examples for ch.20: Concurrency Models

20-concurrency/primes/spinner_thread.py

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+# spinner_thread.py
+
+# credits: Adapted from Michele Simionato's
+# multiprocessing example in the python-list:
+# https://mail.python.org/pipermail/python-list/2009-February/675659.html
+
+# tag::SPINNER_THREAD_TOP[]
+from threading import Thread, Event
+import itertools
+import time
+
+from primes import is_prime
+
+def spin(msg: str, done: Event) -> None:  # <1>
+    for char in itertools.cycle(r'\|/-'):  # <2>
+        status = f'\r{char} {msg}'  # <3>
+        print(status, end='', flush=True)
+        if done.wait(.1):  # <4>
+            break  # <5>
+    blanks = ' ' * len(status)
+    print(f'\r{blanks}\r', end='')  # <6>
+
+def slow() -> int:
+    is_prime(5_000_111_000_222_021)  # <7>
+    return 42
+# end::SPINNER_THREAD_TOP[]
+
+# tag::SPINNER_THREAD_REST[]
+def supervisor() -> int:  # <1>
+    done = Event()  # <2>
+    spinner = Thread(target=spin,
+                     args=('thinking!', done))  # <3>
+    print('spinner object:', spinner)  # <4>
+    spinner.start()  # <5>
+    result = slow()  # <6>
+    done.set()  # <7>
+    spinner.join()  # <8>
+    return result
+
+def main() -> None:
+    result = supervisor()  # <9>
+    print('Answer:', result)
+
+if __name__ == '__main__':
+    main()
+# end::SPINNER_THREAD_REST[]