TimerTimeout(), TimerTimeout_r()

Set a timeout on a blocking state

Synopsis:

#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 );

Arguments:

id

The type of timer 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 — 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.

flags

Flags that specify which states the timeout applies to. For the list and description of applicable states, see the section “Timeout states.”

notify

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.

ntime

The timeout (in nanoseconds).

otime

NULL, or a pointer to a location where the function can store the time remaining in the sleep.

Library:

libc

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

Description:

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.

---

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

---

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

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:

_NTO_TIMEOUT_CONDVAR

Timeout on STATE_CONDVAR.

_NTO_TIMEOUT_JOIN

Timeout on STATE_JOIN.

_NTO_TIMEOUT_INTR

Timeout on STATE_INTR.

_NTO_TIMEOUT_MUTEX

Timeout on STATE_MUTEX.

_NTO_TIMEOUT_RECEIVE

Timeout on STATE_RECEIVE.

_NTO_TIMEOUT_REPLY

Timeout on STATE_REPLY.

_NTO_TIMEOUT_SEM

Timeout on STATE_SEM.

_NTO_TIMEOUT_SEND

Timeout on STATE_SEND.

_NTO_TIMEOUT_SIGSUSPEND

Timeout on STATE_SIGSUSPEND.

_NTO_TIMEOUT_SIGWAITINFO

Timeout on STATE_SIGWAITINFO.

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

_NTO_TIMEOUT_SEND | _NTO_TIMEOUT_REPLY

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

Armed

The kernel attempts to enter a blocking state specified in flags.

Released

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, 
              _NTO_TIMEOUT_SEND | _NTO_TIMEOUT_REPLY,
              &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:

• SIGEV_SIGNAL
• SIGEV_SIGNAL_CODE
• SIGEV_SIGNAL_THREAD
• SIGEV_PULSE
• SIGEV_UNBLOCK
• SIGEV_INTR

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.

---

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:

• Is specified by the ntime argument (the number of nanoseconds).
• Is relative to the current time (when TimerTimeout() is called), unless flags includes TIMER_ABSTIME, which makes the timeout occur at the absolute time set in ntime.
• Occurs on a clock tick (see ClockPeriod()) so the actual wakeup time is a minimum of:

  ( ntime ) / ( size of timer tick ) nanoseconds
        

---

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:

TimerTimeout( CLOCK_REALTIME, _NTO_TIMEOUT_NANOSLEEP, 
              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:

STATE_NANOSLEEP

The calling thread blocks for the requested time period.

Returns:

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

TimerTimeout()

The previous flags. If an error occurs, -1 is returned and errno is set.

TimerTimeout_r()

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

Errors:

EAGAIN

All kernel timer entries are in use.

EFAULT

A fault occurred when the kernel tried to access ntime, otime, or notify.

EINTR

The call was interrupted by a signal.

EINVAL

Invalid timer value id.

Classification:

QNX Neutrino

Caveats:

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