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217615abf6
- Removed two unused variables.
- Changed `a` to `_` since the `a` variable is never used.
This addresses [3 alerts from lgtm](d55bbcd204/files/sorts/Odd-Even_transposition_parallel.py).
126 lines
3.9 KiB
Python
126 lines
3.9 KiB
Python
"""
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This is an implementation of odd-even transposition sort.
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It works by performing a series of parallel swaps between odd and even pairs of
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variables in the list.
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This implementation represents each variable in the list with a process and
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each process communicates with its neighboring processes in the list to perform
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comparisons.
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They are synchronized with locks and message passing but other forms of
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synchronization could be used.
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"""
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from multiprocessing import Process, Pipe, Lock
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#lock used to ensure that two processes do not access a pipe at the same time
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processLock = Lock()
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"""
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The function run by the processes that sorts the list
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position = the position in the list the prcoess represents, used to know which
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neighbor we pass our value to
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value = the initial value at list[position]
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LSend, RSend = the pipes we use to send to our left and right neighbors
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LRcv, RRcv = the pipes we use to receive from our left and right neighbors
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resultPipe = the pipe used to send results back to main
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"""
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def oeProcess(position, value, LSend, RSend, LRcv, RRcv, resultPipe):
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global processLock
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#we perform n swaps since after n swaps we know we are sorted
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#we *could* stop early if we are sorted already, but it takes as long to
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#find out we are sorted as it does to sort the list with this algorithm
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for i in range(0, 10):
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if( (i + position) % 2 == 0 and RSend != None):
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#send your value to your right neighbor
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processLock.acquire()
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RSend[1].send(value)
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processLock.release()
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#receive your right neighbor's value
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processLock.acquire()
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temp = RRcv[0].recv()
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processLock.release()
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#take the lower value since you are on the left
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value = min(value, temp)
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elif( (i + position) % 2 != 0 and LSend != None):
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#send your value to your left neighbor
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processLock.acquire()
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LSend[1].send(value)
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processLock.release()
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#receive your left neighbor's value
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processLock.acquire()
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temp = LRcv[0].recv()
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processLock.release()
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#take the higher value since you are on the right
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value = max(value, temp)
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#after all swaps are performed, send the values back to main
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resultPipe[1].send(value)
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"""
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the function which creates the processes that perform the parallel swaps
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arr = the list to be sorted
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"""
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def OddEvenTransposition(arr):
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processArray = []
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resultPipe = []
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#initialize the list of pipes where the values will be retrieved
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for _ in arr:
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resultPipe.append(Pipe())
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#creates the processes
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#the first and last process only have one neighbor so they are made outside
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#of the loop
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tempRs = Pipe()
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tempRr = Pipe()
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processArray.append(Process(target = oeProcess, args = (0, arr[0], None, tempRs, None, tempRr, resultPipe[0])))
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tempLr = tempRs
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tempLs = tempRr
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for i in range(1, len(arr) - 1):
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tempRs = Pipe()
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tempRr = Pipe()
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processArray.append(Process(target = oeProcess, args = (i, arr[i], tempLs, tempRs, tempLr, tempRr, resultPipe[i])))
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tempLr = tempRs
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tempLs = tempRr
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processArray.append(Process(target = oeProcess, args = (len(arr) - 1, arr[len(arr) - 1], tempLs, None, tempLr, None, resultPipe[len(arr) - 1])))
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#start the processes
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for p in processArray:
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p.start()
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#wait for the processes to end and write their values to the list
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for p in range(0, len(resultPipe)):
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arr[p] = resultPipe[p][0].recv()
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processArray[p].join()
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return(arr)
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#creates a reverse sorted list and sorts it
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def main():
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arr = []
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for i in range(10, 0, -1):
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arr.append(i)
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print("Initial List")
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print(*arr)
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list = OddEvenTransposition(arr)
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print("Sorted List\n")
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print(*arr)
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if __name__ == "__main__":
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main()
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