1 | """ |
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2 | |
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3 | @author: Christopher Arndt |
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4 | @version: 1.1 |
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5 | |
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6 | @see: http://aspn.activestate.com/ASPN/Cookbook/Python/Recipe/435883 |
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7 | |
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8 | Easy to use object-oriented thread pool framework. |
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9 | |
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10 | A thread pool is a class that maintains a pool of worker threads to perform |
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11 | time consuming operations in parallel. It assigns jobs to the threads |
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12 | by putting them in a work request queue, where they are picked up by the |
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13 | next available thread. This then performs the requested operation in the |
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14 | background and puts the results in a another queue. |
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15 | |
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16 | The thread pool class can then collect the results from all threads from |
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17 | this queue as soon as they become available or after all threads have |
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18 | finished their work. It's also possible, to define callbacks to handle |
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19 | each result as it comes in. |
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20 | |
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21 | The basic concept and some code was taken from the book "Python in a Nutshell" |
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22 | by Alex Martelli, copyright 2003, ISBN 0-596-00188-6, from section 14.5 |
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23 | "Threaded Program Architecture". I wrapped the main program logic in the |
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24 | ThreadPool class, added the WorkRequest class and the callback system and |
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25 | tweaked the code here and there. |
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26 | |
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27 | Basic usage: |
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28 | |
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29 | >>> main = ThreadPool(poolsize) |
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30 | >>> requests = makeRequests(some_callable, list_of_args, callback) |
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31 | >>> [main.putRequests(req) for req in requests] |
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32 | >>> main.wait() |
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33 | |
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34 | See the end of the module code for a brief, annotated usage example. |
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35 | """ |
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36 | |
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37 | __all__ = ['makeRequests', 'NoResultsPending', 'NoWorkersAvailable', |
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38 | 'ThreadPool', 'WorkRequest', 'WorkerThread'] |
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39 | |
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40 | __author__ = 'Christopher Arndt' |
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41 | __version__ = '1.1' |
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42 | __date__ = '2005-07-19' |
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43 | |
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44 | import threading, Queue |
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45 | |
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46 | class NoResultsPending(Exception): |
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47 | """All work requests have been processed.""" |
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48 | pass |
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49 | class NoWorkersAvailable(Exception): |
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50 | """No worker threads available to process remaining requests.""" |
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51 | pass |
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52 | |
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53 | class WorkerThread(threading.Thread): |
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54 | """Background thread connected to the requests/results queues. |
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55 | |
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56 | A worker thread sits in the background and picks up work requests from |
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57 | one queue and puts the results in another until it is dismissed. |
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58 | """ |
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59 | |
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60 | def __init__ (self, requestsQueue, resultsQueue, **kwds): |
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61 | """Set up thread in damonic mode and start it immediatedly. |
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62 | |
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63 | requestsQueue and resultQueue are instances of Queue.Queue passed |
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64 | by the ThreadPool class when it creates a new worker thread. |
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65 | """ |
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66 | threading.Thread.__init__(self, **kwds) |
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67 | self.setDaemon(1) |
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68 | self.workRequestQueue = requestsQueue |
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69 | self.resultQueue = resultsQueue |
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70 | self._dismissed = threading.Event() |
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71 | self.start() |
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72 | |
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73 | def run(self): |
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74 | """Repeatedly process the job queue until told to exit. |
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75 | """ |
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76 | |
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77 | while not self._dismissed.isSet(): |
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78 | # thread blocks here, if queue empty |
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79 | request = self.workRequestQueue.get() |
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80 | if self._dismissed.isSet(): |
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81 | # return the work request we just picked up |
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82 | self.workRequestQueue.put(request) |
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83 | break # and exit |
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84 | # XXX catch exceptions here and stick them to request object |
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85 | self.resultQueue.put( |
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86 | (request, request.callable(*request.args, **request.kwds)) |
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87 | ) |
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88 | |
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89 | def dismiss(self): |
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90 | """Sets a flag to tell the thread to exit when done with current job. |
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91 | """ |
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92 | |
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93 | self._dismissed.set() |
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94 | |
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95 | |
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96 | class WorkRequest: |
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97 | """A request to execute a callable for putting in the request queue later. |
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98 | |
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99 | See the module function makeRequests() for the common case |
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100 | where you want to build several work requests for the same callable |
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101 | but different arguments for each call. |
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102 | """ |
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103 | |
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104 | def __init__ (self, callable, args=None, kwds=None, requestID=None, |
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105 | callback=None): |
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106 | """A work request consists of the a callable to be executed by a |
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107 | worker thread, a list of positional arguments, a dictionary |
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108 | of keyword arguments. |
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109 | |
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110 | A callback function can be specified, that is called when the results |
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111 | of the request are picked up from the result queue. It must accept |
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112 | two arguments, the request object and it's results in that order. |
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113 | If you want to pass additional information to the callback, just stick |
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114 | it on the request object. |
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115 | |
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116 | requestID, if given, must be hashable as it is used by the ThreadPool |
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117 | class to store the results of that work request in a dictionary. |
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118 | It defaults to the return value of id(self). |
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119 | """ |
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120 | if requestID is None: |
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121 | self.requestID = id(self) |
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122 | else: |
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123 | self.requestID = requestID |
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124 | self.callback = callback |
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125 | self.callable = callable |
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126 | self.args = args or [] |
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127 | self.kwds = kwds or {} |
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128 | |
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129 | |
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130 | class ThreadPool: |
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131 | """A thread pool, distributing work requests and collecting results. |
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132 | |
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133 | See the module doctring for more information. |
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134 | """ |
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135 | |
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136 | def __init__ (self, num_workers, q_size=0): |
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137 | """Set up the thread pool and start num_workers worker threads. |
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138 | |
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139 | num_workers is the number of worker threads to start initialy. |
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140 | If q_size > 0 the size of the work request is limited and the |
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141 | thread pool blocks when queue is full and it tries to put more |
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142 | work requests in it. |
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143 | """ |
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144 | |
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145 | self.requestsQueue = Queue.Queue(q_size) |
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146 | self.resultsQueue = Queue.Queue() |
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147 | self.workers = [] |
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148 | self.workRequests = {} |
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149 | self.createWorkers(num_workers) |
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150 | |
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151 | def createWorkers(self, num_workers): |
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152 | """Add num_workers worker threads to the pool.""" |
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153 | |
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154 | for i in range(num_workers): |
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155 | self.workers.append(WorkerThread(self.requestsQueue, |
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156 | self.resultsQueue)) |
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157 | |
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158 | def dismissWorkers(self, num_workers): |
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159 | """Tell num_workers worker threads to to quit when they're done.""" |
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160 | |
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161 | for i in range(min(num_workers, len(self.workers))): |
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162 | worker = self.workers.pop() |
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163 | worker.dismiss() |
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164 | |
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165 | def putRequest(self, request): |
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166 | """Put work request into work queue and save for later.""" |
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167 | self.requestsQueue.put(request) |
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168 | self.workRequests[request.requestID] = request |
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169 | |
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170 | def poll(self, block=False): |
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171 | """Process any new results in the queue.""" |
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172 | while 1: |
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173 | try: |
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174 | # still results pending? |
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175 | if not self.workRequests: |
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176 | raise NoResultsPending |
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177 | # are there still workers to process remaining requests? |
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178 | elif block and not self.workers: |
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179 | raise NoWorkersAvailable |
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180 | # get back next results |
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181 | request, result = self.resultsQueue.get(block=block) |
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182 | # and hand them to the callback, if any |
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183 | if request.callback: |
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184 | request.callback(request, result) |
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185 | del self.workRequests[request.requestID] |
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186 | except Queue.Empty: |
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187 | break |
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188 | |
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189 | def wait(self): |
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190 | """Wait for results, blocking until all have arrived.""" |
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191 | |
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192 | while 1: |
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193 | try: |
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194 | self.poll(True) |
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195 | except NoResultsPending: |
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196 | break |
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197 | |
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198 | def makeRequests(callable, args_list, callback=None): |
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199 | """Convenience function for building several work requests for the same |
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200 | callable with different arguments for each call. |
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201 | |
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202 | args_list contains the parameters for each invocation of callable. |
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203 | Each item in 'argslist' should be either a 2-item tuple of the list of |
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204 | positional arguments and a dictionary of keyword arguments or a single, |
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205 | non-tuple argument. |
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206 | |
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207 | callback is called when the results arrive in the result queue. |
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208 | """ |
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209 | |
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210 | requests = [] |
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211 | |
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212 | for item in args_list: |
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213 | |
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214 | if item is None: |
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215 | """no arguments""" |
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216 | requests.append( |
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217 | WorkRequest(callable, None, None, callback=callback)) |
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218 | |
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219 | elif item == isinstance(item, tuple): |
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220 | """arguments and keywords""" |
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221 | requests.append( |
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222 | WorkRequest(callable, item[0], item[1], callback=callback)) |
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223 | else: |
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224 | """only keywords""" |
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225 | requests.append( |
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226 | WorkRequest(callable, [item], None, callback=callback)) |
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227 | return requests |
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228 | |
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229 | |
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230 | if __name__ == '__main__': |
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231 | import random |
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232 | import time |
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233 | |
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234 | # the work the threads will have to do (rather trivial in our example) |
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235 | def do_something(data): |
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236 | time.sleep(random.randint(1,5)) |
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237 | return round(random.random() * data, 5) |
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238 | |
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239 | # this will be called each time a result is available |
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240 | def print_result(request, result): |
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241 | print "Result: %s from request #%s" % (result, request.requestID) |
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242 | |
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243 | # assemble the arguments for each job to a list... |
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244 | data = [random.randint(1,10) for i in range(20)] |
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245 | # ... and build a WorkRequest object for each item in data |
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246 | requests = makeRequests(do_something, data, print_result) |
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247 | |
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248 | # we create a pool of 10 worker threads |
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249 | main = ThreadPool(3) |
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250 | |
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251 | # then we put the work requests in the queue... |
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252 | for req in requests: |
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253 | main.putRequest(req) |
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254 | print "Work request #%s added." % req.requestID |
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255 | # or shorter: |
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256 | # [main.putRequest(req) for req in requests] |
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257 | |
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258 | # ...and wait for the results to arrive in the result queue |
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259 | # wait() will return when results for all work requests have arrived |
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260 | # main.wait() |
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261 | |
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262 | # alternatively poll for results while doing something else: |
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263 | i = 0 |
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264 | while 1: |
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265 | try: |
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266 | main.poll() |
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267 | print "Main thread working..." |
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268 | time.sleep(0.5) |
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269 | if i == 10: |
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270 | print "Adding 3 more worker threads..." |
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271 | main.createWorkers(3) |
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272 | i += 1 |
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273 | except (KeyboardInterrupt, NoResultsPending): |
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274 | break |
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