Timer library in C [closed] - c

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I'm looking for an open source timer library written in C. The library should have Timer callback functions, etc.
On searching I see POSIX timers or setitimer(), which use a signal based approach that may lead to problems in multithreaded code.
Say if I use POSIX Timers inside threaded code, the signals won't be reaching to the correct place. If I use several timers in a process then each one should use different signals. Are there any other alternatives?

Answer 1

Since you are running Linux, I would recommend using the built in POSIX timer API's.
int timer_create(clockid_t clockid, struct sigevent *sevp, timer_t *timerid);
Here is a link to some documentation showing how to use POSIX timers which provide support for callback functions.
Regarding multiple timers in a process, the documentation says this:
A program may create multiple interval timers using timer_create().
Timers are not inherited by the child of a fork(2), and are disarmed and
deleted during an execve(2).
The kernel preallocates a "queued real-time signal" for each timer created
using timer_create(). Consequently, the number of timers is limited by the
RLIMIT_SIGPENDING resource limit (see setrlimit(2)).
Note that POSIX timers can be used in a threaded application by setting up notification using SIGEV_THREAD_ID as shown below:
The sevp.sigev_notify field can have the following values:
SIGEV_NONE
Don't asynchronously notify when the timer expires. Progress of the
timer can be monitored using timer_gettime(2).
SIGEV_SIGNAL
Upon timer expiration, generate the signal sigev_signo for the process.
See sigevent(7) for general details. The si_code field of the
siginfo_t structure will be set to SI_TIMER. At any point in time, at
most one signal is queued to the process for a given timer; see
timer_getoverrun(2) for more details.
SIGEV_THREAD
Upon timer expiration, invoke sigev_notify_function as if it were the
start function of a new thread. See sigevent(7) for details.
SIGEV_THREAD_ID (Linux-specific)
As for SIGEV_SIGNAL, but the signal is targeted at the thread whose ID
is given in sigev_notify_thread_id, which must be a thread in the same
process as the caller. The sigev_notify_thread_id field specifies a
kernel thread ID, that is, the value returned by clone(2) or gettid(2).
This flag is only intended for use by threading libraries.

Answer 2

The Linux way of doing it would be via timerfd_create which integrates nicely with epoll-based event loops (and thereby avoiding the restrictions of signal handlers)

Answer 3

This is far to simple to create a library for.
example:
#include <time.h>
int main()
{
time_t start,end;
double dif;
double duration=40f; //duration of timer
bool loop=true;
while(loop==true)
{
time(&start);
if(dif==duration)
{
/*callback*/
dif=0;
}
//do stuff
time(&end);
dif+=difftime(end,start);
}
{