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1 """Synchronization metaclass. |
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2 |
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3 This metaclass makes it possible to declare synchronized methods. |
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4 |
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5 """ |
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6 |
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7 import thread |
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8 |
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9 # First we need to define a reentrant lock. |
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10 # This is generally useful and should probably be in a standard Python |
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11 # library module. For now, we in-line it. |
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12 |
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13 class Lock: |
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14 |
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15 """Reentrant lock. |
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16 |
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17 This is a mutex-like object which can be acquired by the same |
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18 thread more than once. It keeps a reference count of the number |
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19 of times it has been acquired by the same thread. Each acquire() |
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20 call must be matched by a release() call and only the last |
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21 release() call actually releases the lock for acquisition by |
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22 another thread. |
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23 |
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24 The implementation uses two locks internally: |
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25 |
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26 __mutex is a short term lock used to protect the instance variables |
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27 __wait is the lock for which other threads wait |
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28 |
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29 A thread intending to acquire both locks should acquire __wait |
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30 first. |
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31 |
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32 The implementation uses two other instance variables, protected by |
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33 locking __mutex: |
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34 |
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35 __tid is the thread ID of the thread that currently has the lock |
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36 __count is the number of times the current thread has acquired it |
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37 |
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38 When the lock is released, __tid is None and __count is zero. |
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39 |
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40 """ |
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41 |
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42 def __init__(self): |
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43 """Constructor. Initialize all instance variables.""" |
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44 self.__mutex = thread.allocate_lock() |
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45 self.__wait = thread.allocate_lock() |
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46 self.__tid = None |
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47 self.__count = 0 |
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48 |
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49 def acquire(self, flag=1): |
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50 """Acquire the lock. |
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51 |
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52 If the optional flag argument is false, returns immediately |
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53 when it cannot acquire the __wait lock without blocking (it |
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54 may still block for a little while in order to acquire the |
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55 __mutex lock). |
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56 |
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57 The return value is only relevant when the flag argument is |
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58 false; it is 1 if the lock is acquired, 0 if not. |
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59 |
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60 """ |
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61 self.__mutex.acquire() |
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62 try: |
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63 if self.__tid == thread.get_ident(): |
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64 self.__count = self.__count + 1 |
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65 return 1 |
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66 finally: |
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67 self.__mutex.release() |
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68 locked = self.__wait.acquire(flag) |
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69 if not flag and not locked: |
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70 return 0 |
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71 try: |
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72 self.__mutex.acquire() |
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73 assert self.__tid == None |
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74 assert self.__count == 0 |
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75 self.__tid = thread.get_ident() |
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76 self.__count = 1 |
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77 return 1 |
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78 finally: |
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79 self.__mutex.release() |
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80 |
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81 def release(self): |
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82 """Release the lock. |
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83 |
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84 If this thread doesn't currently have the lock, an assertion |
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85 error is raised. |
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86 |
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87 Only allow another thread to acquire the lock when the count |
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88 reaches zero after decrementing it. |
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89 |
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90 """ |
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91 self.__mutex.acquire() |
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92 try: |
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93 assert self.__tid == thread.get_ident() |
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94 assert self.__count > 0 |
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95 self.__count = self.__count - 1 |
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96 if self.__count == 0: |
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97 self.__tid = None |
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98 self.__wait.release() |
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99 finally: |
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100 self.__mutex.release() |
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101 |
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102 |
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103 def _testLock(): |
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104 |
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105 done = [] |
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106 |
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107 def f2(lock, done=done): |
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108 lock.acquire() |
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109 print "f2 running in thread %d\n" % thread.get_ident(), |
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110 lock.release() |
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111 done.append(1) |
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112 |
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113 def f1(lock, f2=f2, done=done): |
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114 lock.acquire() |
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115 print "f1 running in thread %d\n" % thread.get_ident(), |
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116 try: |
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117 f2(lock) |
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118 finally: |
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119 lock.release() |
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120 done.append(1) |
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121 |
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122 lock = Lock() |
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123 lock.acquire() |
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124 f1(lock) # Adds 2 to done |
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125 lock.release() |
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126 |
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127 lock.acquire() |
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128 |
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129 thread.start_new_thread(f1, (lock,)) # Adds 2 |
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130 thread.start_new_thread(f1, (lock, f1)) # Adds 3 |
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131 thread.start_new_thread(f2, (lock,)) # Adds 1 |
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132 thread.start_new_thread(f2, (lock,)) # Adds 1 |
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133 |
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134 lock.release() |
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135 import time |
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136 while len(done) < 9: |
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137 print len(done) |
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138 time.sleep(0.001) |
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139 print len(done) |
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140 |
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141 |
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142 # Now, the Locking metaclass is a piece of cake. |
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143 # As an example feature, methods whose name begins with exactly one |
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144 # underscore are not synchronized. |
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145 |
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146 from Meta import MetaClass, MetaHelper, MetaMethodWrapper |
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147 |
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148 class LockingMethodWrapper(MetaMethodWrapper): |
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149 def __call__(self, *args, **kw): |
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150 if self.__name__[:1] == '_' and self.__name__[1:] != '_': |
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151 return apply(self.func, (self.inst,) + args, kw) |
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152 self.inst.__lock__.acquire() |
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153 try: |
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154 return apply(self.func, (self.inst,) + args, kw) |
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155 finally: |
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156 self.inst.__lock__.release() |
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157 |
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158 class LockingHelper(MetaHelper): |
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159 __methodwrapper__ = LockingMethodWrapper |
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160 def __helperinit__(self, formalclass): |
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161 MetaHelper.__helperinit__(self, formalclass) |
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162 self.__lock__ = Lock() |
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163 |
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164 class LockingMetaClass(MetaClass): |
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165 __helper__ = LockingHelper |
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166 |
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167 Locking = LockingMetaClass('Locking', (), {}) |
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168 |
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169 def _test(): |
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170 # For kicks, take away the Locking base class and see it die |
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171 class Buffer(Locking): |
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172 def __init__(self, initialsize): |
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173 assert initialsize > 0 |
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174 self.size = initialsize |
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175 self.buffer = [None]*self.size |
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176 self.first = self.last = 0 |
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177 def put(self, item): |
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178 # Do we need to grow the buffer? |
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179 if (self.last+1) % self.size != self.first: |
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180 # Insert the new item |
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181 self.buffer[self.last] = item |
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182 self.last = (self.last+1) % self.size |
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183 return |
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184 # Double the buffer size |
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185 # First normalize it so that first==0 and last==size-1 |
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186 print "buffer =", self.buffer |
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187 print "first = %d, last = %d, size = %d" % ( |
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188 self.first, self.last, self.size) |
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189 if self.first <= self.last: |
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190 temp = self.buffer[self.first:self.last] |
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191 else: |
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192 temp = self.buffer[self.first:] + self.buffer[:self.last] |
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193 print "temp =", temp |
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194 self.buffer = temp + [None]*(self.size+1) |
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195 self.first = 0 |
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196 self.last = self.size-1 |
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197 self.size = self.size*2 |
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198 print "Buffer size doubled to", self.size |
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199 print "new buffer =", self.buffer |
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200 print "first = %d, last = %d, size = %d" % ( |
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201 self.first, self.last, self.size) |
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202 self.put(item) # Recursive call to test the locking |
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203 def get(self): |
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204 # Is the buffer empty? |
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205 if self.first == self.last: |
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206 raise EOFError # Avoid defining a new exception |
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207 item = self.buffer[self.first] |
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208 self.first = (self.first+1) % self.size |
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209 return item |
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210 |
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211 def producer(buffer, wait, n=1000): |
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212 import time |
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213 i = 0 |
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214 while i < n: |
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215 print "put", i |
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216 buffer.put(i) |
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217 i = i+1 |
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218 print "Producer: done producing", n, "items" |
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219 wait.release() |
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220 |
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221 def consumer(buffer, wait, n=1000): |
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222 import time |
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223 i = 0 |
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224 tout = 0.001 |
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225 while i < n: |
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226 try: |
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227 x = buffer.get() |
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228 if x != i: |
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229 raise AssertionError, \ |
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230 "get() returned %s, expected %s" % (x, i) |
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231 print "got", i |
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232 i = i+1 |
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233 tout = 0.001 |
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234 except EOFError: |
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235 time.sleep(tout) |
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236 tout = tout*2 |
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237 print "Consumer: done consuming", n, "items" |
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238 wait.release() |
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239 |
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240 pwait = thread.allocate_lock() |
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241 pwait.acquire() |
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242 cwait = thread.allocate_lock() |
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243 cwait.acquire() |
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244 buffer = Buffer(1) |
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245 n = 1000 |
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246 thread.start_new_thread(consumer, (buffer, cwait, n)) |
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247 thread.start_new_thread(producer, (buffer, pwait, n)) |
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248 pwait.acquire() |
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249 print "Producer done" |
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250 cwait.acquire() |
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251 print "All done" |
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252 print "buffer size ==", len(buffer.buffer) |
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253 |
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254 if __name__ == '__main__': |
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255 _testLock() |
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256 _test() |