How does nanosleep work?

How does nanosleep work?

The nanosleep() function shall cause the current thread to be suspended from execution until either the time interval specified by the rqtp argument has elapsed or a signal is delivered to the calling thread, and its action is to invoke a signal-catching function or to terminate the process.

What is hrtimer linux?

The hrtimer code provides a function for advancing the expiration time to the next such interval: unsigned long hrtimer_forward(struct hrtimer *timer, ktime_t interval); This function will advance the timer’s expiration time by the given interval.

How accurate is Nanosleep?

However, because of the details of how the Linux kernel works, the actual precision provided by nanosleep is 10 milliseconds—still better than that afforded by sleep. This additional precision can be useful, for instance, to schedule frequent operations with short time intervals between them.

What is jiffies in kernel?

The global variable “jiffies” holds the number of ticks that have occurred since the system booted. On boot, the kernel initializes the variable to zero, and it is incremented by one during each timer interrupt. Thus, because there are HZ timer interrupts in a second, there are HZ jiffies in a second.

How do you implement Nanosleep?

The typical way to implement sleep() and nanosleep() is to convert the argument into whatever scale the OS’s scheduler uses (while rounding up) and add the current time to it to form an “absolute wake up time”; then tell the scheduler not to give the thread CPU time until after that “absolute wake up time” has been …

What does Nanosleep mean?

DESCRIPTION top. nanosleep() suspends the execution of the calling thread until either at least the time specified in *req has elapsed, or the delivery of a signal that triggers the invocation of a handler in the calling thread or that terminates the process.

What is Clock_monotonic?

CLOCK_MONOTONIC A nonsettable system-wide clock that represents monotonic time since—as described by POSIX—”some unspecified point in the past”. On Linux, that point corresponds to the number of seconds that the system has been running since it was booted.

How long is a jiffy kernel?

1 ms
It is not an absolute time interval unit, since its duration depends on the clock interrupt frequency of the particular hardware platform under review. Within the Linux 2.6 operating system kernel, on the Intel i386 platform, a jiffie is 1 ms, or 1/1000th of a second. It is different on other hardware platforms.

Is Nanosleep thread safe?

No, only the “current” thread is suspended. nanosleep() suspends the execution of the calling thread until either at least the time specified in *req has elapsed, or the delivery of a signal that triggers the invocation of a handler in the calling thread or that terminates the process.

Is Clock_gettime a system call?

Clock_gettime. The clock_gettime system call is a successor to the gettimeofday system call with a few key changes: higher precision and the ability to request specific clocks. It fills in a structure containing two fields: a seconds and a nanosecond count of the time since the Epoch (00:00 1 January, 1970 UTC).

What is the relationship between hrtimer _ nanosleep and clock?

This points to common_nsleepwhich is a wrapper around hrtimer_nanosleep. That’s the relationship between the two: clock_nanosleepis a system call, and hrtimer_nanosleepis the internal kernel function used to implement it. You can’t call the latter from outside the kernel, only the former.

What does nanosleep do to the calling thread?

nanosleep() suspends the execution of the calling thread until either at least the time specified in *req has elapsed, or the delivery of a signal that triggers the invocation of a handler in the calling thread or that terminates the process.

When was nanosleep removed from the Linux kernel?

This special extension was removed in kernel 2.5.39, and is thus not available in Linux 2.6.0 and later kernels.

What happens when nanosleep is interrupted by a signal handler?

If the call is interrupted by a signal handler, nanosleep () returns -1, sets errno to EINTR, and writes the remaining time into the structure pointed to by rem unless rem is NULL. The value of *rem can then be used to call nanosleep () again and complete the specified pause (but see NOTES).