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<concept id="GUID-B4039418-6499-555D-AC24-9B49161299F2" xml:lang="en"><title>Creating

a Periodic Timer</title><prolog><metadata><keywords/></metadata></prolog><conbody>

<p>You can use a periodic timer to provide repeated signals to your process. </p>

<p>The following example illustrates a periodic timer with a delay of a second

and a repeating interval of ten milliseconds. It also configures a thread

function as the timer expiry notification using <codeph>SIGEV_THREAD</codeph>. </p>

<p>The following example code performs the following tasks: </p>

<ol id="GUID-B648631F-8CC2-5304-B2DC-6A9293385E3E">

<li id="GUID-228938F5-3F52-5853-96FC-2556650A617A"><p>Creates a notification

function (thread function) that must be invoked after timer expiry. </p> </li>

<li id="GUID-7F02B8B1-7AE3-566A-A864-A64B45837C79"><p>Sets the thread priority

to <b>255</b> using the thread scheduling parameters (<codeph>struct sched_param</codeph>).

This ensures that the thread function has the highest priority when it is

invoked as a result of a timer expiry. </p> </li>

<li id="GUID-14F0D0AC-65EF-56B6-B82A-EC41C4DDA94F"><p>Creates a timer based

on the current system time (<codeph>CLOCK_REALTIME</codeph>) and a notification

function (<codeph>struct              sigevent sig</codeph>) that must be

invoked when the timer expires. </p> </li>

<li id="GUID-0A915D17-5113-563B-9CE4-7A7B7B7D7B23"><p>Defines the input values

for <xref href="GUID-344F836B-FAC8-344A-B458-0CEFB714ADEB.dita"><apiname>timer_settime()</apiname></xref>. The key input values are the timer

value (<codeph>in.it_value.tv_sec = 1;</codeph>) and the interval (<codeph>in.it_interval.tv_nsec

= 100000000;</codeph>). The periodic timer will expire after a second and

then invoke the notification function every one-tenth of a second until it

is destroyed. </p> </li>

<li id="GUID-126A5B20-133D-585A-9FF9-9CB5456D2D71"><p>Starts the periodic

timer using <xref href="GUID-344F836B-FAC8-344A-B458-0CEFB714ADEB.dita"><apiname>timer_settime()</apiname></xref>. </p> </li>

<li id="GUID-FD1EEA8C-3215-5DBE-BB29-47576DED3955"><p>Uses <codeph>sleep(2)</codeph> to

pause the program execution for two seconds before destroying the timer. </p> </li>

</ol>

<codeblock id="GUID-60B88762-E6C3-52F8-8DBC-E77D70B03FAE" xml:space="preserve">#include &lt;time.h&gt;

#include <stdio.h>

#include <signal.h>

#include <pthread.h>

#include <unistd.h>

#include <errno.h>

static int i = 0;

//Thread function to be invoked when the periodic timer expires

void sighler (union sigval val)

    {

    printf("Handler entered with value :%d for %d times\n", val.sival_int, ++i);

    }

int main()

    {

    int Ret;

    pthread_attr_t attr;

    pthread_attr_init( &attr );

    struct sched_param parm;

    parm.sched_priority = 255;

    pthread_attr_setschedparam(&attr, &parm);

    struct sigevent sig;

    sig.sigev_notify = SIGEV_THREAD;

    sig.sigev_notify_function = sighler;

    sig.sigev_value.sival_int =20;

    sig.sigev_notify_attributes = &attr;

    //create a new timer.

    timer_t timerid;

    Ret = timer_create(CLOCK_REALTIME, &sig, &timerid);

    if (Ret == 0)

        {

        struct itimerspec in, out;

        in.it_value.tv_sec = 1;

        in.it_value.tv_nsec = 0;

        in.it_interval.tv_sec = 0;

        in.it_interval.tv_nsec = 100000000;

        //issue the periodic timer request here.

        Ret = timer_settime(timerid, 0, &in, &out);

        if(Ret == 0)

            sleep(2);

        else

            printf("timer_settime() failed with %d\n", errno);

        //delete the timer.

        timer_delete(timerid);

        }

    else

    printf("timer_create() failed with %d\n", errno);

    return Ret;

    }</codeblock>

<p>The output of the above program is: </p>

<codeblock id="GUID-313450D1-6766-58C6-933C-49AD55A5D985" xml:space="preserve">Handler entered with value :20 for 1 times

Handler entered with value :20 for 2 times

Handler entered with value :20 for 3 times

Handler entered with value :20 for 4 times

Handler entered with value :20 for 5 times

Handler entered with value :20 for 6 times

Handler entered with value :20 for 7 times

Handler entered with value :20 for 8 times</codeblock>

<p> <b>Note:</b> Ideally, in the preceding output the handler must have entered <b>10</b> times.

This is not the case on the Symbian platform as there is some

latency due to the timer emulation solution and the underlying Symbian platform

clock resolution. </p>

</conbody></concept>