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comparison src/thread/win32/win_ce_semaphore.c @ 36:13ee9f4834ea

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Windows CE patches contributed by Rainer Loritz
author Sam Lantinga <slouken@lokigames.com>
date Wed, 23 May 2001 23:35:10 +0000
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children 86d0d01290ea
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35:d3bc792e136d 36:13ee9f4834ea
1 /* win_ce_semaphore.c
2
3 Copyright (c) 1998, Johnson M. Hart
4 (with corrections 2001 by Rainer Loritz)
5 Permission is granted for any and all use providing that this
6 copyright is properly acknowledged.
7 There are no assurances of suitability for any use whatsoever.
8
9 WINDOWS CE: There is a collection of Windows CE functions to simulate
10 semaphores using only a mutex and an event. As Windows CE events cannot
11 be named, these simulated semaphores cannot be named either.
12
13 Implementation notes:
14 1. All required internal data structures are allocated on the process's heap.
15 2. Where appropriate, a new error code is returned (see the header
16 file), or, if the error is a Win32 error, that code is unchanged.
17 3. Notice the new handle type "SYNCHHANDLE" that has handles, counters,
18 and other information. This structure will grow as new objects are added
19 to this set; some members are specific to only one or two of the objects.
20 4. Mutexes are used for critical sections. These could be replaced with
21 CRITICAL_SECTION objects but then this would give up the time out
22 capability.
23 5. The implementation shows several interesting aspects of synchronization, some
24 of which are specific to Win32 and some of which are general. These are pointed
25 out in the comments as appropriate.
26 6. The wait function emulates WaitForSingleObject only. An emulation of
27 WaitForMultipleObjects is much harder to implement outside the kernel,
28 and it is not clear how to handle a mixture of WCE semaphores and normal
29 events and mutexes. */
30
31 #include <windows.h>
32 #include "win_ce_semaphore.h"
33
34 static SYNCHHANDLE CleanUp (SYNCHHANDLE hSynch, DWORD Flags);
35
36 SYNCHHANDLE CreateSemaphoreCE (
37
38 LPSECURITY_ATTRIBUTES lpSemaphoreAttributes, /* pointer to security attributes */
39 LONG lInitialCount, /* initial count */
40 LONG lMaximumCount, /* maximum count */
41 LPCTSTR lpName )
42
43 /* Semaphore for use with Windows CE that does not support them directly.
44 Requires a counter, a mutex to protect the counter, and an
45 autoreset event.
46
47 Here are the rules that must always hold between the autoreset event
48 and the mutex (any violation of these rules by the CE semaphore functions
49 will, in all likelihood, result in a defect):
50 1. No thread can set, pulse, or reset the event,
51 nor can it access any part of the SYNCHHANDLE structure,
52 without first gaining ownership of the mutex.
53 BUT, a thread can wait on the event without owning the mutex
54 (this is clearly necessary or else the event could never be set).
55 2. The event is in a signaled state if and only if the current semaphore
56 count ("CurCount") is greater than zero.
57 3. The semaphore count is always >= 0 and <= the maximum count */
58
59 {
60 SYNCHHANDLE hSynch = NULL, result = NULL;
61
62 __try
63 {
64 if (lInitialCount > lMaximumCount || lMaximumCount < 0 || lInitialCount < 0)
65 {
66 /* Bad parameters */
67 SetLastError (SYNCH_ERROR);
68 __leave;
69 }
70
71 hSynch = HeapAlloc (GetProcessHeap(), HEAP_ZERO_MEMORY, SYNCH_HANDLE_SIZE);
72 if (hSynch == NULL) __leave;
73
74 hSynch->MaxCount = lMaximumCount;
75 hSynch->CurCount = lInitialCount;
76 hSynch->lpName = lpName;
77
78 hSynch->hMutex = CreateMutex (lpSemaphoreAttributes, FALSE, NULL);
79
80 WaitForSingleObject (hSynch->hMutex, INFINITE);
81 /* Create the event. It is initially signaled if and only if the
82 initial count is > 0 */
83 hSynch->hEvent = CreateEvent (lpSemaphoreAttributes, FALSE,
84 lInitialCount > 0, NULL);
85 ReleaseMutex (hSynch->hMutex);
86 hSynch->hSemph = NULL;
87 }
88 __finally
89 {
90 /* Return with the handle, or, if there was any error, return
91 a null after closing any open handles and freeing any allocated memory. */
92 result=CleanUp(hSynch, 6 /* An event and a mutex, but no semaphore. */);
93 }
94
95 return result;
96 }
97
98 BOOL ReleaseSemaphoreCE (SYNCHHANDLE hSemCE, LONG cReleaseCount, LPLONG lpPreviousCount)
99 /* Windows CE equivalent to ReleaseSemaphore. */
100 {
101 BOOL Result = TRUE;
102
103 /* Gain access to the object to assure that the release count
104 would not cause the total count to exceed the maximum. */
105
106 __try
107 {
108 WaitForSingleObject (hSemCE->hMutex, INFINITE);
109 /* reply only if asked to */
110 if (lpPreviousCount!=NULL)
111 *lpPreviousCount = hSemCE->CurCount;
112 if (hSemCE->CurCount + cReleaseCount > hSemCE->MaxCount || cReleaseCount <= 0)
113 {
114 SetLastError (SYNCH_ERROR);
115 Result = FALSE;
116 __leave;
117 }
118 hSemCE->CurCount += cReleaseCount;
119
120 /* Set the autoreset event, releasing exactly one waiting thread, now or
121 in the future. */
122
123 SetEvent (hSemCE->hEvent);
124 }
125 __finally
126 {
127 ReleaseMutex (hSemCE->hMutex);
128 }
129
130 return Result;
131 }
132
133 DWORD WaitForSemaphoreCE (SYNCHHANDLE hSemCE, DWORD dwMilliseconds)
134 /* Windows CE semaphore equivalent of WaitForSingleObject. */
135 {
136 DWORD WaitResult;
137
138 WaitResult = WaitForSingleObject (hSemCE->hMutex, dwMilliseconds);
139 if (WaitResult != WAIT_OBJECT_0 && WaitResult != WAIT_ABANDONED_0) return WaitResult;
140 while (hSemCE->CurCount <= 0)
141 {
142
143 /* The count is 0, and the thread must wait on the event (which, by
144 the rules, is currently reset) for semaphore resources to become
145 available. First, of course, the mutex must be released so that another
146 thread will be capable of setting the event. */
147
148 ReleaseMutex (hSemCE->hMutex);
149
150 /* Wait for the event to be signaled, indicating a semaphore state change.
151 The event is autoreset and signaled with a SetEvent (not PulseEvent)
152 so exactly one waiting thread (whether or not there is currently
153 a waiting thread) is released as a result of the SetEvent. */
154
155 WaitResult = WaitForSingleObject (hSemCE->hEvent, dwMilliseconds);
156 if (WaitResult != WAIT_OBJECT_0) return WaitResult;
157
158 /* This is where the properties of setting of an autoreset event is critical
159 to assure that, even if the semaphore state changes between the
160 preceding Wait and the next, and even if NO threads are waiting
161 on the event at the time of the SetEvent, at least one thread
162 will be released.
163 Pulsing a manual reset event would appear to work, but it would have
164 a defect which could appear if the semaphore state changed between
165 the two waits. */
166
167 WaitResult = WaitForSingleObject (hSemCE->hMutex, dwMilliseconds);
168 if (WaitResult != WAIT_OBJECT_0 && WaitResult != WAIT_ABANDONED_0) return WaitResult;
169
170 }
171 /* The count is not zero and this thread owns the mutex. */
172
173 hSemCE->CurCount--;
174 /* The event is now unsignaled, BUT, the semaphore count may not be
175 zero, in which case the event should be signaled again
176 before releasing the mutex. */
177
178 if (hSemCE->CurCount > 0) SetEvent (hSemCE->hEvent);
179 ReleaseMutex (hSemCE->hMutex);
180 return WaitResult;
181 }
182
183 BOOL CloseSynchHandle (SYNCHHANDLE hSynch)
184 /* Close a synchronization handle.
185 Improvement: Test for a valid handle before dereferencing the handle. */
186 {
187 BOOL Result = TRUE;
188 if (hSynch->hEvent != NULL) Result = Result && CloseHandle (hSynch->hEvent);
189 if (hSynch->hMutex != NULL) Result = Result && CloseHandle (hSynch->hMutex);
190 if (hSynch->hSemph != NULL) Result = Result && CloseHandle (hSynch->hSemph);
191 HeapFree (GetProcessHeap (), 0, hSynch);
192 return (Result);
193 }
194
195 static SYNCHHANDLE CleanUp (SYNCHHANDLE hSynch, DWORD Flags)
196 { /* Prepare to return from a create of a synchronization handle.
197 If there was any failure, free any allocated resources.
198 "Flags" indicates which Win32 objects are required in the
199 synchronization handle. */
200
201 BOOL ok = TRUE;
202
203 if (hSynch == NULL) return NULL;
204 if (Flags & 4 == 1 && hSynch->hEvent == NULL) ok = FALSE;
205 if (Flags & 2 == 1 && hSynch->hMutex == NULL) ok = FALSE;
206 if (Flags & 1 == 1 && hSynch->hEvent == NULL) ok = FALSE;
207 if (!ok)
208 {
209 CloseSynchHandle (hSynch);
210 return NULL;
211 }
212 /* Everything worked */
213 return hSynch;
214 }