/*
* Structure returned by gettimeofday(2) system call,
* and used in other calls.
*/
系统时间timeval的结构由2部分组成，一部分是秒tv_sec，另一个部分是微秒tv_usec;
struct timeval {
time_t tv_sec; /* seconds */
suseconds_t tv_usec; /* and microseconds */
};
本博客所有内容是原创，如果转载请注明来源
http://blog.csdn.net/myhaspl/
POSIX.1b定义了另一个类似于timeval的系统时间结构纳秒
POSIX 标准的实时部分(POSIX.1b)，POSIX.1b-1993标准详细定义了UNIX系统中关于实时性的特征。在标准中主要定义了调度的优先权，内存锁，实时信号，改良的IPC和定时器和一些其他的功能。
POSIX.1b-1993 defines in addition to POSIX.1-1990 the following new
concepts and functions:
Improved Signals
----------------
POSIX.1b adds a new class of signals. These have the following new
features:
- there are much more user specified signals now, not only SIGUSR1
and SIGUSR2.
- The additional POSIX.1b signals can now carry a little bit data (a
pointer or an integer value) that can be used to transfer to the
signal handler information about why the signal has been caused.
- The new signals are queued, which means that if several signals of
the same type arrive before the signal handler is called, all of
them will be delivered.
- POSIX.1b signals have a well-defined delivery order, i.e. you can
work now with signal priorities.
- A new function sigwaitinfo() allows to wait on signals and to
continue quickly after the signal arrived with program execution
without the overhead of calling a signal handler first.
The new queued signals are a necessary prerequisite for the
implementation of the POSIX.1b asynchronous I/O interface (see below).
They might also provide a good interface for delivering hardware
interrupts to user processes.
New functions for signals are:
sigwaitinfo(), sigtimedwait(), sigqueue().
由2部分组成，一部分是秒 tv_sec，另一个部分是纳秒（十亿分之一秒）tv_nsec
/*
* Structure defined by POSIX.1b to be like a timeval.
*/
struct timespec {
time_t tv_sec; /* seconds */
long tv_nsec; /* and nanoseconds */
};
需要有一个操作完成这2种格式的转换
#if defined(_NETBSD_SOURCE)
系统时间转实时扩展标准
#define TIMEVAL_TO_TIMESPEC(tv, ts) do { \
(ts)->tv_sec = (tv)->tv_sec; \
(ts)->tv_nsec = (tv)->tv_usec * 1000; \
} while (/*CONSTCOND*/0)
上面主要是操作微秒部分，因为要将其转为纳秒，下面是类似的操作，将纳秒转为微秒。
1纳秒 =0.001
微秒
#define TIMESPEC_TO_TIMEVAL(tv, ts) do { \
(tv)->tv_sec = (ts)->tv_sec; \
(tv)->tv_usec = (suseconds_t)(ts)->tv_nsec / 1000; \
} while (/*CONSTCOND*/0)
只所以这么写
do
{
..
}while(/*...*/0)
第一，源代码只循环一次，
第二，可以加上灵活的条件，在什么情况下再重新尝试一次
或者可以加上灵活的条件，在什么情况下再重新尝试一次
接下来是时区
struct timezone {
int tz_minuteswest; /* minutes west of Greenwich */
int tz_dsttime; /* type of dst correction */
};
时区已经不再用了，为提供向后兼容性，保留下来