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<!-- Copyright (C) 2003 Red Hat, Inc. --> <!-- This material may be distributed only subject to the terms --> <!-- and conditions set forth in the Open Publication License, v1.0 --> <!-- or later (the latest version is presently available at --> <!-- http://www.opencontent.org/openpub/). --> <!-- Distribution of the work or derivative of the work in any --> <!-- standard (paper) book form is prohibited unless prior --> <!-- permission is obtained from the copyright holder. --> <HTML ><HEAD ><TITLE >A Sample Program with Two Threads</TITLE ><meta name="MSSmartTagsPreventParsing" content="TRUE"> <META NAME="GENERATOR" CONTENT="Modular DocBook HTML Stylesheet Version 1.76b+ "><LINK REL="HOME" TITLE="eCos User Guide" HREF="ecos-user-guide.html"><LINK REL="UP" TITLE="Building and Running Sample Applications" HREF="building-and-running-sample-appliations.html"><LINK REL="PREVIOUS" TITLE="Building and Running Sample Applications" HREF="building-and-running-sample-appliations.html"><LINK REL="NEXT" TITLE="More Features — Clocks and Alarm Handlers" HREF="clocks-and-alarm-handlers.html"></HEAD ><BODY CLASS="SECT1" BGCOLOR="#FFFFFF" TEXT="#000000" LINK="#0000FF" VLINK="#840084" ALINK="#0000FF" ><DIV CLASS="NAVHEADER" ><TABLE SUMMARY="Header navigation table" WIDTH="100%" BORDER="0" CELLPADDING="0" CELLSPACING="0" ><TR ><TH COLSPAN="3" ALIGN="center" >eCos User Guide</TH ></TR ><TR ><TD WIDTH="10%" ALIGN="left" VALIGN="bottom" ><A HREF="building-and-running-sample-appliations.html" ACCESSKEY="P" >Prev</A ></TD ><TD WIDTH="80%" ALIGN="center" VALIGN="bottom" >Chapter 13. Building and Running Sample Applications</TD ><TD WIDTH="10%" ALIGN="right" VALIGN="bottom" ><A HREF="clocks-and-alarm-handlers.html" ACCESSKEY="N" >Next</A ></TD ></TR ></TABLE ><HR ALIGN="LEFT" WIDTH="100%"></DIV ><DIV CLASS="SECT1" ><H1 CLASS="SECT1" ><A NAME="SAMPLE-TWOTHREADS">A Sample Program with Two Threads</H1 ><P >Below is a program that uses some of <SPAN CLASS="PRODUCTNAME" >eCos</SPAN >' system calls. It creates two threads, each of which goes into an infinite loop in which it sleeps for a while (using cyg_thread_delay()). This code is found in the file <TT CLASS="FILENAME" >twothreads.c</TT > in the examples directory.</P ><DIV CLASS="SECT2" ><H2 CLASS="SECT2" ><A NAME="AEN871"><SPAN CLASS="PRODUCTNAME" >eCos</SPAN > two-threaded program listing</H2 ><TABLE BORDER="5" BGCOLOR="#E0E0F0" WIDTH="70%" ><TR ><TD ><PRE CLASS="PROGRAMLISTING" >#include <cyg/kernel/kapi.h> #include <stdio.h> #include <math.h> #include <stdlib.h> /* now declare (and allocate space for) some kernel objects, like the two threads we will use */ cyg_thread thread_s[2]; /* space for two thread objects */ char stack[2][4096]; /* space for two 4K stacks */ /* now the handles for the threads */ cyg_handle_t simple_threadA, simple_threadB; /* and now variables for the procedure which is the thread */ cyg_thread_entry_t simple_program; /* and now a mutex to protect calls to the C library */ cyg_mutex_t cliblock; /* we install our own startup routine which sets up threads */ void cyg_user_start(void) { printf("Entering twothreads' cyg_user_start() function\n"); cyg_mutex_init(&cliblock); cyg_thread_create(4, simple_program, (cyg_addrword_t) 0, "Thread A", (void *) stack[0], 4096, &simple_threadA, &thread_s[0]); cyg_thread_create(4, simple_program, (cyg_addrword_t) 1, "Thread B", (void *) stack[1], 4096, &simple_threadB, &thread_s[1]); cyg_thread_resume(simple_threadA); cyg_thread_resume(simple_threadB); } /* this is a simple program which runs in a thread */ void simple_program(cyg_addrword_t data) { int message = (int) data; int delay; printf("Beginning execution; thread data is %d\n", message); cyg_thread_delay(200); for (;;) { delay = 200 + (rand() % 50); /* note: printf() must be protected by a call to cyg_mutex_lock() */ cyg_mutex_lock(&cliblock); { printf("Thread %d: and now a delay of %d clock ticks\n", message, delay); } cyg_mutex_unlock(&cliblock); cyg_thread_delay(delay); } }</PRE ></TD ></TR ></TABLE ><P >When you run the program (by typing <B CLASS="COMMAND" >continue</B > at the (<SPAN CLASS="emphasis" ><I CLASS="EMPHASIS" >gdb</I ></SPAN >) prompt) the output should look like this:</P ><TABLE BORDER="5" BGCOLOR="#E0E0F0" WIDTH="70%" ><TR ><TD ><PRE CLASS="PROGRAMLISTING" >Starting program: <TT CLASS="REPLACEABLE" ><I >BASE_DIR</I ></TT >/examples/twothreads.exe Entering twothreads' cyg_user_start() function Beginning execution; thread data is 0 Beginning execution; thread data is 1 Thread 0: and now a delay of 240 clock ticks Thread 1: and now a delay of 225 clock ticks Thread 1: and now a delay of 234 clock ticks Thread 0: and now a delay of 231 clock ticks Thread 1: and now a delay of 224 clock ticks Thread 0: and now a delay of 249 clock ticks Thread 1: and now a delay of 202 clock ticks Thread 0: and now a delay of 235 clock ticks</PRE ></TD ></TR ></TABLE ><DIV CLASS="NOTE" ><BLOCKQUOTE CLASS="NOTE" ><P ><B >Note: </B >When running in a simulator the delays might be quite long. On a hardware board (where the clock speed is 100 ticks/second) the delays should average to about 2.25 seconds. In simulation, the delay will depend on the speed of the host processor and will almost always be much slower than the actual board. You might want to reduce the delay parameter when running in simulation.</P ></BLOCKQUOTE ></DIV ><P ><A HREF="sample-twothreads.html#FIGURE-TWOTHREADS-WITH-SIMPLE-PRINTS" >Figure 13-1</A > shows how this multitasking program executes. Note that apart from the thread creation system calls, this program also creates and uses a <SPAN CLASS="emphasis" ><I CLASS="EMPHASIS" >mutex</I ></SPAN > for synchronization between the <TT CLASS="FUNCTION" >printf()</TT > calls in the two threads. This is because the C library standard I/O (by default) is configured not to be thread-safe, which means that if more than one thread is using standard I/O they might corrupt each other. This is fixed by a mutual exclusion (or <SPAN CLASS="emphasis" ><I CLASS="EMPHASIS" >mutex</I ></SPAN >) lockout mechanism: the threads do not call <TT CLASS="FUNCTION" >printf()</TT > until <TT CLASS="FUNCTION" >cyg_mutex_lock()</TT > has returned, which only happens when the other thread calls <TT CLASS="FUNCTION" >cyg_mutex_unlock()</TT >.</P ><P >You could avoid using the mutex by configuring the C library to be thread-safe (by selecting the component <TT CLASS="LITERAL" >CYGSEM_LIBC_STDIO_THREAD_SAFE_STREAMS</TT >).</P ><DIV CLASS="FIGURE" ><A NAME="FIGURE-TWOTHREADS-WITH-SIMPLE-PRINTS"><P ><B >Figure 13-1. Two threads with simple print statements after random delays</B ></P ><P ><IMG SRC="pix/twothreads2.png"></P ></DIV ></DIV ></DIV ><DIV CLASS="NAVFOOTER" ><HR ALIGN="LEFT" WIDTH="100%"><TABLE SUMMARY="Footer navigation table" WIDTH="100%" BORDER="0" CELLPADDING="0" CELLSPACING="0" ><TR ><TD WIDTH="33%" ALIGN="left" VALIGN="top" ><A HREF="building-and-running-sample-appliations.html" ACCESSKEY="P" >Prev</A ></TD ><TD WIDTH="34%" ALIGN="center" VALIGN="top" ><A HREF="ecos-user-guide.html" ACCESSKEY="H" >Home</A ></TD ><TD WIDTH="33%" ALIGN="right" VALIGN="top" ><A HREF="clocks-and-alarm-handlers.html" ACCESSKEY="N" >Next</A ></TD ></TR ><TR ><TD WIDTH="33%" ALIGN="left" VALIGN="top" >Building and Running Sample Applications</TD ><TD WIDTH="34%" ALIGN="center" VALIGN="top" ><A HREF="building-and-running-sample-appliations.html" ACCESSKEY="U" >Up</A ></TD ><TD WIDTH="33%" ALIGN="right" VALIGN="top" >More Features — Clocks and Alarm Handlers</TD ></TR ></TABLE ></DIV ></BODY ></HTML >
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