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alarm signal processing
Post 302322931 by liaobert on Friday 5th of June 2009 01:39:05 AM
06-05-2009
alarm signal processing
I'm writing a function right now, and I want to set an alarm to avoid a timeout, here's the general idea of my code:
int amt = -2;
alarm(10);
amt = read(fd, &t->buf[tailpos], TASKBUFSIZ - tailpos); //do a read
when the alarm goes off, i want to check the value of "amt"
basically, i want to check to see that the read call was completed in under 10 seconds, however in a signal handler, i dont think you can pass in the value of amt. so is my approach possible to implement? or would i need to a fork a process and do it that way? I'd prefer not to do that, I ran into some problems with that approach..
here's the entirety of the function as well:
taskbufresult_t read_to_taskbuf(int fd, task_t *t)
{
unsigned headpos = (t->head % TASKBUFSIZ);
unsigned tailpos = (t->tail % TASKBUFSIZ);
ssize_t amt;
if (t->head == t->tail || headpos < tailpos)
amt = read(fd, &t->buf[tailpos], TASKBUFSIZ - tailpos);
else
amt = read(fd, &t->buf[tailpos], headpos - tailpos);
if (amt == -1 && (errno == EINTR || errno == EAGAIN
|| errno == EWOULDBLOCK))
return TBUF_AGAIN;
else if (amt == -1)
return TBUF_ERROR;
else if (amt == 0)
return TBUF_END;
else {
t->tail += amt;
return TBUF_OK;
}
}
help would be much appreciated, my TAs suck...
int amt = -2;
alarm(10);
amt = read(fd, &t->buf[tailpos], TASKBUFSIZ - tailpos); //do a read
when the alarm goes off, i want to check the value of "amt"
basically, i want to check to see that the read call was completed in under 10 seconds, however in a signal handler, i dont think you can pass in the value of amt. so is my approach possible to implement? or would i need to a fork a process and do it that way? I'd prefer not to do that, I ran into some problems with that approach..
here's the entirety of the function as well:
taskbufresult_t read_to_taskbuf(int fd, task_t *t)
{
unsigned headpos = (t->head % TASKBUFSIZ);
unsigned tailpos = (t->tail % TASKBUFSIZ);
ssize_t amt;
if (t->head == t->tail || headpos < tailpos)
amt = read(fd, &t->buf[tailpos], TASKBUFSIZ - tailpos);
else
amt = read(fd, &t->buf[tailpos], headpos - tailpos);
if (amt == -1 && (errno == EINTR || errno == EAGAIN
|| errno == EWOULDBLOCK))
return TBUF_AGAIN;
else if (amt == -1)
return TBUF_ERROR;
else if (amt == 0)
return TBUF_END;
else {
t->tail += amt;
return TBUF_OK;
}
}
help would be much appreciated, my TAs suck...
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LEARN ABOUT OSF1
alarm
alarm(3) Library Functions Manual alarm(3) NAME
alarm, ualarm - Sets or changes the timeout of interval timers. LIBRARY
Standard C Library (libc) SYNOPSIS
#include <unistd.h> unsigned int alarm( unsigned int seconds); useconds_t ualarm( useconds_t useconds, useconds_t interval); STANDARDS
Interfaces documented on this reference page conform to industry standards as follows: alarm(), ualarm(): XSH5.0 Refer to the standards(5) reference page for more information about industry standards and associated tags. PARAMETERS
Specifies a number of real-time seconds. Specifies a number of real-time microseconds. Specifies the interval for repeating the timer. DESCRIPTION
The alarm() function is used to obtain notification of a timeout after the number of real-time seconds specified by the seconds parameter has elapsed. At some time after seconds seconds have elapsed, a signal is delivered to the process. Each call resets the timer to the new value. A value of 0 (zero) disables the timer. When the notification signal is caught or ignored, no action takes place; otherwise the calling process is terminated. The alarm() function uses the ITIMER_REAL interval timer. The ualarm() function is used to obtain notification of a timeout after the number of real-time microseconds specified by the useconds parameter has elapsed. When the interval parameter is nonzero, timeout notification occurs after the number of microseconds specified by the interval parameter has been added to the useconds parameter. When the notification signal is caught or ignored, no action takes place; otherwise the calling process is terminated. The ualarm() function is the simplified interface to the setitimer() function, and uses the ITIMER_REAL interval timer. NOTES
The alarm() and ualarm() functions are supported for multithreaded applications. Although the alarm() and ualarm() functions are reentrant, it should be noted that just as the second of two calls from a single thread to alarm() resets the timer, this is also true if two calls are made from different threads. RETURN VALUES
If there is a previous alarm() request with time remaining, the alarm() function returns a non-zero value that is the number of seconds until the previous request would have generated a SIGALRM signal. Otherwise, alarm() returns 0 (zero). The ualarm() function returns the number of microseconds remaining from the previous ualarm() call. If no timeouts are pending or if ualarm() has not previously been called, ualarm() returns 0 (zero). ERRORS
The alarm() function sets errno to the specified values for the following conditions: [Tru64 UNIX] The seconds parameter specifies a value greater than 100,000,000. RELATED INFORMATION
Functions: gettimer(3) Standards: standards(5) delim off alarm(3)