os_cp:threads
Differences
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os_cp:threads [2025/04/25 13:11] jkonczak [Critical sections, deadlocks] |
os_cp:threads [2025/04/25 13:55] (current) jkonczak [POSIX condition variables] |
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| When one thread needs to execute some logic once a specific condition is fulfilled, | When one thread needs to execute some logic once a specific condition is fulfilled, | ||
| it should: | it should: | ||
| + | <html><div style="margin-top:-1.2em"></div></html> | ||
| + | <WRAP group> | ||
| + | <WRAP half column> | ||
| - lock a mutex, | - lock a mutex, | ||
| - check the condition, | - check the condition, | ||
| - | - if the condition is false: | + | - while the condition is false: |
| - wait on a condition variable, | - wait on a condition variable, | ||
| - go back to step 2, | - go back to step 2, | ||
| - do the logic, | - do the logic, | ||
| - unlock the mutex. | - unlock the mutex. | ||
| + | </WRAP> | ||
| + | <WRAP half column> | ||
| + | <html> | ||
| + | <pre class="code c" style="margin-top:-1.4em;margin-bottom:-1.4em;"> | ||
| + | <span style="opacity:0.66">pthread_mutex_</span>lock<span class="br0">(</span><span class="sy0">&</span>mutex<span class="br0">)</span><span class="sy0">;</span> | ||
| + | <span class="kw1">while</span><span class="br0">(</span><span class="sy0">!</span><i>condition</i><span class="br0">)</span> | ||
| + | <span style="opacity:0.66">pthread_cond_</span>wait<span class="br0">(</span><span class="sy0">&</span>condvar<span class="sy0">,</span> <span class="sy0">&</span>mutex<span class="br0">)</span><span class="sy0">;</span> | ||
| + | <i>logic<span class="br0">(</span><span class="br0">)</span><span class="sy0">;</span></i> | ||
| + | <span style="opacity:0.66">pthread_mutex_</span>unlock<span class="br0">(</span><span class="sy0">&</span>mutex<span class="br0">)</span><span class="sy0">;</span> | ||
| + | </pre> | ||
| + | </html> | ||
| + | </WRAP> | ||
| + | </WRAP> | ||
| A thread that may change the state and thus affect the condition should: | A thread that may change the state and thus affect the condition should: | ||
| + | <html><div style="margin-top:-1.2em"></div></html> | ||
| + | <WRAP group> | ||
| + | <WRAP half column> | ||
| - lock the mutex, | - lock the mutex, | ||
| - do its logic, | - do its logic, | ||
| - signal the condition variable, | - signal the condition variable, | ||
| - unlock the mutex((One can also signal the condition variable after unlocking the mutex.)). | - unlock the mutex((One can also signal the condition variable after unlocking the mutex.)). | ||
| + | </WRAP> | ||
| + | <WRAP half column> | ||
| + | <html> | ||
| + | <pre class="code c" style="padding-top:0; padding-bottom:0; margin-top:-1.4em;margin-bottom:-1.4em;"> | ||
| + | <span style="opacity:0.66">pthread_mutex_</span>lock<span class="br0">(</span><span class="sy0">&</span>mutex<span class="br0">)</span><span class="sy0">;</span> | ||
| + | <i>logic_that_changes_condition<span class="br0">(</span><span class="br0">)</span><span class="sy0">;</span></i> | ||
| + | <span style="opacity:0.66">pthread_cond_</span>signal<span class="br0">(</span><span class="sy0">&</span>condvar<span class="br0">)</span><span class="sy0">;</span> | ||
| + | <span style="opacity:0.66">pthread_mutex_</span>unlock<span class="br0">(</span><span class="sy0">&</span>mutex<span class="br0">)</span><span class="sy0">;</span> | ||
| + | </pre> | ||
| + | </html> | ||
| + | </WRAP> | ||
| + | </WRAP> | ||
| <small> | <small> | ||
| The example conditions include: | The example conditions include: | ||
| + | <html><div style="margin-top:-1.2em"></div></html> | ||
| * a boolean flag is set; the flag indicates that another thread finished a part of the computation and the results can used, | * a boolean flag is set; the flag indicates that another thread finished a part of the computation and the results can used, | ||
| * a list of items is not empty; the list contains tasks to be done by this thread, | * a list of items is not empty; the list contains tasks to be done by this thread, | ||
os_cp/threads.txt · Last modified: 2025/04/25 13:55 by jkonczak
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