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-><HEAD
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->A Sample Program with Two Threads</TITLE
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-TITLE="Building and Running Sample Applications"
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-TITLE="Building and Running Sample Applications"
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-TITLE="More Features — Clocks and Alarm
-Handlers"
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->Chapter 13. Building and Running Sample Applications</TD
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-><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
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