{"id":1697,"date":"2020-12-17T04:53:48","date_gmt":"2020-12-17T04:53:48","guid":{"rendered":"https:\/\/www.pythontutorial.net\/?page_id=1697"},"modified":"2023-06-04T08:57:28","modified_gmt":"2023-06-04T08:57:28","slug":"python-threading","status":"publish","type":"page","link":"https:\/\/www.pythontutorial.net\/python-concurrency\/python-threading\/","title":{"rendered":"Python Threading"},"content":{"rendered":"\n

Summary<\/strong>: in this tutorial, you’ll learn how to use the Python threading module to develop multi-threaded applications.<\/p>\n\n\n\n

Single-threaded applications #<\/a><\/h2>\n\n\n\n

Let’s start with a simple program:<\/p>\n\n\n

from<\/span> time import<\/span> sleep, perf_counter\n\ndef<\/span> task<\/span>()<\/span>:<\/span>\n    print('Starting a task...'<\/span>)\n    sleep(1<\/span>)\n    print('done'<\/span>)\n\n\nstart_time = perf_counter()\n\ntask()\ntask()\n\nend_time = perf_counter()\n\nprint(f'It took {end_time- start_time: 0.2<\/span>f}<\/span> second(s) to complete.'<\/span>)\n<\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
How it works.<\/p>\n\n\n\n
First, import the sleep()<\/code> and perf_counter()<\/code> functions from the time<\/code> module:<\/p>\n\n\n
from<\/span> time import<\/span> sleep, perf_counter<\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
def<\/span> task<\/span>()<\/span>:<\/span>\n    print('Starting a task...'<\/span>)\n    sleep(1<\/span>)\n    print('done'<\/span>)<\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
Third, get the value of the performance counter by calling the perf_counter()<\/code> function:<\/p>\n\n\n
start_time = perf_counter()       <\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
Fourth, call the task()<\/code> function twice:<\/p>\n\n\n
task()\ntask()<\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
Fifth, get the value of the performance counter by calling the perf_counter()<\/code> function:<\/p>\n\n\n
end_time = perf_counter()<\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
Finally, output the time that takes to complete running the task()<\/code> function twice:<\/p>\n\n\n
print(f'It took {end_time- start_time: 0.2<\/span>f}<\/span> second(s) to complete.'<\/span>)<\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
Here is the output:<\/p>\n\n\n
Starting a task...\ndone\nStarting a task...\ndone\nIt took  2.00<\/span> second(s) to complete.<\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
As you may expect, the program takes about two seconds to complete. If you call the task()<\/code> function 10 times, it would take about 10 seconds to complete.<\/p>\n\n\n\n
The following diagram illustrates how the program works:<\/p>\n\n\n\n
\"\"<\/figure>\n\n\n\n
First, the task()<\/code> function executes and sleeps for one second. Then it executes the second time and also sleeps for another second. Finally, the program completes.<\/p>\n\n\n\n
When the task()<\/code> function calls the sleep()<\/code> function, the CPU is idle. In other words, the CPU doesn’t do anything, which is not efficient in terms of resource utilization.<\/p>\n\n\n\n
This program has one process with a single thread, which is called the main thread<\/strong>. Because the program has only one thread, it’s called a single-threaded program.<\/p>\n\n\n\n
Using Python threading to develop a multi-threaded program example #<\/a><\/h2>\n\n\n\n
To create a multi-threaded program, you need to use the Python threading<\/code> module.<\/p>\n\n\n\n
First, import the Thread<\/code> class from the threading<\/code> module:<\/p>\n\n\n
from<\/span> threading import<\/span> Thread<\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
Second, create a new thread by instantiating an instance of the Thread<\/code> class:<\/p>\n\n\n
new_thread = Thread(target=fn,args=args_tuple)<\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
The Thread()<\/code> accepts many parameters. The main ones are:<\/p>\n\n\n\n
Second, define a function<\/a> that takes one second to complete:<\/p>\n\n\n