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 clock to use to implement the timeout; one of:
  • CLOCK_REALTIME — the standard POSIX-defined clock. Timers based on this clock wake up the processor if it's in a power-saving mode.
  • CLOCK_SOFTTIME — (a QNX Neutrino extension) this clock is active only when the processor isn't in a power-saving mode. For example, an application using a CLOCK_SOFTTIME timer to sleep wouldn't wake up the processor when the application was due to wake up. This will allow the processor to enter a power-saving mode.

    While the processor isn't in a power-saving mode, CLOCK_SOFTTIME behaves the same as CLOCK_REALTIME.

  • CLOCK_MONOTONIC — this clock always increases at a constant rate and can't be adjusted.

For more information about the different clocks, see "Other clock sources" in the Clocks, Timers, and Getting a Kick Every So Often of Getting Started with QNX Neutrino.

Flags that control the function's behavior. The value can be either:
  • TIMER_TOLERANCE to specify the amount of the tolerance to allow the kernel in low-power situations


  • a combination of zero or more bits that specify which states the timeout applies to (see below). You can also OR in the following bits:
    • TIMER_ABSTIME — set an absolute expiration time. If you don't set this bit, the function sets a relative expiration time.
    • TIMER_PRECISE — override any default tolerance that was set for the process (see procmgr_timer_tolerance()).
NULL, or a pointer to a sigevent structure that contains the event to act on when the timeout expires; see below.

If you specify TIMER_TOLERANCE in the flags, this argument must be NULL.

NULL, or a pointer to the timeout or timer tolerance, in nanoseconds. If this argument is NULL, the timeout occurs immediately (see below), or the function doesn't change the timer tolerance, depending on the flags.
NULL, or a pointer to a location where the function can store some data, depending on the flags:
  • TIMER_TOLERANCE — the previous timer tolerance.
  • _NTO_TIMEOUT_NANOSLEEP — 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: The timer_timeout() function is a cover for TimerTimeout() that uses a timespec structure instead of a uint64_t to specify the timeout.

The following table shows the blocking states that are entered as a result of certain kernel calls, along with the corresponding timeout state bits that you can use in the flags argument:

Call Blocking state Timeout state
MsgReceive(), MsgReceivev(), MsgReceivePulse(), MsgReceivePulsev() STATE_RECEIVE _NTO_TIMEOUT_RECEIVE
MsgDeliverEvent(), MsgError(), MsgRead(), MsgReadv(), MsgReply(), MsgReplyv(), MsgWrite(), MsgWritev() STATE_REPLY _NTO_TIMEOUT_REPLY
MsgSend(), MsgSendnc(), MsgSendsv(), MsgSendsvnc(), MsgSendv(), MsgSendvnc(), MsgSendvs(), MsgSendvsnc() STATE_SEND or STATE_REPLY _NTO_TIMEOUT_SEND or _NTO_TIMEOUT_REPLY
MsgSendPulse() STATE_NET_SEND or STATE_NET_REPLY Timing out on these states isn't supported
SignalKill() STATE_NET_SEND or STATE_NET_REPLY Timing out on these states isn't supported
ThreadCtl() STATE_WAITPAGE Timing out on this state isn't supported

For example, to set a timeout on MsgSendv(), specify _NTO_TIMEOUT_SEND | _NTO_TIMEOUT_REPLY for the flags argument.

Here's what happens to the timer:

Note: A relative timeout starts when you call TimerTimeout(), not when the blocking state is entered. It's possible to get preempted after calling TimerTimeout() but before the blocking kernel call.

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 time out. For example:

event.sigev_notify = SIGEV_UNBLOCK;

timeout = 10 * 1000000000;

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

There's one exception to this rule: if you want to set the timer tolerance, you need to call TimerTimeout() twice, once with flags set to TIMER_TOLERANCE, and once to set the timeout. It doesn't matter which order you do this in.

If you call TimerTimeout() followed by a kernel call that can't cause the thread to block (e.g., ClockId()), the results are undefined.

If a 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.

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 unblock only a MsgReceivev(). If you pass NULL for notify, SIGEV_UNBLOCK is assumed. In this case, a timed-out kernel call returns failure with an error of ETIMEDOUT.

Note: MsgSend*() doesn't unblock on SIGEV_UNBLOCK if the server has already received the message via MsgReceive*() 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 MsgReply*() or MsgError().

The timeout

The id argument specifies the clock to use to implement the timeout. 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 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 while waiting for messages.

If you set flags to _NTO_TIMEOUT_NANOSLEEP, then:

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 previous flags. If an error occurs:


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 arguments:
  • The id argument doesn't specify a valid clock ID.
  • If you specified TIMER_TOLERANCE in the flags, you also set other bits in the flags, or notify isn't NULL.


QNX Neutrino

Cancellation point No
Interrupt handler No
Signal handler Yes
Thread Yes