1 | """Easy to use object-oriented thread pool framework. |
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2 | |
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3 | A thread pool is an object that maintains a pool of worker threads to perform |
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4 | time consuming operations in parallel. It assigns jobs to the threads |
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5 | by putting them in a work request queue, where they are picked up by the |
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6 | next available thread. This then performs the requested operation in the |
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7 | background and puts the results in a another queue. |
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8 | |
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9 | The thread pool object can then collect the results from all threads from |
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10 | this queue as soon as they become available or after all threads have |
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11 | finished their work. It's also possible, to define callbacks to handle |
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12 | each result as it comes in. |
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13 | |
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14 | The basic concept and some code was taken from the book "Python in a Nutshell" |
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15 | by Alex Martelli, copyright 2003, ISBN 0-596-00188-6, from section 14.5 |
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16 | "Threaded Program Architecture". I wrapped the main program logic in the |
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17 | ThreadPool class, added the WorkRequest class and the callback system and |
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18 | tweaked the code here and there. Kudos also to Florent Aide for the exception |
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19 | handling mechanism. |
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20 | |
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21 | Basic usage: |
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22 | |
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23 | >>> pool = TreadPool(poolsize) |
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24 | >>> requests = makeRequests(some_callable, list_of_args, callback) |
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25 | >>> [pool.putRequest(req) for req in requests] |
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26 | >>> pool.wait() |
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27 | |
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28 | See the end of the module code for a brief, annotated usage example. |
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29 | |
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30 | Website : http://chrisarndt.de/en/software/python/threadpool/ |
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31 | """ |
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32 | |
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33 | __all__ = [ |
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34 | 'makeRequests', |
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35 | 'NoResultsPending', |
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36 | 'NoWorkersAvailable', |
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37 | 'ThreadPool', |
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38 | 'WorkRequest', |
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39 | 'WorkerThread' |
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40 | ] |
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41 | |
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42 | __author__ = "Christopher Arndt" |
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43 | __version__ = "1.2.3" |
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44 | __revision__ = "$Revision: 1.5 $" |
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45 | __date__ = "$Date: 2006/06/23 12:32:25 $" |
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46 | __license__ = 'Python license' |
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47 | |
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48 | # standard library modules |
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49 | import sys |
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50 | import threading |
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51 | import Queue |
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52 | |
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53 | # exceptions |
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54 | class NoResultsPending(Exception): |
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55 | """All work requests have been processed.""" |
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56 | pass |
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57 | |
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58 | class NoWorkersAvailable(Exception): |
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59 | """No worker threads available to process remaining requests.""" |
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60 | pass |
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61 | |
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62 | # classes |
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63 | class WorkerThread(threading.Thread): |
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64 | """Background thread connected to the requests/results queues. |
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65 | |
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66 | A worker thread sits in the background and picks up work requests from |
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67 | one queue and puts the results in another until it is dismissed. |
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68 | """ |
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69 | |
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70 | def __init__(self, requestsQueue, resultsQueue, **kwds): |
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71 | """Set up thread in daemonic mode and start it immediatedly. |
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72 | |
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73 | requestsQueue and resultQueue are instances of Queue.Queue passed |
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74 | by the ThreadPool class when it creates a new worker thread. |
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75 | """ |
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76 | |
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77 | threading.Thread.__init__(self, **kwds) |
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78 | self.setDaemon(1) |
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79 | self.workRequestQueue = requestsQueue |
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80 | self.resultQueue = resultsQueue |
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81 | self._dismissed = threading.Event() |
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82 | self.start() |
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83 | |
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84 | def run(self): |
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85 | """Repeatedly process the job queue until told to exit.""" |
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86 | |
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87 | while not self._dismissed.isSet(): |
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88 | # thread blocks here, if queue empty |
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89 | request = self.workRequestQueue.get() |
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90 | if self._dismissed.isSet(): |
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91 | # if told to exit, return the work request we just picked up |
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92 | self.workRequestQueue.put(request) |
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93 | break # and exit |
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94 | try: |
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95 | self.resultQueue.put( |
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96 | (request, request.callable(*request.args, **request.kwds)) |
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97 | ) |
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98 | except: |
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99 | request.exception = True |
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100 | self.resultQueue.put((request, sys.exc_info())) |
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101 | |
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102 | def dismiss(self): |
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103 | """Sets a flag to tell the thread to exit when done with current job. |
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104 | """ |
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105 | |
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106 | self._dismissed.set() |
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107 | |
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108 | |
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109 | class WorkRequest: |
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110 | """A request to execute a callable for putting in the request queue later. |
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111 | |
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112 | See the module function makeRequests() for the common case |
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113 | where you want to build several WorkRequests for the same callable |
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114 | but with different arguments for each call. |
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115 | """ |
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116 | |
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117 | def __init__(self, callable, args=None, kwds=None, requestID=None, |
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118 | callback=None, exc_callback=None): |
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119 | """Create a work request for a callable and attach callbacks. |
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120 | |
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121 | A work request consists of the a callable to be executed by a |
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122 | worker thread, a list of positional arguments, a dictionary |
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123 | of keyword arguments. |
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124 | |
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125 | A callback function can be specified, that is called when the results |
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126 | of the request are picked up from the result queue. It must accept |
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127 | two arguments, the request object and the results of the callable, |
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128 | in that order. If you want to pass additional information to the |
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129 | callback, just stick it on the request object. |
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130 | |
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131 | You can also give a callback for when an exception occurs. It should |
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132 | also accept two arguments, the work request and a tuple with the |
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133 | exception details as returned by sys.exc_info(). |
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134 | |
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135 | requestID, if given, must be hashable since it is used by the |
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136 | ThreadPool object to store the results of that work request in a |
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137 | dictionary. It defaults to the return value of id(self). |
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138 | """ |
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139 | |
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140 | if requestID is None: |
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141 | self.requestID = id(self) |
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142 | else: |
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143 | try: |
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144 | hash(requestID) |
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145 | except TypeError: |
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146 | raise TypeError("requestID must be hashable.") |
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147 | self.requestID = requestID |
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148 | self.exception = False |
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149 | self.callback = callback |
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150 | self.exc_callback = exc_callback |
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151 | self.callable = callable |
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152 | self.args = args or [] |
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153 | self.kwds = kwds or {} |
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154 | |
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155 | |
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156 | class ThreadPool: |
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157 | """A thread pool, distributing work requests and collecting results. |
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158 | |
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159 | See the module doctring for more information. |
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160 | """ |
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161 | |
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162 | def __init__(self, num_workers, q_size=0): |
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163 | """Set up the thread pool and start num_workers worker threads. |
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164 | |
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165 | num_workers is the number of worker threads to start initialy. |
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166 | If q_size > 0 the size of the work request queue is limited and |
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167 | the thread pool blocks when the queue is full and it tries to put |
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168 | more work requests in it (see putRequest method). |
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169 | """ |
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170 | |
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171 | self.requestsQueue = Queue.Queue(q_size) |
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172 | self.resultsQueue = Queue.Queue() |
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173 | self.workers = [] |
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174 | self.workRequests = {} |
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175 | self.createWorkers(num_workers) |
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176 | |
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177 | def createWorkers(self, num_workers): |
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178 | """Add num_workers worker threads to the pool.""" |
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179 | |
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180 | for i in range(num_workers): |
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181 | self.workers.append(WorkerThread(self.requestsQueue, |
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182 | self.resultsQueue)) |
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183 | |
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184 | def dismissWorkers(self, num_workers): |
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185 | """Tell num_workers worker threads to quit after their current task. |
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186 | """ |
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187 | |
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188 | for i in range(min(num_workers, len(self.workers))): |
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189 | worker = self.workers.pop() |
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190 | worker.dismiss() |
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191 | |
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192 | def putRequest(self, request, block=True, timeout=0): |
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193 | """Put work request into work queue and save its id for later.""" |
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194 | |
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195 | assert isinstance(request, WorkRequest) |
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196 | self.requestsQueue.put(item=request, block=block)#,timeout=timeout) |
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197 | self.workRequests[request.requestID] = request |
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198 | |
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199 | def poll(self, block=False): |
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200 | """Process any new results in the queue.""" |
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201 | |
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202 | while True: |
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203 | # still results pending? |
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204 | if not self.workRequests: |
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205 | raise NoResultsPending |
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206 | # are there still workers to process remaining requests? |
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207 | elif block and not self.workers: |
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208 | raise NoWorkersAvailable |
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209 | try: |
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210 | # get back next results |
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211 | request, result = self.resultsQueue.get(block=block) |
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212 | # has an exception occured? |
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213 | if request.exception and request.exc_callback: |
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214 | request.exc_callback(request, result) |
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215 | # hand results to callback, if any |
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216 | if request.callback and not \ |
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217 | (request.exception and request.exc_callback): |
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218 | request.callback(request, result) |
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219 | del self.workRequests[request.requestID] |
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220 | except Queue.Empty: |
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221 | break |
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222 | |
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223 | def wait(self): |
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224 | """Wait for results, blocking until all have arrived.""" |
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225 | while 1: |
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226 | try: |
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227 | self.poll(True) |
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228 | except NoResultsPending: |
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229 | break |
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230 | # helper functions |
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231 | def makeRequests(callable, args_list, callback=None, exc_callback=None): |
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232 | """Create several work requests for same callable with different arguments. |
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233 | |
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234 | Convenience function for creating several work requests for the same |
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235 | callable where each invocation of the callable receives different values |
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236 | for its arguments. |
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237 | |
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238 | args_list contains the parameters for each invocation of callable. |
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239 | Each item in 'args_list' should be either a 2-item tuple of the list of |
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240 | positional arguments and a dictionary of keyword arguments or a single, |
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241 | non-tuple argument. |
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242 | |
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243 | See docstring for WorkRequest for info on callback and exc_callback. |
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244 | """ |
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245 | |
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246 | requests = [] |
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247 | for item in args_list: |
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248 | if isinstance(item, tuple): |
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249 | requests.append( |
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250 | WorkRequest(callable, item[0], item[1], callback=callback, |
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251 | exc_callback=exc_callback) |
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252 | ) |
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253 | else: |
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254 | requests.append( |
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255 | WorkRequest(callable, [item], None, callback=callback, |
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256 | exc_callback=exc_callback) |
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257 | ) |
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258 | return requests |
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259 | |
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260 | |
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261 | #------------------------------ EoF ------------------------------# |
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