Caution: This version of this document is no longer maintained. For the latest documentation, see

TimerTimeout(), TimerTimeout_r()

Set a timeout on a blocking state


#include <sys/neutrino.h>

int TimerTimeout( clockid_t id,
                  int flags,
                  const struct sigevent * notify,
                  const uint64_t * ntime,
                  uint64_t * otime );

int TimerTimeout_r( clockid_t id,
                    int flags,
                    const struct sigevent * notify,
                    const uint64_t * ntime,
                    uint64_t * otime );


The type of timer to implement the timeout; one of:
Flags that specify which states the timeout applies to. For the list and description of applicable states, see the section Timeout states.”
A pointer to a sigevent structure that contains the event to act on when the timeout expires. See Event types for the list of recommended event types.
The timeout (in nanoseconds).
NULL, or a pointer to a location where the function can store the time remaining in the sleep.



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


The TimerTimeout() and TimerTimeout_r() kernel calls set a timeout on any kernel blocking state.

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

Note: Instead of using these kernel calls directly, consider calling timer_timeout().

These blocking states are entered as a result of the following kernel calls:

Call Blocking state
InterruptWait() STATE_INTR
SyncCondvarWait() STATE_CONDVAR
SyncMutexLock() STATE_MUTEX
SyncSemWait() STATE_SEM
ThreadJoin() STATE_JOIN

Timeout states

You can specify which states the timeout should apply to via a bitmask passed in the flags argument. The bits are defined by the following constants:

Timeout on STATE_JOIN.
Timeout on STATE_INTR.
Timeout on STATE_MUTEX.
Timeout on STATE_REPLY.
Timeout on STATE_SEM.
Timeout on STATE_SEND.

For example, to set a timeout on MsgSendv(), specify:


Once a timeout is specified using TimerTimeout(), it's armed and released under the following conditions:

The kernel attempts to enter a blocking state specified in flags.
One of the above kernel calls completed without blocking, or the kernel call blocks but unblocks before the timeout expires, or the timeout expires.

TimerTimeout() always operates on a one-shot basis. When one of the above kernel calls returns (or is interrupted by a signal), the timeout request is removed from the system. Only one timeout per thread may be in effect at a time. A second call to TimerTimeout(), without calling one of the above kernel functions, replaces the existing timeout on that thread. A call with flags set to zero ensures that a timeout won't occur on any state. This is the default when a thread is created.

Always call TimerTimeout() just before the function that you wish to timeout. For example:

event.sigev_notify = SIGEV_UNBLOCK;

timeout = 10×1000000000;

TimerTimeout( CLOCK_REALTIME, 
              &event, &timeout, NULL );
MsgSendv( coid, NULL, 0, NULL, 0 );

If the signal handler is called between the calls to TimerTimeout() and MsgSendv(), the TimerTimeout() values are saved during the signal handler and then are restored when the signal handler exits.

Event types

If the timeout expires, the kernel acts upon the event specified in the sigevent structure pointed to by the notify argument. We recommend the following event types in this case:

Only SIGEV_UNBLOCK guarantees that the kernel call unblocks. A signal may be ignored, blocked, or accepted by another thread, and a pulse can only unblock a MsgReceivev(). If you pass NULL for event, SIGEV_UNBLOCK is assumed. In this case, a timed out kernel call returns failure with an error of ETIMEDOUT.

Note: MsgSendv() doesn't unblock on SIGEV_UNBLOCK if the server has already received the message via MsgReceivev() and has specified _NTO_CHF_UNBLOCK in the flags argument to its ChannelCreate() call. In this case, it's up to the server to do a MsgReplyv().

The timeout

The type of timer used to implement the timeout is specified with the id argument.

The timeout:

Note: Because of the nature of time measurement, the timer might actually expire later than the specified time. For more information, see the Tick, Tock: Understanding the Neutrino Microkernel's Concept of Time chapter of the QNX Neutrino Programmer's Guide.

If you don't wish to block for any time, you can pass a NULL for ntime, in which case no timer is used, the event is assumed to be SIGEV_UNBLOCK, and an attempt to enter a blocking state as set by flags immediately returns with ETIMEDOUT. Although a questionable practice, you can use it to poll potential blocking kernel calls. For example, you can poll for messages using MsgReceivev() with an immediate timeout. A much better approach is to use multiple threads and have one block waiting for messages.

If you set flags to _NTO_TIMEOUT_NANOSLEEP, then these calls block in the STATE_NANOSLEEP state until the timeout (or a signal that unblocks the thread) occurs. You can use this to implement an efficient kernel sleep as follows:

              NULL, ntime, otime );

If otime isn't NULL and the sleep is unblocked by a signal, it contains the time remaining in the sleep.

The actual timeout that occurred is returned in otime. The resolution of otime for both timer_timeout() and TimerTimeout() functions is in nanoseconds. The difference, however, for otime in these two functions is in the format. For timer_timeout(), the otime is a pointer to timespec structure with two integers, whereas for TimerTimeout(), the pointer is of uint64_t type.

Blocking states

These calls don't block unless you specify _NTO_TIMEOUT_NANOSLEEP in flags. In this case, the calls block as follows:

The calling thread blocks for the requested time period.


The only difference between these functions is the way they indicate errors:

The previous flags. If an error occurs, -1 is returned and errno is set.
The previous flags. This function does NOT set errno. If an error occurs, the negative of a value from the Errors section is returned.


All kernel timer entries are in use.
A fault occurred when the kernel tried to access ntime, otime, or notify.
The call was interrupted by a signal.
Invalid timer value id.


QNX Neutrino

Cancellation point No
Interrupt handler No
Signal handler Yes
Thread Yes


The timeout value starts timing out when TimerTimeout() is called, not when the blocking state is entered. It might be possible to get preempted after calling TimerTimeout() but before the blocking kernel call.

See also:

sigevent, timer_timeout(), TimerCreate(), TimerInfo()

Clocks, Timers, and Getting a Kick Every So Often chapter of Getting Started with QNX Neutrino