Returns:

The only difference between MsgReceivePulse() and MsgReceivePulse_r() is the way they indicate errors. On success, they both return 0.

If an error occurred:

MsgReceivePulse() returns -1 and sets errno.
MsgReceivePulse_r() returns the negative of a value from the Errors section. This function doesn't set errno.

Errors:

EFAULT: A fault occurred when the kernel tried to access the buffer provided, or the size of the receive buffer is less than the size of a struct _pulse. The pulse is lost in this case.
EINTR: The call was interrupted by a signal.
ESRCH: The channel indicated by chid doesn't exist.
ETIMEDOUT: A kernel timeout unblocked the call. See TimerTimeout().

Classification:

QNX Neutrino

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