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improved doc on preemptive callback mode

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Jeff Hill
2007-01-11 21:37:43 +00:00
parent 287743f140
commit 47f5203faa
1 changed files with 24 additions and 9 deletions
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src/ca/CAref.html
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@@ -2303,15 +2303,30 @@ callbacks will be called preemptively from more than one thread.</p>
<h4>Arguments</h4>
<dl>
<dt><code>SELECT</code></dt>
<dd>Specifies if preemptive callback is allowed. If it is allowed your
callbacks might be called when the thread that calls this routine is
not executing in the CA client library. Programmers who are unfamiliar
with mutual exclusion locking in a multi-threaded environment should
specify <code>ca_disable_preemptive_callback</code>. If
ca_enable_preemptive_callback is specified then CA client background
activities, such as connection management, will proceed even if the
thread that calls this routine is not executing in the CA client
library.</dd>
<dd>This argument specifies if preemptive invocation of callback
functions is allowed. If so your callback functions might be called
when the thread that calls this routine is not executing in the CA
client library. There are two implications to consider. </dd>
<dd><p>First, if preemptive callback mode is enabled the developer must
provide mutual exclusion protection for his data structures. In this
mode it's possible for two threads to touch the application's data
structures at once: this might be the initializing thread (the thread
that called ca_context_create) and also a private thread created by the
CA client library for the purpose of receiving network messages and
calling callbacks. It might be prudent for developers who are
unfamiliar with mutual exclusion locking in a multi-threaded
environment to specify <code>ca_disable_preemptive_callback</code>. </p>
<p>Second, if preemptive callback mode is enabled the application is no
longer burdened with the necessity of periodically polling the CA
client library in order that it might take care of its background
activities. If <code>ca_enable_preemptive_callback</code> is specified
then CA client background activities, such as connection management,
will proceed even if the thread that calls this routine is not
executing in the CA client library. Furthermore, in preemptive callback
mode callbacks might be called with less latency because the library is
not required to wait until the initializing thread (the thread that
called ca_context_create) is executing within the CA client library.</p>
</dd>
</dl>
<h4>Returns</h4>