原文網址：http://blog.csdn.net/hongszh/article/details/8608781

最強大的定時器接口來自POSIX時鐘系列，其創建、初始化以及刪除一個定時器的行動被分為三個不同的函數：timer_create()(創建定時器)、timer_settime()(初始化定時器)以及timer_delete(銷毀它)。

man timer_create/timer_settime，可以看到man幫助的詳細文檔：

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TIMER_CREATE(2)??????????????????????????????????????Linux?Programmer's?Manual????

??

NAME??

???????timer_create?-?create?a?POSIX?per-process?timer??

??

SYNOPSIS??

???????#include?<signal.h>??

???????#include?<time.h>??

??

???????int?timer_create(clockid_t?clockid,?struct?sigevent?*sevp,??

????????????????????????timer_t?*timerid);??

???????int?timer_settime(timer_t?timerid,?int?flags,??

?????????????????????????const?struct?itimerspec?*new_value,??

?????????????????????????struct?itimerspec?*?old_value);??

???????int?timer_gettime(timer_t?timerid,?struct?itimerspec?*curr_value);??

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我的實現如下：

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1. 定義timer timeout的函數指針類型：?

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typedef?void?(*timerTimeout)(union?sigval?sig);??

2. 為我們的GstPlayer定義兩個timer ID：

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timer_t??mSeekTimer;??

timer_t??mPrepareAsyncTimer;??

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3. 定義createTimer函數，創建timer，設置timeout函數
? ? timerId: 輸入輸出參數
? ? func: ? ?timer timeout函數

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void?createTimer(timer_t?*timerId,?timerTimeout?func)??

{??

????struct?sigevent?sev;??

??

????sev.sigev_notify?=?SIGEV_THREAD;??

????sev.sigev_signo?=?SIGRTMIN;??

????sev.sigev_value.sival_ptr?=?gPlayer;??

????sev.sigev_notify_function?=?func;??

????sev.sigev_notify_attributes?=?NULL;??

??

????/*?create?timer?*/??

????if?(timer_create?(CLOCK_REALTIME,?&sev,?timerId)?==?-1)??

????{??

????????ERR?("timer_create,?error");??

????????return;??

????}??

??

????if?(*timerId?==?-1)??

????????ERR??("timer_create?error,?id?is?-1");??

????return;??

}??

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4. setTimer函數, 調用linux的timer_settime, 如果還沒到time out，重置之前的timer

?

如果已經time out，那就得重新調用createTimer生成有效的timer ID，然后才能調用setTimer開始定時器計時。

-這里，將interval參數設置為0，指定我的定時器不工作在循環模式。
-timeMSec是輸入參數，指定time out的時間，單位為毫秒。

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void?setTimer(timer_t?*timerId,?int?timeMSec)??

{??

????struct?itimerspec?its;??

??

????/*?Start?the?timer?*/??

????its.it_value.tv_sec?=?timeMSec?/?1000;??

????its.it_value.tv_nsec?=?(timeMSec?%?1000)?*?1000000;??

??

????its.it_interval.tv_sec?=?0;??

????its.it_interval.tv_nsec?=?0;??

??

????if?(timer_settime?(*timerId,?0,?&its,?NULL)?==?-1)??

????{??

????????ERR?("timer_settime?error");??

????}??

????DEBUG?("call?timer_settime?reset?timer?done.");??

????return;??

}??

?

seekTimerTimeout函數，time out以后，銷毀之前調用createTimer創建的timer，完成time out后要做的工作

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void?seekTimerTimeout(union?sigval?sig)??

{??

????GstPlayer?*player?=?(GstPlayerplayer*)sig.sival_ptr;??

????if?(player->mSeekTimer?!=?-1)??

????{??

????????DEBUG("timeout,?delete?timer:Id?=?%d",??

????????????????player->mSeekTimer);??

????????timer_delete(player->mSeekTimer);??

????????player->mSeekTimer?=?-1;??

????}??

????//?...?完成time?out后要做的工作??

}??

prepareAsyncTimeout的time out函數：

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void?prepareAsyncTimeout(union?sigval?sig)??

{??

????GstStateChangeReturn?state_return;??

????GstPlayer?*player?=?(GstPlayerplayer*)sig.sival_ptr;??

??

????if?(player->mPrepareAsyncTimer?!=?-1)??

????{??

????????DEBUG("timeout,?delete?timer:Id?=?%d",??

????????????????player->mPrepareAsyncTimer);??

????????timer_delete(player->mPrepareAsyncTimer);??

????????player->mPrepareAsyncTimer?=?-1;??

????}??

??

????//?...完成time?out后要做的工作??

}??

調用一：

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創建timer，設定prepareAsyncTimeout??

開始timer，timeout時間為500ms??

??

????????createTimer(&mPrepareAsyncTimer,?prepareAsyncTimeout);??

????????setTimer(&mPrepareAsyncTimer,?500/*ms*/);??

調用二：?

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創建timer，設定timeout回調函數。??

????//?create?timer??

????if?(mSeekTimer?==?-1)??

????{??

????????createTimer(&mSeekTimer,?seekTimerTimeout);??

????}??

??

判斷mSeekTimer是否有效，有效，計算到timeout的剩余時間，如果還沒到timeout，重置timer，??

開始新的計時。??

????//?if?timer?exist?and?not?expire,?reset?timer.??

????if?(mSeekTimer?!=?-1)??

????{??

????????gulong?remaining?=?0;?//us??

????????struct?itimerspec?its;??

??

????????timer_gettime(mSeekTimer,?&its);??

????????remaining?=?its.it_value.tv_sec?*?1000000??

???????????????????its.it_value.tv_nsec?/?1000;??

????????DEBUG?("--?remaining?time?=?%lu?us",?remaining);??

????????if?((100/*ms*/?*?1000?-?remaining)?>?0)??

????????{??

???????????setTimer(&mSeekTimer,?100/*ms*/);??

???????????DEBUG?("the?new?seek?interval?<?100ms,?return");??

???????????mSeekCount?=?1;??

???????????return?TRUE;??

????????}??

????}??

?

參考：

http://blog.163.com/zheng_he_xiang/blog/static/18650532620116311020390/
http://blog.csdn.net/leo9150285/article/details/8271910

轉載于:https://www.cnblogs.com/wi100sh/p/4281618.html

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