[Tutor] Fwd: Concept of multithreading

[Dennis Lee Bieber]

On Mon, 23 Aug 2021 16:59:31 -0400, Dennis Lee Bieber
<wlfraed at ix.netcom.com> declaimed the following:

>	Note that the time output is wall-clock durations, and mostly counts
>the time spent sleeping (or for main thread, blocked trying to queue the
>next value).

	I tried changing the time.perf_counter() into time.thread_time_ns() and
time.process_time_ns(), neither of which include the time spent in sleep()
(nor, I suspect, any other blocking operation), but so little work is
actually done each time the thread(s) wake up that the accumulated times
came out as 0ns. This even after I doubled the work, cut the sleep() times
to average 0.5s, and moved the generation of random integers and random
sleep times /into/ the worker threads. The main thread is just queuing
integers to wake up the workers -- the integer is otherwise ignored.

-=-=-=-
C:\Users\Wulfraed\Documents\_Hg-Repositories\Python Progs>Q_Threads.py
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Worker: 2       Sum: 22722      Number Values: 181      Time: 83.207052
Worker: 0       Sum: 17799      Number Values: 151      Time:
83.56292210000001
Worker: 1       Sum: 21747      Number Values: 168      Time: 83.8785809
Total time: 83.8851056

C:\Users\Wulfraed\Documents\_Hg-Repositories\Python Progs>
-=-=-=-
DIFF format rather than full listing of source...

@@ -11,5 +11,6 @@
 
 DONE = object()
 NUMWORKERS = 3
-NUMVALUES = 250     #with average sleep of 1.0 second, will take 4 minutes
to complete
+NUMVALUES = 500     #with average sleep of 0.5 second, will take 4 minutes
to complete
+                    #IF done linearly. with three threads, about 85
seconds each
 
@@ -15,4 +16,7 @@
 
+#tried using time.thread_time and time.process_time as they do not count
+#time spent in sleep() or otherwise blocked, but the degree of work done
+#on each cycle is so small the accumulated times were 0.0!
 def worker(id, inQ, outQ):
     sumv = 0
     numv = 0
@@ -16,7 +20,7 @@
 def worker(id, inQ, outQ):
     sumv = 0
     numv = 0
-    startPC = time.perf_counter()
+    start = time.perf_counter()
     while True:
         vlu = inQ.get()
         if vlu == DONE: break
@@ -20,5 +24,7 @@
     while True:
         vlu = inQ.get()
         if vlu == DONE: break
-        sumv += vlu[0]
+        #increment count of processed items
+        #generate random value ("work")
+        #generate random sleep between 0 and 1 second
         numv += 1
@@ -24,4 +30,6 @@
         numv += 1
-        time.sleep(vlu[1])
-    inQ.put(vlu)    #propagate the DONE flag to next
+        sumv += random.randint(1, NUMVALUES // 2)
+        time.sleep(random.random())
+    inQ.put(vlu)    #propagate the DONE flag to next thread
+    #return results
     outQ.put((id, sumv, numv,
@@ -27,3 +35,3 @@
     outQ.put((id, sumv, numv,
-              time.perf_counter() - startPC))
+              time.perf_counter() - start))
 
@@ -29,8 +37,8 @@
 
-startPC = time.perf_counter()
+start = time.perf_counter()
 
 threads = [threading.Thread(target=worker, args=(i, inQueue, outQueue))
for i in range(NUMWORKERS)]
 
 for t in threads:
     t.start()
 
@@ -31,13 +39,12 @@
 
 threads = [threading.Thread(target=worker, args=(i, inQueue, outQueue))
for i in range(NUMWORKERS)]
 
 for t in threads:
     t.start()
 
-for _ in range(NUMVALUES):
-    v = random.randint(1, NUMVALUES // 2)
-    s = random.random() * 2.0
-    inQueue.put((v, s))     #will block if 10 items are in the queue,
letting thread(s) run
+for i in range(NUMVALUES):
+    #i is put in queue only to release next worker, it is otherwise
meaningless
+    inQueue.put(i)     #will block if 10 items are in the queue, letting
thread(s) run
     print(". ", end="", flush=True)  #progress indicator
 
 print("\n\n")
@@ -52,5 +59,5 @@
     print("Worker: %s\tSum: %s\tNumber Values: %s\tTime: %s"
           % (id, sm, nm, dur))
 
-print("Total timePC: %s" %
-      (time.perf_counter() - startPC))
+print("Total time: %s" %
+      (time.perf_counter() - start))


-- 
	Wulfraed                 Dennis Lee Bieber         AF6VN
	wlfraed at ix.netcom.com    http://wlfraed.microdiversity.freeddns.org/