From 92a6a9b149e9fac610282df6304cfb792bfb89c2 Mon Sep 17 00:00:00 2001 From: Raymond Hettinger Date: Sun, 17 Oct 2021 17:23:51 -0500 Subject: [PATCH 1/2] Improve multiserver queue recipe --- Doc/library/random.rst | 10 +++++----- 1 file changed, 5 insertions(+), 5 deletions(-) diff --git a/Doc/library/random.rst b/Doc/library/random.rst index 0ac0fe72dc3929..4a82f852588908 100644 --- a/Doc/library/random.rst +++ b/Doc/library/random.rst @@ -503,7 +503,7 @@ between the effects of a drug versus a placebo:: Simulation of arrival times and service deliveries for a multiserver queue:: - from heapq import heappush, heappop + from heapq import heapreplace from random import expovariate, gauss from statistics import mean, quantiles @@ -515,14 +515,14 @@ Simulation of arrival times and service deliveries for a multiserver queue:: waits = [] arrival_time = 0.0 servers = [0.0] * num_servers # time when each server becomes available - for i in range(100_000): + for i in range(1_000_000): arrival_time += expovariate(1.0 / average_arrival_interval) - next_server_available = heappop(servers) + next_server_available = servers[0] wait = max(0.0, next_server_available - arrival_time) waits.append(wait) - service_duration = gauss(average_service_time, stdev_service_time) + service_duration = max(0.0, gauss(average_service_time, stdev_service_time)) service_completed = arrival_time + wait + service_duration - heappush(servers, service_completed) + heapreplace(servers, service_completed) print(f'Mean wait: {mean(waits):.1f} Max wait: {max(waits):.1f}') print('Quartiles:', [round(q, 1) for q in quantiles(waits)]) From 950b96264004fb3ec96cd79292f76e7c4dccc0a2 Mon Sep 17 00:00:00 2001 From: Raymond Hettinger Date: Sun, 17 Oct 2021 17:40:32 -0500 Subject: [PATCH 2/2] Heapify the start times --- Doc/library/random.rst | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/Doc/library/random.rst b/Doc/library/random.rst index 4a82f852588908..36f232dc319e40 100644 --- a/Doc/library/random.rst +++ b/Doc/library/random.rst @@ -503,7 +503,7 @@ between the effects of a drug versus a placebo:: Simulation of arrival times and service deliveries for a multiserver queue:: - from heapq import heapreplace + from heapq import heapify, heapreplace from random import expovariate, gauss from statistics import mean, quantiles @@ -515,6 +515,7 @@ Simulation of arrival times and service deliveries for a multiserver queue:: waits = [] arrival_time = 0.0 servers = [0.0] * num_servers # time when each server becomes available + heapify(servers) for i in range(1_000_000): arrival_time += expovariate(1.0 / average_arrival_interval) next_server_available = servers[0]