updated chapter 4 and appendix-A files

appendix-A/sha_futures.py

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+import sys
+import time
+import hashlib
+from concurrent import futures
+from random import randrange
+
+JOBS = 12
+SIZE = 2**20
+STATUS = '{} workers, elapsed time: {:.2f}s'
+
+
+def sha(size):
+    data = bytearray(randrange(256) for i in range(size))
+    algo = hashlib.new('sha256')
+    algo.update(data)
+    return algo.hexdigest()
+
+
+def main(workers=None):
+    if workers:
+        workers = int(workers)
+    t0 = time.time()
+
+    with futures.ProcessPoolExecutor(workers) as executor:
+        actual_workers = executor._max_workers
+        to_do = (executor.submit(sha, SIZE) for i in range(JOBS))
+        for future in futures.as_completed(to_do):
+            res = future.result()
+            print(res)
+
+    print(STATUS.format(actual_workers, time.time() - t0))
+
+if __name__ == '__main__':
+    if len(sys.argv) == 2:
+        workers = int(sys.argv[1])
+    else:
+        workers = None
+    main(workers)