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| # CWE-400: Uncontrolled Resource Consumption | ||
| Canceling the task in a thread pool only prevents it from being executed if it has not started yet. For the task to be interruptible, it must handle the `threading.Event` flag. | ||
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| ## Non-Compliant Code Example | ||
| Tasks can be submitted to the ThreadPoolExecutor by calling `submit()`. Submitted tasks can be canceled by calling `cancel()` on the Future object returned by `submit()`. Calling this method will return True and stop the task from being executed if it has not started yet. However, if its execution has already started, calling `cancel()` will instead return False and will not stop the task [Python 3.10 docs on Future.cancel]. | ||
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| [*noncompliant01.py:*](noncompliant01.py) | ||
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| ```py | ||
| """ Non-compliant Code Example """ | ||
| import time | ||
| from concurrent.futures import ThreadPoolExecutor | ||
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| def take_time(x): | ||
| print(f"Started Task: {x}") | ||
| # Simulate work | ||
| for i in range(10): | ||
| time.sleep(1) | ||
| print(f"Completed Task: {x}") | ||
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| def run_thread(_executor, var): | ||
| future = _executor.submit(take_time, var) | ||
| return future | ||
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| def interrupt(future): | ||
| print(future.cancel()) | ||
| print(f"Interrupted: {future}") | ||
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| ##################### | ||
| # Exploiting above code example | ||
| ##################### | ||
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| with ThreadPoolExecutor() as executor: | ||
| task = run_thread(executor, "A") | ||
| interrupt(task) | ||
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| ``` | ||
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| ## Compliant Solution | ||
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| Tasks submitted to the ThreadPoolExecutor can be interrupted by setting a thread-safe flag, such as `threading.Event` [Python 3.10 docs on threading.Event]. An Event object should be passed as an argument to the submitted task. From within the task function, we need to manually check the flag status by calling `event.is_set()` and handling the interruption. In order to set the Event flag, we can call `event.set()` on the event object. | ||
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| [*compliant01.py:*](compliant01.py) | ||
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| ```py | ||
| """ Compliant Code Example """ | ||
| import time | ||
| from concurrent.futures import ThreadPoolExecutor | ||
| from threading import Event | ||
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| def take_time(x, _event): | ||
| print(f"Started Task: {x}") | ||
| # Simulate work | ||
| for _ in range(10): | ||
| if _event.is_set(): | ||
| print(f"Interrupted Task: {x}") | ||
| # Save partial results | ||
| return | ||
| time.sleep(1) | ||
| print(f"Completed Task: {x}") | ||
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| def run_thread(_executor, var): | ||
| e = Event() | ||
| future = _executor.submit(take_time, var, e) | ||
| return future, e | ||
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| def interrupt(future, e): | ||
| """Cancel the task, just in case it is not yet running, and set the Event flag""" | ||
| future.cancel() | ||
| e.set() | ||
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| ##################### | ||
| # Exploiting above code example | ||
| ##################### | ||
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| with ThreadPoolExecutor() as executor: | ||
| task, event = run_thread(executor, "A") | ||
| interrupt(task, event) | ||
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| ``` | ||
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| ## Related Guidelines | ||
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| |:---|:---| | ||
| |[MITRE CWE](http://cwe.mitre.org/)|Pillar [CWE-664: Improper Control of a Resource Through its Lifetime (4.13) (mitre.org)](https://cwe.mitre.org/data/definitions/664.html)| | ||
| |[MITRE CWE](http://cwe.mitre.org/)|Class [CWE-400: Uncontrolled Resource Consumption (4.12)](https://cwe.mitre.org/data/definitions/400.html)| | ||
| |[SEI CERT Coding Standard for Java](https://wiki.sei.cmu.edu/confluence/display/java/SEI+CERT+Oracle+Coding+Standard+for+Java)|[TPS02-J. Ensure that tasks submitted to a thread pool are interruptible](https://wiki.sei.cmu.edu/confluence/display/java/TPS02-J.+Ensure+that+tasks+submitted+to+a+thread+pool+are+interruptible)| | ||
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| ## Biblography | ||
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| |:---|:---| | ||
| |[[Python 3.10.4 docs Future.cancel]](https://docs.python.org/)|[concurrent.futures — Launching parallel tasks — Python 3.10.4 documentation](https://docs.python.org/3/library/concurrent.futures.html)| | ||
| |[[Python 3.10.4 docs on threading.Event]](https://docs.python.org/)|[threading — Thread-based parallelism - Event Objects](https://docs.python.org/3/library/threading.html#event-objects)| |
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