mirror of https://github.com/t1meshift/os_labs.git
232 lines
9.5 KiB
Markdown
232 lines
9.5 KiB
Markdown
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# Лабораторная работа №9
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## Задание 2
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Команда запуска:
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`valgrind --tool=helgrind ./lab9_main-race_run`
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Результат:
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```text
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...
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==4862== Possible data race during read of size 4 at 0x30A014 by thread #1
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==4862== Locks held: none
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==4862== at 0x108D27: main (main-race.c:15)
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==4862==
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==4862== This conflicts with a previous write of size 4 by thread #2
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==4862== Locks held: none
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==4862== at 0x108CDF: worker (main-race.c:8)
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==4862== by 0x4C36C26: ??? (in /usr/lib/valgrind/vgpreload_helgrind-amd64-linux.so)
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==4862== by 0x4E496DA: start_thread (pthread_create.c:463)
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==4862== by 0x518288E: clone (clone.S:95)
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==4862== Address 0x30a014 is 0 bytes inside data symbol "balance"
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...
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```
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helgrind сообщает, что возможно использование переменной balance в двух потоках параллельно.
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### Решение проблемы:
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Блокировать незащищенный процесс.
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Заменить:
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```c
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balance++;
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```
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на:
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```c
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Pthread_mutex_lock(&m); // блокировка мьютекса
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balance++;
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Pthread_mutex_unlock(&m); // разблокировка
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```
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## Задание 3
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Команда запуска:
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`valgrind --tool=helgrind ./lab9_main-deadlock_run`
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Результат:
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```text
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...
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==6272== Thread #3: lock order "0x30A040 before 0x30A080" violated
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==6272==
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==6272== Observed (incorrect) order is: acquisition of lock at 0x30A080
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==6272== at 0x4C3403C: ??? (in /usr/lib/valgrind/vgpreload_helgrind-amd64-linux.so)
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==6272== by 0x108AD7: Pthread_mutex_lock (mythreads.h:23)
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==6272== by 0x108D06: worker (main-deadlock.c:13)
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==6272== by 0x4C36C26: ??? (in /usr/lib/valgrind/vgpreload_helgrind-amd64-linux.so)
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==6272== by 0x4E496DA: start_thread (pthread_create.c:463)
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==6272== by 0x518288E: clone (clone.S:95)
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==6272==
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==6272== followed by a later acquisition of lock at 0x30A040
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==6272== at 0x4C3403C: ??? (in /usr/lib/valgrind/vgpreload_helgrind-amd64-linux.so)
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==6272== by 0x108AD7: Pthread_mutex_lock (mythreads.h:23)
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==6272== by 0x108D12: worker (main-deadlock.c:14)
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==6272== by 0x4C36C26: ??? (in /usr/lib/valgrind/vgpreload_helgrind-amd64-linux.so)
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==6272== by 0x4E496DA: start_thread (pthread_create.c:463)
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==6272== by 0x518288E: clone (clone.S:95)
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==6272==
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==6272== Required order was established by acquisition of lock at 0x30A040
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==6272== at 0x4C3403C: ??? (in /usr/lib/valgrind/vgpreload_helgrind-amd64-linux.so)
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==6272== by 0x108AD7: Pthread_mutex_lock (mythreads.h:23)
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==6272== by 0x108CEC: worker (main-deadlock.c:10)
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==6272== by 0x4C36C26: ??? (in /usr/lib/valgrind/vgpreload_helgrind-amd64-linux.so)
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==6272== by 0x4E496DA: start_thread (pthread_create.c:463)
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==6272== by 0x518288E: clone (clone.S:95)
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==6272==
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==6272== followed by a later acquisition of lock at 0x30A080
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==6272== at 0x4C3403C: ??? (in /usr/lib/valgrind/vgpreload_helgrind-amd64-linux.so)
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==6272== by 0x108AD7: Pthread_mutex_lock (mythreads.h:23)
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==6272== by 0x108CF8: worker (main-deadlock.c:11)
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==6272== by 0x4C36C26: ??? (in /usr/lib/valgrind/vgpreload_helgrind-amd64-linux.so)
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==6272== by 0x4E496DA: start_thread (pthread_create.c:463)
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==6272== by 0x518288E: clone (clone.S:95)
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==6272==
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==6272== Lock at 0x30A040 was first observed
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==6272== at 0x4C3403C: ??? (in /usr/lib/valgrind/vgpreload_helgrind-amd64-linux.so)
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==6272== by 0x108AD7: Pthread_mutex_lock (mythreads.h:23)
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==6272== by 0x108CEC: worker (main-deadlock.c:10)
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==6272== by 0x4C36C26: ??? (in /usr/lib/valgrind/vgpreload_helgrind-amd64-linux.so)
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==6272== by 0x4E496DA: start_thread (pthread_create.c:463)
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==6272== by 0x518288E: clone (clone.S:95)
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==6272== Address 0x30a040 is 0 bytes inside data symbol "m1"
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==6272==
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==6272== Lock at 0x30A080 was first observed
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==6272== at 0x4C3403C: ??? (in /usr/lib/valgrind/vgpreload_helgrind-amd64-linux.so)
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==6272== by 0x108AD7: Pthread_mutex_lock (mythreads.h:23)
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==6272== by 0x108CF8: worker (main-deadlock.c:11)
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==6272== by 0x4C36C26: ??? (in /usr/lib/valgrind/vgpreload_helgrind-amd64-linux.so)
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==6272== by 0x4E496DA: start_thread (pthread_create.c:463)
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==6272== by 0x518288E: clone (clone.S:95)
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==6272== Address 0x30a080 is 0 bytes inside data symbol "m2"
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...
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```
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helgrind сообщает, что блокировка мьютексов происходит в неправильном порядке.
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## Задание 4
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Команда запуска:
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`valgrind --tool=helgrind ./lab9_main-deadlock-global_run`
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Результат:
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```text
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...
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==7133== Thread #3: lock order "0x30A080 before 0x30A0C0" violated
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==7133==
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==7133== Observed (incorrect) order is: acquisition of lock at 0x30A0C0
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==7133== at 0x4C3403C: ??? (in /usr/lib/valgrind/vgpreload_helgrind-amd64-linux.so)
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==7133== by 0x108AD7: Pthread_mutex_lock (mythreads.h:23)
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==7133== by 0x108D12: worker (main-deadlock-global.c:15)
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==7133== by 0x4C36C26: ??? (in /usr/lib/valgrind/vgpreload_helgrind-amd64-linux.so)
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==7133== by 0x4E496DA: start_thread (pthread_create.c:463)
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==7133== by 0x518288E: clone (clone.S:95)
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==7133==
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==7133== followed by a later acquisition of lock at 0x30A080
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==7133== at 0x4C3403C: ??? (in /usr/lib/valgrind/vgpreload_helgrind-amd64-linux.so)
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==7133== by 0x108AD7: Pthread_mutex_lock (mythreads.h:23)
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==7133== by 0x108D1E: worker (main-deadlock-global.c:16)
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==7133== by 0x4C36C26: ??? (in /usr/lib/valgrind/vgpreload_helgrind-amd64-linux.so)
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==7133== by 0x4E496DA: start_thread (pthread_create.c:463)
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==7133== by 0x518288E: clone (clone.S:95)
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==7133==
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==7133== Required order was established by acquisition of lock at 0x30A080
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==7133== at 0x4C3403C: ??? (in /usr/lib/valgrind/vgpreload_helgrind-amd64-linux.so)
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==7133== by 0x108AD7: Pthread_mutex_lock (mythreads.h:23)
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==7133== by 0x108CF8: worker (main-deadlock-global.c:12)
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==7133== by 0x4C36C26: ??? (in /usr/lib/valgrind/vgpreload_helgrind-amd64-linux.so)
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==7133== by 0x4E496DA: start_thread (pthread_create.c:463)
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==7133== by 0x518288E: clone (clone.S:95)
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==7133==
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==7133== followed by a later acquisition of lock at 0x30A0C0
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==7133== at 0x4C3403C: ??? (in /usr/lib/valgrind/vgpreload_helgrind-amd64-linux.so)
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==7133== by 0x108AD7: Pthread_mutex_lock (mythreads.h:23)
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==7133== by 0x108D04: worker (main-deadlock-global.c:13)
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==7133== by 0x4C36C26: ??? (in /usr/lib/valgrind/vgpreload_helgrind-amd64-linux.so)
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==7133== by 0x4E496DA: start_thread (pthread_create.c:463)
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==7133== by 0x518288E: clone (clone.S:95)
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==7133==
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==7133== Lock at 0x30A080 was first observed
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==7133== at 0x4C3403C: ??? (in /usr/lib/valgrind/vgpreload_helgrind-amd64-linux.so)
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==7133== by 0x108AD7: Pthread_mutex_lock (mythreads.h:23)
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==7133== by 0x108CF8: worker (main-deadlock-global.c:12)
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==7133== by 0x4C36C26: ??? (in /usr/lib/valgrind/vgpreload_helgrind-amd64-linux.so)
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==7133== by 0x4E496DA: start_thread (pthread_create.c:463)
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==7133== by 0x518288E: clone (clone.S:95)
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==7133== Address 0x30a080 is 0 bytes inside data symbol "m1"
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==7133==
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==7133== Lock at 0x30A0C0 was first observed
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==7133== at 0x4C3403C: ??? (in /usr/lib/valgrind/vgpreload_helgrind-amd64-linux.so)
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==7133== by 0x108AD7: Pthread_mutex_lock (mythreads.h:23)
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==7133== by 0x108D04: worker (main-deadlock-global.c:13)
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==7133== by 0x4C36C26: ??? (in /usr/lib/valgrind/vgpreload_helgrind-amd64-linux.so)
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==7133== by 0x4E496DA: start_thread (pthread_create.c:463)
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==7133== by 0x518288E: clone (clone.S:95)
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==7133== Address 0x30a0c0 is 0 bytes inside data symbol "m2"
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...
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```
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helgrind сообщает об аналогичной ошибке 3 заданию, тогда как она отсутствует, так как дополнительный мьютекс не допускает такую ситуацию.
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## Задание 5
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Команда запуска:
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`valgrind --tool=helgrind ./lab9_main-signal_run`
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Результат:
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```text
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...
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==7499== Possible data race during write of size 4 at 0x30A014 by thread #2
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==7499== Locks held: none
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==7499== at 0x108D36: worker (main-signal.c:9)
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==7499== by 0x4C36C26: ??? (in /usr/lib/valgrind/vgpreload_helgrind-amd64-linux.so)
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==7499== by 0x4E496DA: start_thread (pthread_create.c:463)
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==7499== by 0x518288E: clone (clone.S:95)
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==7499==
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==7499== This conflicts with a previous read of size 4 by thread #1
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==7499== Locks held: none
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==7499== at 0x108D83: main (main-signal.c:16)
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==7499== Address 0x30a014 is 0 bytes inside data symbol "done"
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...
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```
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helgrind сообщает о возможном одновременном использовании переменной done.
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Такой метод ожидания потока не является эффективным, так как:
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- может наступить чтение в момент записи
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- требует дополнительных затрат ожидающего потока.
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Наиболее эффективно было бы использовать мьютексы.
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## Задание 6
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Команда запуска:
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`valgrind --tool=helgrind ./lab9_main-signal-cv_run`
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Результат:
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```text
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...
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==9132== ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 7 from 7)
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...
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```
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helgrind не удалось обнаружить ошибок.
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По сравнению с прошлой программой данная более эффективна, так как она не производит постоянный опрос,
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а ожидает возвращение cond, и более безопасна для данных.
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