[問題] multi-thread 共用函數的問題

看板C_and_CPP作者cris122 (總是很多心事)時間10年前 (2016/01/21 11:22)推噓6(6推 0噓 12→)

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開發平台(Platform): (Ex: VC++, GCC, Linux, ...) Linux 額外使用到的函數庫(Library Used): (Ex: OpenGL, ...) gcc pthread 問題(Question)：一般在 multithread 共用函數時會Lock，但請教在什麼情況下可以不用 Lock? 或者說在什麼情況下一定要 Lock? 寫了一個 sample 不 Lock 執行不會有錯誤程式碼(Code)：(請善用置底文網頁, 記得排版) #include <stdio.h> #include <stdlib.h> #include <pthread.h> #include <unistd.h> pthread_t thread_id_1 = 0; pthread_t thread_id_2 = 0; int sum = 0; void common(int x) { sum += x; } void thread_func_1() { int i; for (i = 0; i < 100; i++) { common(-1); } printf("thread1 end\n"); } void thread_func_2() { int i; for (i = 0; i < 100; i++) { common(1); } printf("thread2 end\n"); } void thread_create_1() { int rc = 0; rc = pthread_create(&thread_id_1, NULL, (void *) &thread_func_1, NULL); if (rc) { fprintf(stderr, "ERROR; return code from pthread_create() is %d\n", rc); return; } } void thread_create_2() { int rc = 0; rc = pthread_create(&thread_id_2, NULL, (void *) &thread_func_2, NULL); if (rc) { fprintf(stderr, "ERROR; return code from pthread_create() is %d\n", rc); return; } } void thread_wait_1() { if (thread_id_1 != 0) { pthread_join(thread_id_1, NULL); printf("thread 1 stopped\n"); } } void thread_wait_2() { if (thread_id_2 != 0) { pthread_join(thread_id_2, NULL); printf("thread 2 stopped\n"); } } int main(void) { thread_create_1(); thread_create_2(); thread_wait_1(); thread_wait_2(); printf("sum = %d\n", sum); return EXIT_SUCCESS; } -- ※ 發信站: 批踢踢實業坊(ptt.cc), 來自: 111.249.106.112 ※ 文章網址: https://www.ptt.cc/bbs/C_and_CPP/M.1453346562.A.A83.html

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