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1 <?xml version="1.0" encoding="utf-8"?> |
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2 <!-- Copyright (c) 2007-2010 Nokia Corporation and/or its subsidiary(-ies) All rights reserved. --> |
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3 <!-- This component and the accompanying materials are made available under the terms of the License |
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4 "Eclipse Public License v1.0" which accompanies this distribution, |
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5 and is available at the URL "http://www.eclipse.org/legal/epl-v10.html". --> |
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6 <!-- Initial Contributors: |
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7 Nokia Corporation - initial contribution. |
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8 Contributors: |
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9 --> |
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10 <!DOCTYPE concept |
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11 PUBLIC "-//OASIS//DTD DITA Concept//EN" "concept.dtd"> |
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12 <concept xml:lang="en" id="GUID-B4039418-6499-555D-AC24-9B49161299F2"><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 |
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13 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 <time.h> |
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14 #include <stdio.h> |
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15 #include <signal.h> |
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16 #include <pthread.h> |
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17 #include <unistd.h> |
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18 #include <errno.h> |
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19 static int i = 0; |
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20 |
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21 //Thread function to be invoked when the periodic timer expires |
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22 void sighler (union sigval val) |
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23 { |
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24 printf("Handler entered with value :%d for %d times\n", val.sival_int, ++i); |
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25 } |
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26 int main() |
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27 { |
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28 int Ret; |
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29 |
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30 pthread_attr_t attr; |
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31 pthread_attr_init( &attr ); |
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32 |
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33 struct sched_param parm; |
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34 parm.sched_priority = 255; |
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35 pthread_attr_setschedparam(&attr, &parm); |
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36 |
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37 struct sigevent sig; |
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38 sig.sigev_notify = SIGEV_THREAD; |
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39 sig.sigev_notify_function = sighler; |
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40 sig.sigev_value.sival_int =20; |
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41 sig.sigev_notify_attributes = &attr; |
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42 |
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43 //create a new timer. |
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44 timer_t timerid; |
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45 Ret = timer_create(CLOCK_REALTIME, &sig, &timerid); |
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46 if (Ret == 0) |
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47 { |
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48 struct itimerspec in, out; |
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49 in.it_value.tv_sec = 1; |
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50 in.it_value.tv_nsec = 0; |
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51 in.it_interval.tv_sec = 0; |
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52 in.it_interval.tv_nsec = 100000000; |
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53 //issue the periodic timer request here. |
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54 Ret = timer_settime(timerid, 0, &in, &out); |
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55 if(Ret == 0) |
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56 sleep(2); |
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57 else |
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58 printf("timer_settime() failed with %d\n", errno); |
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59 //delete the timer. |
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60 timer_delete(timerid); |
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61 } |
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62 else |
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63 printf("timer_create() failed with %d\n", errno); |
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64 return Ret; |
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65 }</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 |
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66 Handler entered with value :20 for 2 times |
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67 Handler entered with value :20 for 3 times |
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68 Handler entered with value :20 for 4 times |
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69 Handler entered with value :20 for 5 times |
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70 Handler entered with value :20 for 6 times |
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71 Handler entered with value :20 for 7 times |
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72 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 Symbian platform as there is some latency due to the timer emulation solution and the underlying Symbian platform clock resolution. </p> </conbody></concept> |