dispatch_semaphore_create(long value); // 創(chuàng)建信號量dispatch_semaphore_signal(dispatch_semaphore_t deem); // 發(fā)送信號量 信號量會加1，釋放資源，相當于解鎖

dispatch_semaphore_wait(dispatch_semaphore_t dsema, dispatch_time_t timeout); // 等待信號量，如果信號量為0則等待。否則往下執(zhí)行并且信號量減1.相當于加鎖

標準用法例子

dispatch_semaphore_t _semaphore =?dispatch_semaphore_create(1)

dispatch_semaphore_wait(_semaphore,DISPATCH_TIME_FOREVER)

需要加鎖的代碼

dispatch_semaphore_signal(_semaphore);?