Mercurial > sdl-ios-xcode
annotate docs/html/sdlgeteventfilter.html @ 3069:caefe2344f65
Date: Thu, 27 Dec 2007 07:38:25 +0000
From: John Bartholomew
Subject: [SDL] SDL Semaphore implementation broken on Windows?
Hi,
Over the past couple of days, I've been battling with SDL, SDL_Mixer and SMPEG to try to find an audio hang bug. I believe I've found the problem, which I think is a race condition inside SDL's semaphore implementation (at least the Windows implementation). The semaphore code uses Windows' built in semaphore functions, but it also maintains a separate count value. This count value is updated with bare increment and decrement operations in SemPost and SemWaitTimeout - no locking primitives to protect them.
In tracking down the apparent audio bug, I found that at some point a semaphore's count value was being decremented to -1, which is clearly not a valid value for it to take.
I'm still not certain exactly what sequence of operations is occuring for this to happen, but I believe that overall it's a race condition between a thread calling SemPost (which increments the count) and the thread on the other end calling SemWait (which decrements it).
I will try to make a test case to verify this, but I'm not sure if I'll be able to (threading errors being difficult to reproduce even in the best circumstances).
However, assuming this is the cause of my problems, there is a very
simple fix:
Windows provides InterlockedIncrement() and InterlockedDecrement()
functions to perform increments and decrements which are guaranteed to be atomic. So the fix is in thread/win32/SDL_syssem.c: replace occurrences of --sem->count with InterlockedDecrement(&sem->count); and replace occurrences of ++sem->count with InterlockedIncrement(&sem->count);
This is using SDL v1.2.12, built with VC++ 2008 Express, running on a
Core 2 duo processor.
author | Sam Lantinga <slouken@libsdl.org> |
---|---|
date | Tue, 17 Feb 2009 05:39:18 +0000 |
parents | 355632dca928 |
children |
rev | line source |
---|---|
0 | 1 <HTML |
2 ><HEAD | |
3 ><TITLE | |
4 >SDL_GetEventFilter</TITLE | |
5 ><META | |
6 NAME="GENERATOR" | |
803
355632dca928
Updated SDL HTML documentation
Sam Lantinga <slouken@libsdl.org>
parents:
181
diff
changeset
|
7 CONTENT="Modular DocBook HTML Stylesheet Version 1.76b+ |
0 | 8 "><LINK |
9 REL="HOME" | |
10 TITLE="SDL Library Documentation" | |
11 HREF="index.html"><LINK | |
12 REL="UP" | |
13 TITLE="Event Functions." | |
14 HREF="eventfunctions.html"><LINK | |
15 REL="PREVIOUS" | |
16 TITLE="SDL_SetEventFilter" | |
17 HREF="sdlseteventfilter.html"><LINK | |
18 REL="NEXT" | |
19 TITLE="SDL_EventState" | |
20 HREF="sdleventstate.html"></HEAD | |
21 ><BODY | |
22 CLASS="REFENTRY" | |
23 BGCOLOR="#FFF8DC" | |
24 TEXT="#000000" | |
25 LINK="#0000ee" | |
26 VLINK="#551a8b" | |
27 ALINK="#ff0000" | |
28 ><DIV | |
29 CLASS="NAVHEADER" | |
30 ><TABLE | |
803
355632dca928
Updated SDL HTML documentation
Sam Lantinga <slouken@libsdl.org>
parents:
181
diff
changeset
|
31 SUMMARY="Header navigation table" |
0 | 32 WIDTH="100%" |
33 BORDER="0" | |
34 CELLPADDING="0" | |
35 CELLSPACING="0" | |
36 ><TR | |
37 ><TH | |
38 COLSPAN="3" | |
39 ALIGN="center" | |
40 >SDL Library Documentation</TH | |
41 ></TR | |
42 ><TR | |
43 ><TD | |
44 WIDTH="10%" | |
45 ALIGN="left" | |
46 VALIGN="bottom" | |
47 ><A | |
48 HREF="sdlseteventfilter.html" | |
803
355632dca928
Updated SDL HTML documentation
Sam Lantinga <slouken@libsdl.org>
parents:
181
diff
changeset
|
49 ACCESSKEY="P" |
0 | 50 >Prev</A |
51 ></TD | |
52 ><TD | |
53 WIDTH="80%" | |
54 ALIGN="center" | |
55 VALIGN="bottom" | |
56 ></TD | |
57 ><TD | |
58 WIDTH="10%" | |
59 ALIGN="right" | |
60 VALIGN="bottom" | |
61 ><A | |
62 HREF="sdleventstate.html" | |
803
355632dca928
Updated SDL HTML documentation
Sam Lantinga <slouken@libsdl.org>
parents:
181
diff
changeset
|
63 ACCESSKEY="N" |
0 | 64 >Next</A |
65 ></TD | |
66 ></TR | |
67 ></TABLE | |
68 ><HR | |
69 ALIGN="LEFT" | |
70 WIDTH="100%"></DIV | |
71 ><H1 | |
72 ><A | |
73 NAME="SDLGETEVENTFILTER" | |
803
355632dca928
Updated SDL HTML documentation
Sam Lantinga <slouken@libsdl.org>
parents:
181
diff
changeset
|
74 ></A |
355632dca928
Updated SDL HTML documentation
Sam Lantinga <slouken@libsdl.org>
parents:
181
diff
changeset
|
75 >SDL_GetEventFilter</H1 |
0 | 76 ><DIV |
77 CLASS="REFNAMEDIV" | |
78 ><A | |
803
355632dca928
Updated SDL HTML documentation
Sam Lantinga <slouken@libsdl.org>
parents:
181
diff
changeset
|
79 NAME="AEN5615" |
0 | 80 ></A |
81 ><H2 | |
82 >Name</H2 | |
83 >SDL_GetEventFilter -- Retrieves a pointer to he event filter</DIV | |
84 ><DIV | |
85 CLASS="REFSYNOPSISDIV" | |
86 ><A | |
803
355632dca928
Updated SDL HTML documentation
Sam Lantinga <slouken@libsdl.org>
parents:
181
diff
changeset
|
87 NAME="AEN5618" |
0 | 88 ></A |
89 ><H2 | |
90 >Synopsis</H2 | |
91 ><DIV | |
92 CLASS="FUNCSYNOPSIS" | |
93 ><A | |
803
355632dca928
Updated SDL HTML documentation
Sam Lantinga <slouken@libsdl.org>
parents:
181
diff
changeset
|
94 NAME="AEN5619" |
0 | 95 ></A |
96 ><P | |
97 ></P | |
98 ><PRE | |
99 CLASS="FUNCSYNOPSISINFO" | |
100 >#include "SDL.h"</PRE | |
101 ><P | |
102 ><CODE | |
103 ><CODE | |
104 CLASS="FUNCDEF" | |
105 >SDL_EventFilter <B | |
106 CLASS="FSFUNC" | |
107 >SDL_GetEventFilter</B | |
108 ></CODE | |
109 >(void);</CODE | |
110 ></P | |
111 ><P | |
112 ></P | |
113 ></DIV | |
114 ></DIV | |
115 ><DIV | |
116 CLASS="REFSECT1" | |
117 ><A | |
803
355632dca928
Updated SDL HTML documentation
Sam Lantinga <slouken@libsdl.org>
parents:
181
diff
changeset
|
118 NAME="AEN5625" |
0 | 119 ></A |
120 ><H2 | |
121 >Description</H2 | |
122 ><P | |
123 >This function retrieces a pointer to the event filter that was previously set using <A | |
124 HREF="sdlseteventfilter.html" | |
125 ><TT | |
126 CLASS="FUNCTION" | |
127 >SDL_SetEventFilter</TT | |
128 ></A | |
129 >. An SDL_EventFilter function is defined as: | |
130 <PRE | |
131 CLASS="PROGRAMLISTING" | |
132 >typedef int (*SDL_EventFilter)(const SDL_Event *event);</PRE | |
133 ></P | |
134 ></DIV | |
135 ><DIV | |
136 CLASS="REFSECT1" | |
137 ><A | |
803
355632dca928
Updated SDL HTML documentation
Sam Lantinga <slouken@libsdl.org>
parents:
181
diff
changeset
|
138 NAME="AEN5631" |
0 | 139 ></A |
140 ><H2 | |
141 >Return Value</H2 | |
142 ><P | |
143 >Returns a pointer to the event filter or <TT | |
144 CLASS="LITERAL" | |
145 >NULL</TT | |
146 > if no filter has been set.</P | |
147 ></DIV | |
148 ><DIV | |
149 CLASS="REFSECT1" | |
150 ><A | |
803
355632dca928
Updated SDL HTML documentation
Sam Lantinga <slouken@libsdl.org>
parents:
181
diff
changeset
|
151 NAME="AEN5635" |
0 | 152 ></A |
153 ><H2 | |
154 >See Also</H2 | |
155 ><P | |
156 ><A | |
157 HREF="sdlevent.html" | |
158 ><SPAN | |
159 CLASS="STRUCTNAME" | |
160 >SDL_Event</SPAN | |
161 ></A | |
162 >, | |
163 <A | |
164 HREF="sdlseteventfilter.html" | |
165 ><TT | |
166 CLASS="FUNCTION" | |
167 >SDL_SetEventFilter</TT | |
168 ></A | |
169 ></P | |
170 ></DIV | |
171 ><DIV | |
172 CLASS="NAVFOOTER" | |
173 ><HR | |
174 ALIGN="LEFT" | |
175 WIDTH="100%"><TABLE | |
803
355632dca928
Updated SDL HTML documentation
Sam Lantinga <slouken@libsdl.org>
parents:
181
diff
changeset
|
176 SUMMARY="Footer navigation table" |
0 | 177 WIDTH="100%" |
178 BORDER="0" | |
179 CELLPADDING="0" | |
180 CELLSPACING="0" | |
181 ><TR | |
182 ><TD | |
183 WIDTH="33%" | |
184 ALIGN="left" | |
185 VALIGN="top" | |
186 ><A | |
187 HREF="sdlseteventfilter.html" | |
803
355632dca928
Updated SDL HTML documentation
Sam Lantinga <slouken@libsdl.org>
parents:
181
diff
changeset
|
188 ACCESSKEY="P" |
0 | 189 >Prev</A |
190 ></TD | |
191 ><TD | |
192 WIDTH="34%" | |
193 ALIGN="center" | |
194 VALIGN="top" | |
195 ><A | |
196 HREF="index.html" | |
803
355632dca928
Updated SDL HTML documentation
Sam Lantinga <slouken@libsdl.org>
parents:
181
diff
changeset
|
197 ACCESSKEY="H" |
0 | 198 >Home</A |
199 ></TD | |
200 ><TD | |
201 WIDTH="33%" | |
202 ALIGN="right" | |
203 VALIGN="top" | |
204 ><A | |
205 HREF="sdleventstate.html" | |
803
355632dca928
Updated SDL HTML documentation
Sam Lantinga <slouken@libsdl.org>
parents:
181
diff
changeset
|
206 ACCESSKEY="N" |
0 | 207 >Next</A |
208 ></TD | |
209 ></TR | |
210 ><TR | |
211 ><TD | |
212 WIDTH="33%" | |
213 ALIGN="left" | |
214 VALIGN="top" | |
215 >SDL_SetEventFilter</TD | |
216 ><TD | |
217 WIDTH="34%" | |
218 ALIGN="center" | |
219 VALIGN="top" | |
220 ><A | |
221 HREF="eventfunctions.html" | |
803
355632dca928
Updated SDL HTML documentation
Sam Lantinga <slouken@libsdl.org>
parents:
181
diff
changeset
|
222 ACCESSKEY="U" |
0 | 223 >Up</A |
224 ></TD | |
225 ><TD | |
226 WIDTH="33%" | |
227 ALIGN="right" | |
228 VALIGN="top" | |
229 >SDL_EventState</TD | |
230 ></TR | |
231 ></TABLE | |
232 ></DIV | |
233 ></BODY | |
234 ></HTML | |
235 > |