7 Nokia Corporation - initial contribution. |
7 Nokia Corporation - initial contribution. |
8 Contributors: |
8 Contributors: |
9 --> |
9 --> |
10 <!DOCTYPE concept |
10 <!DOCTYPE concept |
11 PUBLIC "-//OASIS//DTD DITA Concept//EN" "concept.dtd"> |
11 PUBLIC "-//OASIS//DTD DITA Concept//EN" "concept.dtd"> |
12 <concept id="GUID-056B9A65-EC59-4B2E-9F10-E487343B5F5F" xml:lang="en"><title>SemaphoreExample: |
12 <concept id="GUID-056B9A65-EC59-4B2E-9F10-E487343B5F5F" xml:lang="en"><title>SemaphoreExample: thread synchronisation using semaphores</title><shortdesc>Explains how to use Semaphores to achieve thread synchronization.</shortdesc><prolog><metadata><keywords/></metadata></prolog><conbody> |
13 thread synchronisation using semaphores</title><shortdesc>Explains how to use Semaphores to achieve thread synchronization.</shortdesc><prolog><metadata><keywords/></metadata></prolog><conbody> |
13 <p>It is recommended to use semaphores instead of thread priorities |
14 <p>It is recommended to use semaphores instead of thread priorities for the |
14 for the following reasons:<ul> |
15 following reasons:<ul> |
15 <li><p> In a uniprocessor environment, setting the thread priorities |
16 <li><p> In a uniprocessor environment, setting the thread priorities does |
16 does not guarantee prioritized or serialized execution.</p></li> |
17 not guarantee prioritized or serialized execution.</p></li> |
17 <li><p>In a multiprocessor or SMP environment, thread priorities are |
18 <li><p>In a multiprocessor or SMP environment, thread priorities are irrelevant |
18 irrelevant as multiple threads can run simultaneously.</p></li> |
19 as multiple threads can run simultaneously.</p></li> |
|
20 </ul></p> |
19 </ul></p> |
21 <section id="GUID-48668C9B-6B42-4FE8-899B-403D5EB5FB53"><title>Download</title> <p>Click on the following link to download |
20 <section id="GUID-48668C9B-6B42-4FE8-899B-403D5EB5FB53"><title>Download</title> <p>Click on the following link to download the example: <xref href="guid-6013a680-57f9-415b-8851-c4fa63356636/zips/guid-34775913-c5c2-41ba-a591-827039bbe7af.zip" scope="external">SemaphoreExample.zip</xref></p><p>Click: <xref href="guid-6013a680-57f9-415b-8851-c4fa63356636/guid-34775913-c5c2-41ba-a591-827039bbe7af.html" scope="peer">browse</xref> to view the example code. </p></section> |
22 the example: <xref href="guid-6013a680-57f9-415b-8851-c4fa63356636/zips/guid-34775913-c5c2-41ba-a591-827039bbe7af.zip" scope="external">SemaphoreExample.zip</xref></p><p>Click: <xref href="guid-6013a680-57f9-415b-8851-c4fa63356636/guid-34775913-c5c2-41ba-a591-827039bbe7af.html" scope="peer">browse</xref> to view the example code. </p></section> |
21 <section id="GUID-2E531F3D-EEC8-40FD-9F32-2071FDECAE61"><title>Description: </title><p> The example creates a database containing a table of three columns |
23 <section id="GUID-2E531F3D-EEC8-40FD-9F32-2071FDECAE61"><title>Description: </title><p> The example creates a database containing |
22 with integer entries.</p><p> The example creates two threads:</p><ul> |
24 a table of three columns with integer entries.</p><p> The example creates |
23 <li><p><codeph>WriterThread</codeph>: This thread calls a periodic |
25 two threads:</p><ul> |
24 function at an interval of one second, and in each iteration it inserts |
26 <li><p><codeph>WriterThread</codeph>: This thread calls a periodic function |
25 one row of integers in the table. </p></li> |
27 at an interval of one second, and in each iteration it inserts one row of |
26 <li><p><codeph>ReaderThread</codeph>: This thread also calls a periodic |
28 integers in the table. </p></li> |
27 function at an interval of one second, and in each iteration it reads |
29 <li><p><codeph>ReaderThread</codeph>: This thread also calls a periodic function |
28 one row of integers following the last row read.</p></li> |
30 at an interval of one second, and in each iteration it reads one row of integers |
29 </ul><p> The example uses a macro <codeph>USE_SEMAPHORE</codeph> to |
31 following the last row read.</p></li> |
30 show the difference between the code using semaphores and the code |
32 </ul><p> The example uses a macro <codeph>USE_SEMAPHORE</codeph> to show the |
31 which doesn't use semaphores. When not using semaphores, it is not |
33 difference between the code using semaphores and the code which doesn't use |
32 guaranteed that the <codeph>ReaderThread</codeph> will be able to |
34 semaphores. When not using semaphores, it is not guaranteed that the <codeph>ReaderThread</codeph> will |
33 read the database because in an SMP environment, data may not yet |
35 be able to read the database because in an SMP environment, data may not yet |
34 have been written by the <codeph>WriterThread</codeph>.</p><p>Using |
36 have been written by the <codeph>WriterThread</codeph>.</p><p>Using a semaphore |
35 a semaphore serializes the thread execution. The read operation waits |
37 serializes the thread execution. The read operation waits on the semaphore |
36 on the semaphore until it gets a signal from the write operation. |
38 until it gets a signal from the write operation. This ensures that the <codeph>ReaderThread</codeph> only |
37 This ensures that the <codeph>ReaderThread</codeph> only reads a row |
39 reads a row from the database after the <codeph>WriterThread</codeph> has |
38 from the database after the <codeph>WriterThread</codeph> has written |
40 written it. </p></section> |
39 it. </p></section> |
41 <section id="GUID-07CAD3CA-86DB-4245-8565-C618E59718A5"><title>Class summary</title><ul> |
40 <section id="GUID-07CAD3CA-86DB-4245-8565-C618E59718A5"><title>Class |
|
41 summary</title><ul> |
42 <li><p><xref href="GUID-B0E661BC-4058-3256-B9C3-5A4FD52F6DE5.dita"><apiname>RThread</apiname></xref> - A handle to a thread.</p></li> |
42 <li><p><xref href="GUID-B0E661BC-4058-3256-B9C3-5A4FD52F6DE5.dita"><apiname>RThread</apiname></xref> - A handle to a thread.</p></li> |
43 <li><p><xref href="GUID-F4A68645-2265-307F-B951-8295827E000B.dita"><apiname>RDbStoreDatabase</apiname></xref> - DBMS Store database implementation</p></li> |
43 <li><p><xref href="GUID-F4A68645-2265-307F-B951-8295827E000B.dita"><apiname>RDbStoreDatabase</apiname></xref> - DBMS Store database implementation</p></li> |
44 <li><p><xref href="GUID-AED27A76-3645-3A04-B80D-10473D9C5A27.dita"><apiname>RSemaphore</apiname></xref> - Used for thread synchronization. </p></li> |
44 <li><p><xref href="GUID-AED27A76-3645-3A04-B80D-10473D9C5A27.dita"><apiname>RSemaphore</apiname></xref> - Used for thread synchronization. </p></li> |
45 </ul></section> |
45 </ul></section> |
46 <section id="GUID-863B0EDF-F3F8-4345-9FEE-824350A2DBCE"><title>Building and configuring</title> <p>To build the example: </p> <ul> |
46 <section id="GUID-863B0EDF-F3F8-4345-9FEE-824350A2DBCE"><title>Building |
47 <li id="GUID-037442C7-2436-5152-9A3E-9DC0B4283A9C"><p>The example builds an |
47 and configuring</title> <p>To build the example: </p> <ul> |
48 executable called <filepath>semaphoreexample.exe</filepath> in the standard |
48 <li id="GUID-037442C7-2436-5152-9A3E-9DC0B4283A9C"><p>The example |
49 location. </p> </li> |
49 builds an executable called <filepath>semaphoreexample.exe</filepath> in the standard location. </p> </li> |
50 <li id="GUID-B7C849B9-0885-5253-A78B-71854F86D772"><p>You can build the example |
50 <li id="GUID-B7C849B9-0885-5253-A78B-71854F86D772"><p>You can build |
51 from your IDE or the command line. </p> <p>If you use an IDE, import the <filepath>bld.inf</filepath> file |
51 the example from your IDE or the command line. </p> <p>If you use |
52 of the example into your IDE, and use the build command of the IDE. </p> <p>If |
52 an IDE, import the <filepath>bld.inf</filepath> file of the example |
53 you use the command line, open a command prompt, and set the current directory |
53 into your IDE, and use the build command of the IDE. </p> <p>If you |
54 to the source code directory of the example. You can then build the example |
54 use the command line, open a command prompt, and set the current directory |
55 with the SBSv1 build tools with the following commands: </p> <p><userinput>bldmake |
55 to the source code directory of the example. You can then build the |
56 bldfiles</userinput> </p> <p><userinput>abld build</userinput> </p> <p><xref href="GUID-793A5EF9-CC16-5EEB-9011-6431EA76EB15.dita">How to use bldmake</xref> and <xref href="GUID-B6B54E07-3B34-5D5C-8815-93383FA8FB4B.dita">How to use abld</xref> describe |
56 example with the SBSv1 build tools with the following commands: </p> <p><userinput>bldmake bldfiles</userinput> </p> <p><userinput>abld |
57 how to use the SBSv1 build tools. </p> </li> |
57 build</userinput> .</p> </li> |
58 </ul> </section> |
58 </ul> </section> |
59 <section id="GUID-278DD8CF-28AF-4826-B938-20EC19F3A5B0"><title>Running the example</title> <p>The example code contains a |
59 <section id="GUID-278DD8CF-28AF-4826-B938-20EC19F3A5B0"><title>Running |
60 macro<codeph>USE_SEMAPHORE</codeph> in the <filepath>mmp</filepath> file. |
60 the example</title> <p>The example code contains a macro<codeph>USE_SEMAPHORE</codeph> in the <filepath>mmp</filepath> file. By default it is commented |
61 By default it is commented out and on execution the example runs without using |
61 out and on execution the example runs without using semaphores; the |
62 semaphores; the macro should be uncommented to use semaphores. The console |
62 macro should be uncommented to use semaphores. The console output |
63 output will generally look the same whether using semaphores or not if there |
63 will generally look the same whether using semaphores or not if there |
64 is a single processor, but differences will occur in an SMP environment. Run |
64 is a single processor, but differences will occur in an SMP environment. |
65 the example following the instructions provided in the console. </p> </section> |
65 Run the example following the instructions provided in the console. </p> </section> |
66 </conbody></concept> |
66 </conbody></concept> |