{"id":1820,"date":"2010-10-21T11:25:29","date_gmt":"2010-10-21T03:25:29","guid":{"rendered":"http:\/\/edsionte.com\/techblog\/?p=1820"},"modified":"2010-10-24T18:43:03","modified_gmt":"2010-10-24T10:43:03","slug":"%e5%86%85%e6%a0%b8%e5%90%8c%e6%ad%a5%e6%96%b9%e6%b3%95-%e8%87%aa%e6%97%8b%e9%94%81","status":"publish","type":"post","link":"http:\/\/edsionte.com\/techblog\/archives\/1820","title":{"rendered":"\u5185\u6838\u540c\u6b65\u65b9\u6cd5-\u9501\u673a\u5236"},"content":{"rendered":"

\u672c\u6587\u5c06\u4e3a\u4f60\u4ecb\u7ecd\u5185\u6838\u540c\u6b65\u7b97\u6cd5\u4e2d\u7684\u81ea\u65cb\u9501\u548c\u4fe1\u53f7\u91cf\u3002\u5728\u8fd9\u4e4b\u524d\uff0c\u5148\u4e86\u89e3\u4e00\u4e9b\u6982\u5ff5\u3002<\/p>\n

\u6267\u884c\u7ebf\u7a0b\uff1athread of execution\uff0c\u6307\u4efb\u4f55\u6b63\u5728\u6267\u884c\u7684\u4ee3\u7801\u5b9e\u4f8b\uff0c\u53ef\u80fd\u662f\u4e00\u4e2a\u6b63\u5728\u5185\u6838\u7ebf\u7a0b\uff0c\u4e00\u4e2a\u4e2d\u65ad\u5904\u7406\u7a0b\u5e8f\u7b49\u3002\u6709\u65f6\u5019\u4f1a\u5c06\u6267\u884c\u7ebf\u7a0b\u7b80\u79f0\u4e3a\u7ebf\u7a0b\u3002<\/p>\n

\u4e34\u754c\u533a\uff1acritical region\uff0c\u5373\u8bbf\u95ee\u548c\u64cd\u4f5c\u5171\u4eab\u6570\u636e\u7684\u4ee3\u7801\u6bb5\u3002<\/p>\n

\u591a\u4e2a\u6267\u884c\u7ebf\u7a0b\u5e76\u53d1\u8bbf\u95ee\u540c\u4e00\u8d44\u6e90\u901a\u5e38\u662f\u4e0d\u5b89\u5168\u7684\uff0c\u901a\u5e38\u4f7f\u7528\u81ea\u65cb\u9501\u548c\u4fe1\u53f7\u91cf\u6765\u5b9e\u73b0\u5bf9\u4e34\u754c\u533a\u4e92\u65a5\u7684\u8bbf\u95ee\u3002<\/p>\n

\u81ea\u65cb\u9501<\/h4>\n

\u81ea\u65cb\u9501(spin lock)\u662f\u4e00\u4e2a\u5bf9\u4e34\u754c\u8d44\u6e90\u8fdb\u884c\u4e92\u65a5\u8bbf\u95ee\u7684\u5178\u578b\u624b\u6bb5\u3002\u81ea\u65cb\u9501\u81f3\u591a\u53ea\u80fd\u88ab\u4e00\u4e2a\u6267\u884c\u7ebf\u7a0b\u6301\u6709\u3002\u5f53\u4e00\u4e2a\u6267\u884c\u7ebf\u7a0b\u60f3\u8981\u83b7\u5f97\u4e00\u4e2a\u5df2\u88ab\u4f7f\u7528\u7684\u81ea\u65cb\u9501\u65f6\uff0c\u8be5\u7ebf\u7a0b\u5c31\u4f1a\u4e00\u76f4\u8fdb\u884c\u5fd9\u7b49\u5f85\u76f4\u81f3\u8be5\u9501\u88ab\u91ca\u653e\uff0c\u5c31\u5982\u540c\u201c\u81ea\u65cb\u201d\u6240\u8868\u8fbe\u7684\u610f\u601d\u90a3\u6837\uff1a\u5728\u539f\u5730\u6253\u8f6c\u3002<\/p>\n

\u6211\u4eec\u4e5f\u53ef\u4ee5\u8fd9\u4e48\u7406\u89e3\u81ea\u65cb\u9501\uff1a\u5b83\u5982\u540c\u4e00\u628a\u95e8\u9501\uff0c\u800c\u4e34\u754c\u533a\u5c31\u5982\u540c\u95e8\u540e\u9762\u7684\u623f\u95f4\u3002\u5f53\u4e00\u4e2a\u7ebf\u7a0bA\u8fdb\u5165\u623f\u95f4\u540e\uff0c\u5b83\u4f1a\u5173\u95ed\u623f\u95e8\uff0c\u4f7f\u5f97\u5176\u4ed6\u7ebf\u7a0b\u4e0d\u5f97\u8fdb\u5165\u3002\u6b64\u65f6\u5982\u679c\u5176\u4ed6\u67d0\u4e2a\u8fdb\u7a0bB\u9700\u8981\u8fdb\u5165\u623f\u95f4\uff0c\u90a3\u4e48\u53ea\u80fd\u5728\u95e8\u5916\u201c\u6253\u8f6c\u201d\u3002\u5f53A\u8fdb\u7a0b\u6253\u5f00\u4eec\u540e\uff0c\u8fdb\u7a0bB\u624d\u80fd\u8fdb\u5165\u623f\u95f4\u3002<\/p>\n

\u81ea\u65cb\u9501\u7684\u4f7f\u7528<\/h4>\n

1.\u5b9a\u4e49\u521d\u59cb\u5316\u81ea\u65cb\u9501<\/p>\n

\u4f7f\u7528\u4e0b\u9762\u7684\u8bed\u53e5\u5c31\u53ef\u4ee5\u5148\u5b9a\u4e00\u4e2a\u81ea\u65cb\u9501\u53d8\u91cf\uff0c\u518d\u5bf9\u5176\u8fdb\u884c\u521d\u59cb\u5316\uff1a<\/p>\n

spinlock_t lock;\r\nspin_lock_init(&lock);<\/pre>\n
\u4e5f\u53ef\u4ee5\u8fd9\u6837\u521d\u59cb\u5316\u4e00\u4e2a\u81ea\u65cb\u9501\uff1a<\/p>\n
spinlock_t lock=SPIN_LOCK_UNLOCKED;<\/pre>\n
2.\u83b7\u5f97\u81ea\u65cb\u9501<\/p>\n
void spin_lock(spinlock_t*);\r\nint spin_trylock(spinlock_t*);<\/pre>\n
\u4f7f\u7528spin_lock(&lock)\u8fd9\u6837\u7684\u8bed\u53e5\u6765\u83b7\u5f97\u81ea\u65cb\u9501\u3002\u5982\u679c\u4e00\u4e2a\u7ebf\u7a0b\u53ef\u4ee5\u83b7\u5f97\u81ea\u65cb\u9501\uff0c\u5b83\u5c06\u9a6c\u4e0a\u8fd4\u56de\uff1b\u5426\u5219\uff0c\u5b83\u5c06\u81ea\u65cb\u81f3\u81ea\u65cb\u9501\u7684\u4fdd\u6301\u8005\u91ca\u653e\u9501\u3002<\/p>\n
\u53e6\u5916\u53ef\u4ee5\u4f7f\u7528spin_trylock(&lock)\u6765\u8bd5\u56fe\u83b7\u5f97\u81ea\u65cb\u9501\u3002\u5982\u679c\u4e00\u4e2a\u7ebf\u7a0b\u53ef\u4ee5\u7acb\u5373\u83b7\u5f97\u81ea\u65cb\u9501\uff0c\u5219\u8fd4\u56de\u771f\uff1b\u5426\u5219\uff0c\u8fd4\u56de\u5047\uff0c\u6b64\u65f6\u5b83\u5e76\u4e0d\u81ea\u65cb\u3002<\/p>\n
3.\u91ca\u653e\u81ea\u65cb\u9501<\/p>\n
void spin_unlock(spinlock_t*);<\/pre>\n
\u4f7f\u7528spin_unlock(&lock)\u6765\u91ca\u653e\u4e00\u4e2a\u5df2\u6301\u6709\u7684\u81ea\u65cb\u9501\u3002\u6ce8\u610f\u8fd9\u4e2a\u51fd\u6570\u5fc5\u987b\u548cspin_lock\u6216spin_trylock\u51fd\u6570\u914d\u5957\u4f7f\u7528\u3002<\/p>\n
\u5173\u4e8e\u81ea\u65cb\u9501\u7684\u8bf4\u660e<\/h4>\n
1.\u4fdd\u62a4\u6570\u636e\u3002\u6211\u4eec\u4f7f\u7528\u9501\u7684\u76ee\u7684\u662f\u4fdd\u62a4\u4e34\u754c\u533a\u7684\u6570\u636e\u800c\u4e0d\u662f\u4e34\u754c\u533a\u7684\u4ee3\u7801\u3002
\n2.\u5728\u4f7f\u7528\u81ea\u65cb\u9501\u65f6\u5019\uff0c\u5fc5\u987b\u5173\u95ed\u672c\u5730\u4e2d\u65ad\uff0c\u5426\u5219\u53ef\u80fd\u51fa\u73b0\u53cc\u91cd\u8bf7\u6c42\u7684\u6b7b\u9501\u3002\u6bd4\u5982\uff0c\u4e2d\u65ad\u5904\u7406\u7a0b\u5e8f\u6253\u65ad\u6b63\u6301\u6709\u81ea\u65cb\u9501\u7684\u5185\u6838\u4ee3\u7801\uff0c\u5982\u679c\u8fd9\u4e2a\u4e2d\u65ad\u5904\u7406\u7a0b\u5e8f\u53c8\u9700\u8981\u8fd9\u4e2a\u81ea\u65cb\u9501\uff0c\u90a3\u4e48\u8fd9\u4e2a\u4e2d\u65ad\u5904\u7406\u7a0b\u5e8f\u5c31\u4f1a\u81ea\u65cb\u7b49\u5f85\u81ea\u65cb\u9501\u88ab\u91ca\u653e\uff1b\u4f46\u662f\u8fd9\u4e2a\u9501\u7684\u6301\u6709\u8005\u6b64\u523b\u88ab\u4e2d\u65ad\u6253\u65ad\uff0c\u56e0\u6b64\u4e0d\u53ef\u80fd\u5728\u4e2d\u65ad\u5b8c\u6bd5\u4e4b\u524d\u91ca\u653e\u9501\u3002\u6b64\u65f6\u5c31\u51fa\u73b0\u4e86\u6b7b\u9501\u3002
\n3.\u81ea\u65cb\u9501\u662f\u5fd9\u7b49\u9501\u3002\u6b63\u5982\u540c\u524d\u9762\u6240\u8bf4\u7684\u90a3\u6837\uff0c\u5f53\u5176\u4ed6\u7ebf\u7a0b\u6301\u6709\u81ea\u65cb\u9501\u65f6\uff0c\u5982\u679c\u53e6\u6709\u7ebf\u7a0b\u60f3\u83b7\u5f97\u8be5\u9501\uff0c\u90a3\u4e48\u5c31\u53ea\u80fd\u5faa\u73af\u7684\u7b49\u5f85\u3002\u8fd9\u6837\u5fd9\u7684\u529f\u80fd\u5bf9CPU\u6765\u8bf4\u662f\u6781\u5927\u7684\u6d6a\u8d39\u3002\u56e0\u6b64\u53ea\u6709\u5f53\u7531\u81ea\u65cb\u9501\u4fdd\u62a4\u7684\u4e34\u754c\u533a\u6267\u884c\u65f6\u95f4\u5f88\u77ed\u65f6\uff0c\u4f7f\u7528\u81ea\u65cb\u9501\u624d\u6bd4\u8f83\u5408\u7406\u3002
\n4.\u81ea\u65cb\u9501\u4e0d\u80fd\u9012\u5f52\u4f7f\u7528\u3002\u8fd9\u4e00\u70b9\u4e5f\u5f88\u597d\u7406\u89e3\uff0c\u5982\u679c\u5f53\u524d\u6301\u6709\u9501\u7684\u7ebf\u7a0b\u53c8\u9700\u8981\u518d\u6301\u6709\u8be5\u9501\uff0c\u90a3\u4e48\u5b83\u5fc5\u987b\u81ea\u65cb\uff0c\u7b49\u5f85\u9501\u88ab\u91ca\u653e\uff1b\u4f46\u662f\u8fd9\u4e2a\u9501\u672c\u8eab\u53c8\u88ab\u5b83\u81ea\u5df1\u6301\u6709\uff0c\u56e0\u6b64\u8fd9\u4e2a\u7ebf\u7a0b\u6c38\u8fdc\u65e0\u6cd5\u7ee7\u7eed\u5411\u524d\u63a8\u8fdb\u3002<\/p>\n
\u4fe1\u53f7\u91cf<\/h4>\n
\u4fe1\u53f7\u91cf\uff08semaphore\uff09\u662f\u4fdd\u62a4\u4e34\u754c\u533a\u7684\u4e00\u79cd\u5e38\u7528\u65b9\u6cd5\u3002\u5b83\u7684\u529f\u80fd\u4e0e\u81ea\u65cb\u9501\u76f8\u540c\uff0c\u53ea\u80fd\u5728\u5f97\u5230\u4fe1\u53f7\u91cf\u7684\u8fdb\u7a0b\u624d\u80fd\u6267\u884c\u4e34\u754c\u533a\u7684\u4ee3\u7801\u3002\u4f46\u662f\u548c\u81ea\u65cb\u9501\u4e0d\u540c\u7684\u662f\uff0c\u4e00\u4e2a\u8fdb\u7a0b\u4e0d\u80fd\u83b7\u5f97\u4fe1\u53f7\u91cf\u65f6\uff0c\u5b83\u4f1a\u8fdb\u5165\u7761\u7720\u72b6\u6001\u800c\u4e0d\u662f\u81ea\u65cb\u3002<\/p>\n
\u5229\u7528\u4e0a\u8ff0\u81ea\u65cb\u9501\u7684\u95e8\u548c\u9501\u7684\u4f8b\u5b50\uff0c\u6211\u4eec\u53ef\u4ee5\u8fd9\u6837\u89e3\u91ca\u4fe1\u53f7\u91cf\u3002\u6211\u4eec\u5c06\u4fe1\u53f7\u91cf\u6bd4\u4f5c\u94a5\u5319\u3002\u8fdb\u7a0bA\u60f3\u8981\u8fdb\u5165\u623f\u95f4\uff0c\u5c31\u5fc5\u8981\u6301\u6709\u4e00\u628a\u94a5\u5319\u3002\u5f53\u94a5\u5319\u88ab\u4f7f\u7528\u5b8c\u4e4b\u540e\uff0c\u5982\u679c\u53c8\u6709\u8fdb\u7a0bB\u60f3\u8fdb\u623f\u95f4\uff0c\u90a3\u4e48\u8fd9\u4e2a\u8fdb\u7a0b\u5728\u7b49\u5f85\u5176\u4ed6\u8fdb\u7a0b\u4ece\u623f\u95f4\u51fa\u6765\u7ed9\u5b83\u94a5\u5319\u7684\u540c\u65f6\u4f1a\u6253\u76f9\u3002\u5f53\u623f\u95f4\u91cc\u7684\u67d0\u4e2a\u8fdb\u7a0b\u51fa\u6765\u65f6\u4f1a\u6447\u9192\u8fd9\u4e2a\u7761\u89c9\u7684\u8fdb\u7a0bB\u3002<\/p>\n
\u4fe1\u53f7\u91cf\u7684\u4f7f\u7528<\/h4>\n
0.\u6570\u636e\u7ed3\u6784<\/p>\n
  16struct semaphore {\r\n  17        spinlock_t              lock;\r\n  18        unsigned int            count;\r\n  19        struct list_head        wait_list;\r\n  20};<\/pre>\n
count\uff1a\u521d\u59cb\u5316\u4fe1\u53f7\u91cf\u65f6\u6240\u8bbe\u7f6e\u7684\u4fe1\u53f7\u91cf\u503c\u3002
\nwait_list\uff1a\u7b49\u5f85\u961f\u5217\uff0c\u8be5\u961f\u5217\u4e2d\u5373\u4e3a\u7b49\u5f85\u4fe1\u53f7\u91cf\u7684\u8fdb\u7a0b\u3002
\nlock\uff1a\u81ea\u65cb\u9501\u53d8\u91cf<\/p>\n
1.\u5b9a\u4e49\u521d\u59cb\u5316\u4fe1\u53f7\u91cf<\/p>\n
\u4f7f\u7528\u4e0b\u9762\u7684\u4ee3\u7801\u53ef\u4ee5\u5b9a\u4e49\u5e76\u521d\u59cb\u5316\u4fe1\u53f7\u91cfsem\uff1a<\/p>\n
struct semaphore sem;
\nsem_init(&sem,val);<\/p>\n
\u5176\u4e2dval\u5373\u4e3a\u4fe1\u53f7\u91cf\u7684\u521d\u59cb\u503c\u3002<\/p>\n
\u5982\u679c\u6211\u4eec\u60f3\u4f7f\u7528\u4e92\u65a5\u4fe1\u53f7\u91cf\uff0c\u5219\u4f7f\u7528\u4e0b\u9762\u7684\u51fd\u6570\uff1a<\/p>\n
init_MUTEX(&sem);<\/p>\n
\u8fd9\u4e2a\u51fd\u6570\u4f1a\u5c06sem\u7684\u503c\u521d\u59cb\u4e3a1\uff0c\u5373\u7b49\u540c\u4e8esem_init(&sem,1);<\/p>\n
\u5982\u679c\u60f3\u5c06\u4e92\u65a5\u4fe1\u53f7\u91cf\u7684\u521d\u503c\u8bbe\u4e3a0\uff0c\u5219\u53ef\u4ee5\u76f4\u63a5\u4f7f\u7528\u4e0b\u9762\u7684\u51fd\u6570\uff1a<\/p>\n
init_MUTEX_LOCKED(&sem);<\/p>\n
\u9664\u4e0a\u9762\u7684\u65b9\u6cd5\uff0c\u53ef\u4ee5\u4f7f\u7528\u4e0b\u9762\u7684\u4e24\u4e2a\u5b8f\u5b9a\u4e49\u5e76\u521d\u59cb\u5316\u4fe1\u53f7\u91cf\uff1a<\/p>\n
DECLARE_MUTEX(name);<\/p>\n
DECLARE_MUTEX_LOCKED(name);<\/p>\n
\u5176\u4e2dname\u4e3a\u53d8\u91cf\u540d\u3002<\/p>\n
2.\u83b7\u5f97\u4fe1\u53f7\u91cf<\/p>\n
down(&sem);<\/p>\n
\u8fdb\u7a0b\u4f7f\u7528\u8be5\u51fd\u6570\u65f6\uff0c\u5982\u679c\u4fe1\u53f7\u91cf\u503c\u6b64\u65f6\u4e3a0\uff0c\u5219\u8be5\u8fdb\u8f66\u4f1a\u8fdb\u5165\u7761\u7720\u72b6\u6001\uff0c\u56e0\u6b64\u8be5\u51fd\u6570\u4e0d\u80fd\u7528\u4e8e\u4e2d\u65ad\u4e0a\u4e0b\u6587\u4e2d\u3002<\/p>\n
down_interruptibale(&sem);<\/p>\n
\u8be5\u51fd\u6570\u4e0edown\u51fd\u6570\u529f\u80fd\u7c7b\u4f3c\uff0c\u53ea\u4e0d\u8fc7\u4f7f\u7528down\u800c\u7761\u7720\u7684\u8fdb\u7a0b\u4e0d\u80fd\u88ab\u4fe1\u53f7\u6240\u6253\u65ad\uff0c\u800c\u4f7f\u7528down_interruptibale\u7684\u51fd\u6570\u5219\u53ef\u4ee5\u88ab\u4fe1\u53f7\u6253\u65ad\u3002<\/p>\n
\u5982\u679c\u60f3\u8981\u5728\u4e2d\u65ad\u4e0a\u4e0b\u6587\u4f7f\u7528\u4fe1\u53f7\u91cf\uff0c\u5219\u53ef\u4ee5\u4f7f\u7528\u4e0b\u9762\u7684\u51fd\u6570\uff1a<\/p>\n
dwon_try(&sem);<\/p>\n
\u4f7f\u7528\u8be5\u51fd\u6570\u65f6\uff0c\u5982\u679c\u8fdb\u7a0b\u53ef\u4ee5\u83b7\u5f97\u4fe1\u53f7\u91cf\uff0c\u5219\u8fd4\u56de0\uff1b\u5426\u5219\u8fd4\u56de\u975e0\u503c\uff0c\u4e0d\u4f1a\u5bfc\u81f4\u7761\u7720\u3002<\/p>\n
3.\u91ca\u653e\u4fe1\u53f7\u91cf<\/p>\n
up(&sem);<\/p>\n
\u8be5\u51fd\u6570\u4f1a\u91ca\u653e\u4fe1\u53f7\u91cf\uff0c\u5982\u679c\u6b64\u65f6\u7b49\u5f85\u961f\u5217\u4e2d\u6709\u8fdb\u7a0b\uff0c\u5219\u5524\u9192\u4e00\u4e2a\u3002<\/p>\n
\u4fe1\u53f7\u91cf\u7684\u540c\u6b65<\/h4>\n
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