Mercurial > sdl-ios-xcode
annotate docs/html/sdlmousebuttonevent.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_MouseButtonEvent</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_MouseMotionEvent" | |
17 HREF="sdlmousemotionevent.html"><LINK | |
18 REL="NEXT" | |
19 TITLE="SDL_JoyAxisEvent" | |
20 HREF="sdljoyaxisevent.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 | |
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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="sdlmousemotionevent.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 | |
62 HREF="sdljoyaxisevent.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="SDLMOUSEBUTTONEVENT" | |
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74 ></A |
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75 >SDL_MouseButtonEvent</H1 |
0 | 76 ><DIV |
77 CLASS="REFNAMEDIV" | |
78 ><A | |
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79 NAME="AEN4144" |
0 | 80 ></A |
81 ><H2 | |
82 >Name</H2 | |
83 >SDL_MouseButtonEvent -- Mouse button event structure</DIV | |
84 ><DIV | |
85 CLASS="REFSECT1" | |
86 ><A | |
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87 NAME="AEN4147" |
0 | 88 ></A |
89 ><H2 | |
90 >Structure Definition</H2 | |
91 ><PRE | |
92 CLASS="PROGRAMLISTING" | |
93 >typedef struct{ | |
94 Uint8 type; | |
95 Uint8 button; | |
96 Uint8 state; | |
97 Uint16 x, y; | |
98 } SDL_MouseButtonEvent;</PRE | |
99 ></DIV | |
100 ><DIV | |
101 CLASS="REFSECT1" | |
102 ><A | |
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103 NAME="AEN4150" |
0 | 104 ></A |
105 ><H2 | |
106 >Structure Data</H2 | |
107 ><DIV | |
108 CLASS="INFORMALTABLE" | |
109 ><A | |
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110 NAME="AEN4152" |
0 | 111 ></A |
112 ><P | |
113 ></P | |
114 ><TABLE | |
115 BORDER="0" | |
116 CLASS="CALSTABLE" | |
117 ><TBODY | |
118 ><TR | |
119 ><TD | |
120 ALIGN="LEFT" | |
121 VALIGN="TOP" | |
122 ><TT | |
123 CLASS="STRUCTFIELD" | |
124 ><I | |
125 >type</I | |
126 ></TT | |
127 ></TD | |
128 ><TD | |
129 ALIGN="LEFT" | |
130 VALIGN="TOP" | |
131 ><TT | |
132 CLASS="LITERAL" | |
133 >SDL_MOUSEBUTTONDOWN</TT | |
134 > or <TT | |
135 CLASS="LITERAL" | |
136 >SDL_MOUSEBUTTONUP</TT | |
137 ></TD | |
138 ></TR | |
139 ><TR | |
140 ><TD | |
141 ALIGN="LEFT" | |
142 VALIGN="TOP" | |
143 ><TT | |
144 CLASS="STRUCTFIELD" | |
145 ><I | |
146 >button</I | |
147 ></TT | |
148 ></TD | |
149 ><TD | |
150 ALIGN="LEFT" | |
151 VALIGN="TOP" | |
152 >The mouse button index (SDL_BUTTON_LEFT, SDL_BUTTON_MIDDLE, SDL_BUTTON_RIGHT)</TD | |
153 ></TR | |
154 ><TR | |
155 ><TD | |
156 ALIGN="LEFT" | |
157 VALIGN="TOP" | |
158 ><TT | |
159 CLASS="STRUCTFIELD" | |
160 ><I | |
161 >state</I | |
162 ></TT | |
163 ></TD | |
164 ><TD | |
165 ALIGN="LEFT" | |
166 VALIGN="TOP" | |
167 ><TT | |
168 CLASS="LITERAL" | |
169 >SDL_PRESSED</TT | |
170 > or <TT | |
171 CLASS="LITERAL" | |
172 >SDL_RELEASED</TT | |
173 ></TD | |
174 ></TR | |
175 ><TR | |
176 ><TD | |
177 ALIGN="LEFT" | |
178 VALIGN="TOP" | |
179 ><TT | |
180 CLASS="STRUCTFIELD" | |
181 ><I | |
182 >x</I | |
183 ></TT | |
184 >, <TT | |
185 CLASS="STRUCTFIELD" | |
186 ><I | |
187 >y</I | |
188 ></TT | |
189 ></TD | |
190 ><TD | |
191 ALIGN="LEFT" | |
192 VALIGN="TOP" | |
193 >The X/Y coordinates of the mouse at press/release time</TD | |
194 ></TR | |
195 ></TBODY | |
196 ></TABLE | |
197 ><P | |
198 ></P | |
199 ></DIV | |
200 ></DIV | |
201 ><DIV | |
202 CLASS="REFSECT1" | |
203 ><A | |
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204 NAME="AEN4176" |
0 | 205 ></A |
206 ><H2 | |
207 >Description</H2 | |
208 ><P | |
209 ><SPAN | |
210 CLASS="STRUCTNAME" | |
211 >SDL_MouseButtonEvent</SPAN | |
212 > is a member of the <A | |
213 HREF="sdlevent.html" | |
214 ><SPAN | |
215 CLASS="STRUCTNAME" | |
216 >SDL_Event</SPAN | |
217 ></A | |
218 > union and is used when an event of type <TT | |
219 CLASS="LITERAL" | |
220 >SDL_MOUSEBUTTONDOWN</TT | |
221 > or <TT | |
222 CLASS="LITERAL" | |
223 >SDL_MOUSEBUTTONUP</TT | |
224 > is reported.</P | |
225 ><P | |
226 >When a mouse button press or release is detected then number of the button pressed (from 1 to 255, with 1 usually being the left button and 2 the right) is placed into <TT | |
227 CLASS="STRUCTFIELD" | |
228 ><I | |
229 >button</I | |
230 ></TT | |
231 >, the position of the mouse when this event occured is stored in the <TT | |
232 CLASS="STRUCTFIELD" | |
233 ><I | |
234 >x</I | |
235 ></TT | |
236 > and the <TT | |
237 CLASS="STRUCTFIELD" | |
238 ><I | |
239 >y</I | |
240 ></TT | |
241 > fields. Like <A | |
242 HREF="sdlkeyboardevent.html" | |
243 ><SPAN | |
244 CLASS="STRUCTNAME" | |
245 >SDL_KeyboardEvent</SPAN | |
246 ></A | |
247 >, information on whether the event was a press or a release event is stored in both the <TT | |
248 CLASS="STRUCTFIELD" | |
249 ><I | |
250 >type</I | |
251 ></TT | |
252 > and <TT | |
253 CLASS="STRUCTFIELD" | |
254 ><I | |
255 >state</I | |
256 ></TT | |
257 > fields, but this should be obvious.</P | |
258 ></DIV | |
259 ><DIV | |
260 CLASS="REFSECT1" | |
261 ><A | |
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262 NAME="AEN4192" |
0 | 263 ></A |
264 ><H2 | |
265 >See Also</H2 | |
266 ><P | |
267 ><A | |
268 HREF="sdlevent.html" | |
269 ><SPAN | |
270 CLASS="STRUCTNAME" | |
271 >SDL_Event</SPAN | |
272 ></A | |
273 >, | |
274 <A | |
275 HREF="sdlmousemotionevent.html" | |
276 ><SPAN | |
277 CLASS="STRUCTNAME" | |
278 >SDL_MouseMotionEvent</SPAN | |
279 ></A | |
280 ></P | |
281 ></DIV | |
282 ><DIV | |
283 CLASS="NAVFOOTER" | |
284 ><HR | |
285 ALIGN="LEFT" | |
286 WIDTH="100%"><TABLE | |
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287 SUMMARY="Footer navigation table" |
0 | 288 WIDTH="100%" |
289 BORDER="0" | |
290 CELLPADDING="0" | |
291 CELLSPACING="0" | |
292 ><TR | |
293 ><TD | |
294 WIDTH="33%" | |
295 ALIGN="left" | |
296 VALIGN="top" | |
297 ><A | |
298 HREF="sdlmousemotionevent.html" | |
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299 ACCESSKEY="P" |
0 | 300 >Prev</A |
301 ></TD | |
302 ><TD | |
303 WIDTH="34%" | |
304 ALIGN="center" | |
305 VALIGN="top" | |
306 ><A | |
307 HREF="index.html" | |
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308 ACCESSKEY="H" |
0 | 309 >Home</A |
310 ></TD | |
311 ><TD | |
312 WIDTH="33%" | |
313 ALIGN="right" | |
314 VALIGN="top" | |
315 ><A | |
316 HREF="sdljoyaxisevent.html" | |
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317 ACCESSKEY="N" |
0 | 318 >Next</A |
319 ></TD | |
320 ></TR | |
321 ><TR | |
322 ><TD | |
323 WIDTH="33%" | |
324 ALIGN="left" | |
325 VALIGN="top" | |
326 >SDL_MouseMotionEvent</TD | |
327 ><TD | |
328 WIDTH="34%" | |
329 ALIGN="center" | |
330 VALIGN="top" | |
331 ><A | |
332 HREF="eventstructures.html" | |
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333 ACCESSKEY="U" |
0 | 334 >Up</A |
335 ></TD | |
336 ><TD | |
337 WIDTH="33%" | |
338 ALIGN="right" | |
339 VALIGN="top" | |
340 >SDL_JoyAxisEvent</TD | |
341 ></TR | |
342 ></TABLE | |
343 ></DIV | |
344 ></BODY | |
345 ></HTML | |
346 > |