diff options
Diffstat (limited to 'doc/html/callbacks.html')
| -rw-r--r-- | doc/html/callbacks.html | 121 |
1 files changed, 0 insertions, 121 deletions
diff --git a/doc/html/callbacks.html b/doc/html/callbacks.html deleted file mode 100644 index 0275e75..0000000 --- a/doc/html/callbacks.html +++ /dev/null @@ -1,121 +0,0 @@ -<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN"> -<html> -<head> -<title>4.2 Callbacks </title> -<META NAME="description" CONTENT="4.2 Callbacks "> -<META NAME="keywords" CONTENT="pyOpenSSL"> -<META NAME="resource-type" CONTENT="document"> -<META NAME="distribution" CONTENT="global"> -<link rel="STYLESHEET" href="pyOpenSSL.css"> -<LINK REL="next" href="socket-methods.html"> -<LINK REL="previous" href="exceptions.html"> -<LINK REL="up" href="internals.html"> -<LINK REL="next" href="socket-methods.html"> -</head> -<body> -<DIV CLASS="navigation"> -<table align="center" width="100%" cellpadding="0" cellspacing="2"> -<tr> -<td><A href="exceptions.html"><img src="previous.gif" - border="0" height="32" - alt="Previous Page" width="32"></A></td> -<td><A href="internals.html"><img src="up.gif" - border="0" height="32" - alt="Up One Level" width="32"></A></td> -<td><A href="socket-methods.html"><img src="next.gif" - border="0" height="32" - alt="Next Page" width="32"></A></td> -<td align="center" width="100%">Python OpenSSL Manual</td> -<td><A href="contents.html"><img src="contents.gif" - border="0" height="32" - alt="Contents" width="32"></A></td> -<td><img src="blank.gif" - border="0" height="32" - alt="" width="32"></td> -<td><img src="blank.gif" - border="0" height="32" - alt="" width="32"></td> -</tr></table> -<b class="navlabel">Previous:</b> <a class="sectref" href="exceptions.html">4.1 Exceptions</A> -<b class="navlabel">Up:</b> <a class="sectref" href="internals.html">4 Internals</A> -<b class="navlabel">Next:</b> <a class="sectref" href="socket-methods.html">4.3 Acessing Socket Methods</A> -<br><hr> -</DIV> -<!--End of Navigation Panel--> - -<H2><A NAME="SECTION000520000000000000000"> </A> -<BR> -4.2 Callbacks -</H2> - -<P> -There are a number of problems with callbacks. First of all, OpenSSL is written -as a C library, it's not meant to have Python callbacks, so a way around that -is needed. Another problem is thread support. A lot of the OpenSSL I/O -functions can block if the socket is in blocking mode, and then you want other -Python threads to be able to do other things. The real trouble is if you've -released the global CPython interpreter lock to do a potentially blocking -operation, and the operation calls a callback. Then we must take the GIL back, -since calling Python APIs without holding it is not allowed. - -<P> -There are two solutions to the first problem, both of which are necessary. The -first solution to use is if the C callback allows ''userdata'' to be passed to -it (an arbitrary pointer normally). This is great! We can set our Python -function object as the real userdata and emulate userdata for the Python -function in another way. The other solution can be used if an object with an -''app_data'' system always is passed to the callback. For example, the SSL -object in OpenSSL has app_data functions and in e.g. the verification -callbacks, you can retrieve the related SSL object. What we do is to set our -wrapper <tt class="class">Connection</tt> object as app_data for the SSL object, and we can -easily find the Python callback. - -<P> -The other problem is solved using thread local variables. Whenever the GIL is -released before calling into an OpenSSL API, the PyThreadState pointer returned -by <tt class="cfunction">PyEval_SaveState</tt> is stored in a global thread local variable -(using Python's own TLS API, <tt class="cfunction">PyThread_set_key_value</tt>). When it is -necessary to re-acquire the GIL, either after the OpenSSL API returns or in a C -callback invoked by that OpenSSL API, the value of the thread local variable is -retrieved (<tt class="cfunction">PyThread_get_key_value</tt>) and used to re-acquire the GIL. -This allows Python threads to execute while OpenSSL APIs are running and allows -use of any particular pyOpenSSL object from any Python thread, since there is -no per-thread state associated with any of these objects and since OpenSSL is -threadsafe (as long as properly initialized, as pyOpenSSL initializes it). - -<P> - -<DIV CLASS="navigation"> -<p><hr> -<table align="center" width="100%" cellpadding="0" cellspacing="2"> -<tr> -<td><A href="exceptions.html"><img src="previous.gif" - border="0" height="32" - alt="Previous Page" width="32"></A></td> -<td><A href="internals.html"><img src="up.gif" - border="0" height="32" - alt="Up One Level" width="32"></A></td> -<td><A href="socket-methods.html"><img src="next.gif" - border="0" height="32" - alt="Next Page" width="32"></A></td> -<td align="center" width="100%">Python OpenSSL Manual</td> -<td><A href="contents.html"><img src="contents.gif" - border="0" height="32" - alt="Contents" width="32"></A></td> -<td><img src="blank.gif" - border="0" height="32" - alt="" width="32"></td> -<td><img src="blank.gif" - border="0" height="32" - alt="" width="32"></td> -</tr></table> -<b class="navlabel">Previous:</b> <a class="sectref" href="exceptions.html">4.1 Exceptions</A> -<b class="navlabel">Up:</b> <a class="sectref" href="internals.html">4 Internals</A> -<b class="navlabel">Next:</b> <a class="sectref" href="socket-methods.html">4.3 Acessing Socket Methods</A> -<hr> -<span class="release-info">Release 0.12.</span> -</DIV> -<!--End of Navigation Panel--> - -</BODY> -</HTML> |