86 you do not because the thread is not blocked until after the kernel lock is |
86 you do not because the thread is not blocked until after the kernel lock is |
87 released. </p> <p>Be aware however that there may be situations where you |
87 released. </p> <p>Be aware however that there may be situations where you |
88 already have the kernel lock, or in the case of IDFCs, you do not need to |
88 already have the kernel lock, or in the case of IDFCs, you do not need to |
89 acquire it as no preemption can occur. In these cases, you just call <xref href="GUID-D5B555DA-3D17-3ED2-A931-CB35BD93A953.dita#GUID-D5B555DA-3D17-3ED2-A931-CB35BD93A953/GUID-76E5AE32-9A70-344A-9E6B-5B439622715A"><apiname>NFastMutex::Wait()</apiname></xref> and <xref href="GUID-D5B555DA-3D17-3ED2-A931-CB35BD93A953.dita#GUID-D5B555DA-3D17-3ED2-A931-CB35BD93A953/GUID-CA8C65D8-E59A-385A-92B8-2B22A4A2F1CB"><apiname>NFastMutex::Signal()</apiname></xref>. </p> <p>The following diagram illustrates the general principle: </p> <fig id="GUID-30A0EA62-83CF-5AB9-A07E-525D0972E55B"> |
89 acquire it as no preemption can occur. In these cases, you just call <xref href="GUID-D5B555DA-3D17-3ED2-A931-CB35BD93A953.dita#GUID-D5B555DA-3D17-3ED2-A931-CB35BD93A953/GUID-76E5AE32-9A70-344A-9E6B-5B439622715A"><apiname>NFastMutex::Wait()</apiname></xref> and <xref href="GUID-D5B555DA-3D17-3ED2-A931-CB35BD93A953.dita#GUID-D5B555DA-3D17-3ED2-A931-CB35BD93A953/GUID-CA8C65D8-E59A-385A-92B8-2B22A4A2F1CB"><apiname>NFastMutex::Signal()</apiname></xref>. </p> <p>The following diagram illustrates the general principle: </p> <fig id="GUID-30A0EA62-83CF-5AB9-A07E-525D0972E55B"> |
90 <title>Fast mutex</title> |
90 <title>Fast mutex</title> |
91 <image href="GUID-3AFE0D8B-FB9B-5355-A63B-FB71DD13E7D0_d0e300993_href.png" placement="inline"/> |
91 <image href="GUID-3AFE0D8B-FB9B-5355-A63B-FB71DD13E7D0_d0e306985_href.png" placement="inline"/> |
92 </fig> <p>There are a number of assumptions here, one of which is that the |
92 </fig> <p>There are a number of assumptions here, one of which is that the |
93 priorities are such that thread T1 does not run until a reschedule occurs, |
93 priorities are such that thread T1 does not run until a reschedule occurs, |
94 after T2 has been interrupted. </p> <p id="GUID-111E74A3-8442-5598-8BB9-F78E2A77610A"><b>Example |
94 after T2 has been interrupted. </p> <p id="GUID-111E74A3-8442-5598-8BB9-F78E2A77610A"><b>Example |
95 using NFastmutex to protect a critical region</b> </p> <p>The file <filepath>...\f32test\nkern\d_implicit.cpp</filepath> is |
95 using NFastmutex to protect a critical region</b> </p> <p>The file <filepath>...\f32test\nkern\d_implicit.cpp</filepath> is |
96 a device driver that contains 3 threads and 3 separate sub-tests. The third |
96 a device driver that contains 3 threads and 3 separate sub-tests. The third |
487 platform semaphore operations are protected by the <xref href="GUID-EAA6A9FB-A470-550C-B7B4-FF68A733A2D5.dita#GUID-EAA6A9FB-A470-550C-B7B4-FF68A733A2D5/GUID-A0FB7718-F39C-5FB3-B67C-430B490F6430">system lock</xref> fast mutex rather than by locking the kernel. To guarantee |
487 platform semaphore operations are protected by the <xref href="GUID-EAA6A9FB-A470-550C-B7B4-FF68A733A2D5.dita#GUID-EAA6A9FB-A470-550C-B7B4-FF68A733A2D5/GUID-A0FB7718-F39C-5FB3-B67C-430B490F6430">system lock</xref> fast mutex rather than by locking the kernel. To guarantee |
488 this, semaphore operations are done through kernel functions. </p> <p>Although |
488 this, semaphore operations are done through kernel functions. </p> <p>Although |
489 somewhat artificial, and not based on real code, the following diagram nevertheless |
489 somewhat artificial, and not based on real code, the following diagram nevertheless |
490 shows the basic idea behind Symbian platform semaphores. </p> <fig id="GUID-505BC4A5-BBCB-5A63-9795-C751719661BB"> |
490 shows the basic idea behind Symbian platform semaphores. </p> <fig id="GUID-505BC4A5-BBCB-5A63-9795-C751719661BB"> |
491 <title>Symbian platform semaphore</title> |
491 <title>Symbian platform semaphore</title> |
492 <image href="GUID-0FE0B646-A62F-55A8-A6E6-587D0909CE19_d0e301860_href.png" placement="inline"/> |
492 <image href="GUID-0FE0B646-A62F-55A8-A6E6-587D0909CE19_d0e307852_href.png" placement="inline"/> |
493 </fig> <p id="GUID-6131CDB0-6249-5B9A-A969-9B25F8BCECF5"><b>Rules</b> </p> <p>There |
493 </fig> <p id="GUID-6131CDB0-6249-5B9A-A969-9B25F8BCECF5"><b>Rules</b> </p> <p>There |
494 are a few rules about the use of Symbian platform semaphores: </p> <ul> |
494 are a few rules about the use of Symbian platform semaphores: </p> <ul> |
495 <li id="GUID-B850F00A-D7E6-5542-9D9D-F07F2625E29B"><p>Only Symbian platform |
495 <li id="GUID-B850F00A-D7E6-5542-9D9D-F07F2625E29B"><p>Only Symbian platform |
496 threads are allowed to use Symbian platform semaphores </p> </li> |
496 threads are allowed to use Symbian platform semaphores </p> </li> |
497 <li id="GUID-C848306E-7407-5397-8638-DB6AB7250A4E"><p>An IDFC is not allowed |
497 <li id="GUID-C848306E-7407-5397-8638-DB6AB7250A4E"><p>An IDFC is not allowed |