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annotate src/thread/win32/win_ce_semaphore.c @ 626:b98f732b4322

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*** empty log message ***
author Sam Lantinga <slouken@libsdl.org>
date Thu, 29 May 2003 04:23:03 +0000
parents 13ee9f4834ea
children 86d0d01290ea
rev   line source
36
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1 /* win_ce_semaphore.c
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2
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3 Copyright (c) 1998, Johnson M. Hart
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4 (with corrections 2001 by Rainer Loritz)
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5 Permission is granted for any and all use providing that this
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6 copyright is properly acknowledged.
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7 There are no assurances of suitability for any use whatsoever.
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8
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9 WINDOWS CE: There is a collection of Windows CE functions to simulate
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10 semaphores using only a mutex and an event. As Windows CE events cannot
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11 be named, these simulated semaphores cannot be named either.
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12
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13 Implementation notes:
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14 1. All required internal data structures are allocated on the process's heap.
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15 2. Where appropriate, a new error code is returned (see the header
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16 file), or, if the error is a Win32 error, that code is unchanged.
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17 3. Notice the new handle type "SYNCHHANDLE" that has handles, counters,
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18 and other information. This structure will grow as new objects are added
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19 to this set; some members are specific to only one or two of the objects.
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20 4. Mutexes are used for critical sections. These could be replaced with
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21 CRITICAL_SECTION objects but then this would give up the time out
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22 capability.
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23 5. The implementation shows several interesting aspects of synchronization, some
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24 of which are specific to Win32 and some of which are general. These are pointed
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25 out in the comments as appropriate.
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26 6. The wait function emulates WaitForSingleObject only. An emulation of
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27 WaitForMultipleObjects is much harder to implement outside the kernel,
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28 and it is not clear how to handle a mixture of WCE semaphores and normal
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29 events and mutexes. */
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30
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31 #include <windows.h>
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32 #include "win_ce_semaphore.h"
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33
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34 static SYNCHHANDLE CleanUp (SYNCHHANDLE hSynch, DWORD Flags);
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35
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36 SYNCHHANDLE CreateSemaphoreCE (
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37
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38 LPSECURITY_ATTRIBUTES lpSemaphoreAttributes, /* pointer to security attributes */
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39 LONG lInitialCount, /* initial count */
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40 LONG lMaximumCount, /* maximum count */
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41 LPCTSTR lpName )
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42
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43 /* Semaphore for use with Windows CE that does not support them directly.
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44 Requires a counter, a mutex to protect the counter, and an
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45 autoreset event.
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46
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47 Here are the rules that must always hold between the autoreset event
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48 and the mutex (any violation of these rules by the CE semaphore functions
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49 will, in all likelihood, result in a defect):
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50 1. No thread can set, pulse, or reset the event,
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51 nor can it access any part of the SYNCHHANDLE structure,
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52 without first gaining ownership of the mutex.
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53 BUT, a thread can wait on the event without owning the mutex
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54 (this is clearly necessary or else the event could never be set).
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55 2. The event is in a signaled state if and only if the current semaphore
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56 count ("CurCount") is greater than zero.
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57 3. The semaphore count is always >= 0 and <= the maximum count */
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58
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59 {
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60 SYNCHHANDLE hSynch = NULL, result = NULL;
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61
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62 __try
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63 {
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64 if (lInitialCount > lMaximumCount || lMaximumCount < 0 || lInitialCount < 0)
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65 {
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66 /* Bad parameters */
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67 SetLastError (SYNCH_ERROR);
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68 __leave;
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69 }
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70
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71 hSynch = HeapAlloc (GetProcessHeap(), HEAP_ZERO_MEMORY, SYNCH_HANDLE_SIZE);
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72 if (hSynch == NULL) __leave;
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73
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74 hSynch->MaxCount = lMaximumCount;
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75 hSynch->CurCount = lInitialCount;
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76 hSynch->lpName = lpName;
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77
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78 hSynch->hMutex = CreateMutex (lpSemaphoreAttributes, FALSE, NULL);
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79
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80 WaitForSingleObject (hSynch->hMutex, INFINITE);
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81 /* Create the event. It is initially signaled if and only if the
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82 initial count is > 0 */
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83 hSynch->hEvent = CreateEvent (lpSemaphoreAttributes, FALSE,
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84 lInitialCount > 0, NULL);
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85 ReleaseMutex (hSynch->hMutex);
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86 hSynch->hSemph = NULL;
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87 }
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88 __finally
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89 {
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90 /* Return with the handle, or, if there was any error, return
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91 a null after closing any open handles and freeing any allocated memory. */
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92 result=CleanUp(hSynch, 6 /* An event and a mutex, but no semaphore. */);
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93 }
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94
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95 return result;
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96 }
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97
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98 BOOL ReleaseSemaphoreCE (SYNCHHANDLE hSemCE, LONG cReleaseCount, LPLONG lpPreviousCount)
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99 /* Windows CE equivalent to ReleaseSemaphore. */
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100 {
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101 BOOL Result = TRUE;
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102
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103 /* Gain access to the object to assure that the release count
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104 would not cause the total count to exceed the maximum. */
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105
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106 __try
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107 {
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108 WaitForSingleObject (hSemCE->hMutex, INFINITE);
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109 /* reply only if asked to */
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110 if (lpPreviousCount!=NULL)
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111 *lpPreviousCount = hSemCE->CurCount;
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112 if (hSemCE->CurCount + cReleaseCount > hSemCE->MaxCount || cReleaseCount <= 0)
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113 {
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114 SetLastError (SYNCH_ERROR);
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115 Result = FALSE;
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116 __leave;
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117 }
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118 hSemCE->CurCount += cReleaseCount;
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119
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120 /* Set the autoreset event, releasing exactly one waiting thread, now or
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121 in the future. */
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122
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123 SetEvent (hSemCE->hEvent);
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124 }
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125 __finally
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126 {
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127 ReleaseMutex (hSemCE->hMutex);
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128 }
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129
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130 return Result;
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131 }
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132
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133 DWORD WaitForSemaphoreCE (SYNCHHANDLE hSemCE, DWORD dwMilliseconds)
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134 /* Windows CE semaphore equivalent of WaitForSingleObject. */
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135 {
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136 DWORD WaitResult;
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137
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138 WaitResult = WaitForSingleObject (hSemCE->hMutex, dwMilliseconds);
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139 if (WaitResult != WAIT_OBJECT_0 && WaitResult != WAIT_ABANDONED_0) return WaitResult;
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140 while (hSemCE->CurCount <= 0)
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141 {
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142
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143 /* The count is 0, and the thread must wait on the event (which, by
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144 the rules, is currently reset) for semaphore resources to become
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145 available. First, of course, the mutex must be released so that another
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146 thread will be capable of setting the event. */
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147
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148 ReleaseMutex (hSemCE->hMutex);
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149
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150 /* Wait for the event to be signaled, indicating a semaphore state change.
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151 The event is autoreset and signaled with a SetEvent (not PulseEvent)
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152 so exactly one waiting thread (whether or not there is currently
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153 a waiting thread) is released as a result of the SetEvent. */
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154
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155 WaitResult = WaitForSingleObject (hSemCE->hEvent, dwMilliseconds);
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156 if (WaitResult != WAIT_OBJECT_0) return WaitResult;
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157
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158 /* This is where the properties of setting of an autoreset event is critical
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159 to assure that, even if the semaphore state changes between the
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160 preceding Wait and the next, and even if NO threads are waiting
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161 on the event at the time of the SetEvent, at least one thread
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162 will be released.
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163 Pulsing a manual reset event would appear to work, but it would have
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164 a defect which could appear if the semaphore state changed between
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165 the two waits. */
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166
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167 WaitResult = WaitForSingleObject (hSemCE->hMutex, dwMilliseconds);
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168 if (WaitResult != WAIT_OBJECT_0 && WaitResult != WAIT_ABANDONED_0) return WaitResult;
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169
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170 }
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171 /* The count is not zero and this thread owns the mutex. */
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172
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173 hSemCE->CurCount--;
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174 /* The event is now unsignaled, BUT, the semaphore count may not be
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175 zero, in which case the event should be signaled again
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176 before releasing the mutex. */
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177
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178 if (hSemCE->CurCount > 0) SetEvent (hSemCE->hEvent);
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179 ReleaseMutex (hSemCE->hMutex);
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180 return WaitResult;
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181 }
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182
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183 BOOL CloseSynchHandle (SYNCHHANDLE hSynch)
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184 /* Close a synchronization handle.
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185 Improvement: Test for a valid handle before dereferencing the handle. */
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186 {
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187 BOOL Result = TRUE;
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188 if (hSynch->hEvent != NULL) Result = Result && CloseHandle (hSynch->hEvent);
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189 if (hSynch->hMutex != NULL) Result = Result && CloseHandle (hSynch->hMutex);
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190 if (hSynch->hSemph != NULL) Result = Result && CloseHandle (hSynch->hSemph);
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191 HeapFree (GetProcessHeap (), 0, hSynch);
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192 return (Result);
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193 }
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194
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195 static SYNCHHANDLE CleanUp (SYNCHHANDLE hSynch, DWORD Flags)
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196 { /* Prepare to return from a create of a synchronization handle.
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197 If there was any failure, free any allocated resources.
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198 "Flags" indicates which Win32 objects are required in the
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199 synchronization handle. */
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200
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201 BOOL ok = TRUE;
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202
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203 if (hSynch == NULL) return NULL;
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204 if (Flags & 4 == 1 && hSynch->hEvent == NULL) ok = FALSE;
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205 if (Flags & 2 == 1 && hSynch->hMutex == NULL) ok = FALSE;
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206 if (Flags & 1 == 1 && hSynch->hEvent == NULL) ok = FALSE;
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207 if (!ok)
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208 {
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209 CloseSynchHandle (hSynch);
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210 return NULL;
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211 }
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212 /* Everything worked */
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213 return hSynch;
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214 }