Mercurial > sdl-ios-xcode
annotate docs/html/sdlresizeevent.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> |
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date | Tue, 17 Feb 2009 05:39:18 +0000 |
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0 | 1 <HTML |
2 ><HEAD | |
3 ><TITLE | |
4 >SDL_ResizeEvent</TITLE | |
5 ><META | |
6 NAME="GENERATOR" | |
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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="SDL Event Structures." | |
14 HREF="eventstructures.html"><LINK | |
15 REL="PREVIOUS" | |
16 TITLE="SDL_JoyBallEvent" | |
17 HREF="sdljoyballevent.html"><LINK | |
18 REL="NEXT" | |
181
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19 TITLE="SDL_ExposeEvent" |
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20 HREF="sdlexposeevent.html"></HEAD |
0 | 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 | |
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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="sdljoyballevent.html" | |
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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 | |
181
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62 HREF="sdlexposeevent.html" |
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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="SDLRESIZEEVENT" | |
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74 ></A |
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75 >SDL_ResizeEvent</H1 |
0 | 76 ><DIV |
77 CLASS="REFNAMEDIV" | |
78 ><A | |
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79 NAME="AEN4453" |
0 | 80 ></A |
81 ><H2 | |
82 >Name</H2 | |
83 >SDL_ResizeEvent -- Window resize event structure</DIV | |
84 ><DIV | |
85 CLASS="REFSECT1" | |
86 ><A | |
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87 NAME="AEN4456" |
0 | 88 ></A |
89 ><H2 | |
90 >Structure Definition</H2 | |
91 ><PRE | |
92 CLASS="PROGRAMLISTING" | |
93 >typedef struct{ | |
94 Uint8 type; | |
95 int w, h; | |
96 } SDL_ResizeEvent;</PRE | |
97 ></DIV | |
98 ><DIV | |
99 CLASS="REFSECT1" | |
100 ><A | |
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101 NAME="AEN4459" |
0 | 102 ></A |
103 ><H2 | |
104 >Structure Data</H2 | |
105 ><DIV | |
106 CLASS="INFORMALTABLE" | |
107 ><A | |
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108 NAME="AEN4461" |
0 | 109 ></A |
110 ><P | |
111 ></P | |
112 ><TABLE | |
113 BORDER="0" | |
114 CLASS="CALSTABLE" | |
115 ><TBODY | |
116 ><TR | |
117 ><TD | |
118 ALIGN="LEFT" | |
119 VALIGN="TOP" | |
120 ><TT | |
121 CLASS="STRUCTFIELD" | |
122 ><I | |
123 >type</I | |
124 ></TT | |
125 ></TD | |
126 ><TD | |
127 ALIGN="LEFT" | |
128 VALIGN="TOP" | |
129 ><TT | |
130 CLASS="LITERAL" | |
131 >SDL_VIDEORESIZE</TT | |
132 ></TD | |
133 ></TR | |
134 ><TR | |
135 ><TD | |
136 ALIGN="LEFT" | |
137 VALIGN="TOP" | |
138 ><TT | |
139 CLASS="STRUCTFIELD" | |
140 ><I | |
141 >w</I | |
142 ></TT | |
143 >, <TT | |
144 CLASS="STRUCTFIELD" | |
145 ><I | |
146 >h</I | |
147 ></TT | |
148 ></TD | |
149 ><TD | |
150 ALIGN="LEFT" | |
151 VALIGN="TOP" | |
152 >New width and height of the window</TD | |
153 ></TR | |
154 ></TBODY | |
155 ></TABLE | |
156 ><P | |
157 ></P | |
158 ></DIV | |
159 ></DIV | |
160 ><DIV | |
161 CLASS="REFSECT1" | |
162 ><A | |
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163 NAME="AEN4474" |
0 | 164 ></A |
165 ><H2 | |
166 >Description</H2 | |
167 ><P | |
168 ><SPAN | |
169 CLASS="STRUCTNAME" | |
170 >SDL_ResizeEvent</SPAN | |
171 > is a member of the <A | |
172 HREF="sdlevent.html" | |
173 ><SPAN | |
174 CLASS="STRUCTNAME" | |
175 >SDL_Event</SPAN | |
176 ></A | |
177 > union and is used when an event of type <TT | |
178 CLASS="LITERAL" | |
179 >SDL_VIDEORESIZE</TT | |
180 > is reported.</P | |
181 ><P | |
182 >When <TT | |
183 CLASS="LITERAL" | |
184 >SDL_RESIZABLE</TT | |
185 > is passed as a <TT | |
186 CLASS="PARAMETER" | |
187 ><I | |
188 >flag</I | |
189 ></TT | |
190 > to <A | |
191 HREF="sdlsetvideomode.html" | |
192 ><TT | |
193 CLASS="FUNCTION" | |
194 >SDL_SetVideoMode</TT | |
195 ></A | |
196 > the user is allowed to resize the applications window. When the window is resized an <TT | |
197 CLASS="LITERAL" | |
198 >SDL_VIDEORESIZE</TT | |
199 > is report, with the new window width and height values stored in <TT | |
200 CLASS="STRUCTFIELD" | |
201 ><I | |
202 >w</I | |
203 ></TT | |
204 > and <TT | |
205 CLASS="STRUCTFIELD" | |
206 ><I | |
207 >h</I | |
208 ></TT | |
209 >, respectively. When an <TT | |
210 CLASS="LITERAL" | |
211 >SDL_VIDEORESIZE</TT | |
212 > is recieved the window should be resized to the new dimensions using <A | |
213 HREF="sdlsetvideomode.html" | |
214 ><TT | |
215 CLASS="FUNCTION" | |
216 >SDL_SetVideoMode</TT | |
217 ></A | |
218 >.</P | |
219 ></DIV | |
220 ><DIV | |
221 CLASS="REFSECT1" | |
222 ><A | |
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223 NAME="AEN4492" |
0 | 224 ></A |
225 ><H2 | |
226 >See Also</H2 | |
227 ><P | |
228 ><A | |
229 HREF="sdlevent.html" | |
230 ><SPAN | |
231 CLASS="STRUCTNAME" | |
232 >SDL_Event</SPAN | |
233 ></A | |
234 >, | |
235 <A | |
236 HREF="sdlsetvideomode.html" | |
237 ><TT | |
238 CLASS="FUNCTION" | |
239 >SDL_SetVideoMode</TT | |
240 ></A | |
241 ></P | |
242 ></DIV | |
243 ><DIV | |
244 CLASS="NAVFOOTER" | |
245 ><HR | |
246 ALIGN="LEFT" | |
247 WIDTH="100%"><TABLE | |
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248 SUMMARY="Footer navigation table" |
0 | 249 WIDTH="100%" |
250 BORDER="0" | |
251 CELLPADDING="0" | |
252 CELLSPACING="0" | |
253 ><TR | |
254 ><TD | |
255 WIDTH="33%" | |
256 ALIGN="left" | |
257 VALIGN="top" | |
258 ><A | |
259 HREF="sdljoyballevent.html" | |
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260 ACCESSKEY="P" |
0 | 261 >Prev</A |
262 ></TD | |
263 ><TD | |
264 WIDTH="34%" | |
265 ALIGN="center" | |
266 VALIGN="top" | |
267 ><A | |
268 HREF="index.html" | |
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269 ACCESSKEY="H" |
0 | 270 >Home</A |
271 ></TD | |
272 ><TD | |
273 WIDTH="33%" | |
274 ALIGN="right" | |
275 VALIGN="top" | |
276 ><A | |
181
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277 HREF="sdlexposeevent.html" |
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278 ACCESSKEY="N" |
0 | 279 >Next</A |
280 ></TD | |
281 ></TR | |
282 ><TR | |
283 ><TD | |
284 WIDTH="33%" | |
285 ALIGN="left" | |
286 VALIGN="top" | |
287 >SDL_JoyBallEvent</TD | |
288 ><TD | |
289 WIDTH="34%" | |
290 ALIGN="center" | |
291 VALIGN="top" | |
292 ><A | |
293 HREF="eventstructures.html" | |
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294 ACCESSKEY="U" |
0 | 295 >Up</A |
296 ></TD | |
297 ><TD | |
298 WIDTH="33%" | |
299 ALIGN="right" | |
300 VALIGN="top" | |
181
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301 >SDL_ExposeEvent</TD |
0 | 302 ></TR |
303 ></TABLE | |
304 ></DIV | |
305 ></BODY | |
306 ></HTML | |
307 > |