三种不同精度的睡眠
1.sleep
#include <unistd.h>
unsigned int sleep(unsigned int seconds);
RETURN VALUE
Zero if the requested time has elapsed, or the number of seconds left to sleep,
if the call was interrupted by a signal handler.
//示例int sleepTime = 5;do{ sleepTime = sleep(sleepTime);}while (sleepTime > 0);
2.usleep(以微秒为单位)
int usleep(useconds_t usec);
The type useconds_t is an unsigned integer type capable of holding integers in the range [0,1000000].
Programs will be more portable if they never mention this type explicitly.
3.nanosleep(以纳秒为单位)
#include <time.h>int nanosleep(const struct timespec *req, struct timespec *rem);
req指定睡眠的时间, rem返回剩余的睡眠时间
struct timespec{ time_t tv_sec; /* seconds: 秒 */ long tv_nsec; /* nanoseconds: 纳秒 */};
三种时间结构
time_t
struct timeval {long tv_sec; /* seconds */long tv_usec; /* microseconds 微秒*/};
struct timespec {time_t tv_sec; /* seconds */long tv_nsec; /* nanoseconds */};
setitimer
#include <sys/time.h>int setitimer(int which, const struct itimerval *value, struct itimerval *ovalue));
setitimer()比alarm功能强大，支持3种类型的定时器
参数
第一个参数which指定定时器类型
第二个参数是请求的时间
第三个参数是定时器原来所关联的值
struct itimerval{ struct timeval it_interval; /* next value : 产生信号的间隔时间*/ struct timeval it_value; /* current value : 第一次产生信号的时间*/};struct timeval{ time_t tv_sec; /* seconds: 秒 */ suseconds_t tv_usec; /* microseconds: 微秒 */};
which值
ITIMER_REAL：经过指定的时间后，内核将发送SIGALRM信号给本进程 (用的较多)
ITIMER_VIRTUAL ：程序在用户空间执行指定的时间后，内核将发送SIGVTALRM信号给本进程
ITIMER_PROF ：进程在内核空间中执行时，时间计数会减少，通常与ITIMER_VIRTUAL共用，代表进程在用户空间与内核空间中运行指定时间后，内核将发送SIGPROF信号给本进程。
/**示例1:1.在启动进程的5秒之后产生信号2.然后每隔1秒产生一次信号**/int main(){ if (signal(SIGALRM, signalAction) == SIG_ERR) err_exit("signal error"); struct itimerval it; struct timeval it_interval = {1, 0}; struct timeval it_value = {5, 0}; it.it_interval = it_interval; it.it_value = it_value; if (setitimer(ITIMER_REAL, &it, NULL) == -1) err_exit("setitimer error"); while (true) pause();}
/**示例2:获取itimerval 结构体**/int main(){ struct itimerval it; struct timeval it_interval = {1, 0}; struct timeval it_value = {5, 0}; it.it_interval = it_interval; it.it_value = it_value; if (setitimer(ITIMER_REAL, &it, NULL) == -1) err_exit("setitimer error"); for (int i = 0; i < 100000; ++i) ; struct itimerval oldIt;// if (setitimer(ITIMER_REAL, &it, &oldIt) == -1)// err_exit("setitimer error"); // 在不重新设置时钟的情况下获取剩余时间 if (getitimer(ITIMER_REAL, &oldIt) == -1) err_exit("getitimer error"); cout << oldIt.it_interval.tv_sec << ' ' << oldIt.it_interval.tv_usec << ' ' << oldIt.it_value.tv_sec << ' ' << oldIt.it_value.tv_usec << endl;}
附:秒-微秒-纳秒的转换
S(秒)、ms(毫秒)、μs(微秒)、ns(纳秒)，其中：1s=1000ms，1 ms=1000μs，1μs=1000ns