Linux信号实践(5) --时间与定时器

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