Signals (ITI8510) - Redigeerimiste ajalugu

Irve: /* Sending signals from keyboard */

2014-10-01T18:31:32Z

Sending signals from keyboard

←Vanem redaktsioon		Redaktsioon: 1. oktoober 2014, kell 20:31
12. rida:		12. rida:
	# Ctrl-\ sends a QUIT signal (SIGQUIT), which terminates the process (with [http://en.wikipedia.org/wiki/Core_dump coredump]).		# Ctrl-\ sends a QUIT signal (SIGQUIT), which terminates the process (with [http://en.wikipedia.org/wiki/Core_dump coredump]).
	# Ctrl-Z sends a TSTP signal (SIGTSTP), which makes the program to stop and suspend execution. To get it running again, use 'fg' (foreground) and 'bg' (background) utilities from command-line.		# Ctrl-Z sends a TSTP signal (SIGTSTP), which makes the program to stop and suspend execution. To get it running again, use 'fg' (foreground) and 'bg' (background) utilities from command-line.
	# Ctrl-S sends TSTP signal, but does not give you the command line. To start the program again, press Ctrl+Q. ''This often happens when one is used to GUI editors where Ctrl-S is Save command.''		# Ctrl-S sends TSTP signal, but does not give you the command line. To start the program again, press Ctrl+Q. ''This often happens when one is used to GUI editors where Ctrl-S is Save command. (And it seems that the command has been deprecated for newer Linux versions)''

	= Task =		= Task =

Irve: /* Task */

2013-10-02T13:31:28Z

Task

←Vanem redaktsioon		Redaktsioon: 2. oktoober 2013, kell 15:31
22. rida:		22. rida:
	# Fix the error by blocking the signals while printf() runs. Use [http://linux.die.net/man/2/sigprocmask sigprocmask()] function for masking (blocking) signals. You might find [http://linux.die.net/man/3/sigemptyset sigemptyset()] useful. Remember to restore the original signal blocking behaviour afterwards. You are "protecting the critical section" by masking signals. ''Show the result here, or save a copy for next step''		# Fix the error by blocking the signals while printf() runs. Use [http://linux.die.net/man/2/sigprocmask sigprocmask()] function for masking (blocking) signals. You might find [http://linux.die.net/man/3/sigemptyset sigemptyset()] useful. Remember to restore the original signal blocking behaviour afterwards. You are "protecting the critical section" by masking signals. ''Show the result here, or save a copy for next step''
	# For real-life programs it is not practical to block signals on every printf() call. Re-write the program so, that ''handler'' sets a global variable which holds 1 when signal has arrived, and 0 when it hasn't. Print the number on signal arrival, otherwise the dot. Remember to re-set the global variable. Note that there might still be a need to block signals when the signal arrives during the checking itself. Did you set the global variable as 'volatile'? ''Show the result''		# For real-life programs it is not practical to block signals on every printf() call. Re-write the program so, that ''handler'' sets a global variable which holds 1 when signal has arrived, and 0 when it hasn't. Print the number on signal arrival, otherwise the dot. Remember to re-set the global variable. Note that there might still be a need to block signals when the signal arrives during the checking itself. Did you set the global variable as 'volatile'? ''Show the result''

			== Notes ==

			The use of signal() is deprecated in favour of sigaction(), but for our educational purposes the signal() function is slightly better. In real life take the effort to use sigaction().

	Note that signals are even more compilcated, it is possible for another signal to arrive while you are handling a signal (and it will pre-empt your handler). This can be prevented by masking some (or all) signals for the duration of the handler.		Note that signals are even more compilcated, it is possible for another signal to arrive while you are handling a signal (and it will pre-empt your handler). This can be prevented by masking some (or all) signals for the duration of the handler.

Irve: /* Task */

2013-10-02T13:29:07Z

Task

←Vanem redaktsioon		Redaktsioon: 2. oktoober 2013, kell 15:29
19. rida:		19. rida:
	# Update the program to catch ^C and not to terminate with the signal. (Use CTRL+\ to quit (test whether it works; alternative would be to press ^Z, then kill with the process number that ^Z prints).		# Update the program to catch ^C and not to terminate with the signal. (Use CTRL+\ to quit (test whether it works; alternative would be to press ^Z, then kill with the process number that ^Z prints).
	# Update the program to count ^C keypresses and print the number every time the key is pressed. Add a newline to avoid line-buffering issues.		# Update the program to count ^C keypresses and print the number every time the key is pressed. Add a newline to avoid line-buffering issues.
	# ~~If you wrote~~ a naïve interpretation (which I hope), you might end up with a situation in which the printf() from main-loop runs while the handler accesses printf(). This is an error for printf to run while running (this is called ''[http://en.wikipedia.org/wiki/Reentrant_%28subroutine%29 re-entrancy]''). ~~Try~~ to ~~produce such~~ an error.		# In a naïve interpretation (which I hope), you might end up with a situation in which the printf() from main-loop runs while the handler accesses printf(). This is an error for printf to run while running (this is called ''[http://en.wikipedia.org/wiki/Reentrant_%28subroutine%29 re-entrancy]''). Sadly it's not feasible to manifest an error here.
	# Fix the error by blocking the signals while printf() runs. Use [http://linux.die.net/man/2/sigprocmask sigprocmask()] function for masking (blocking) signals. You might find [http://linux.die.net/man/3/sigemptyset sigemptyset()] useful. Remember to restore the original signal blocking behaviour afterwards. You are "protecting the critical section" by masking signals. ''Show the result here, or save a copy for next step''		# Fix the error by blocking the signals while printf() runs. Use [http://linux.die.net/man/2/sigprocmask sigprocmask()] function for masking (blocking) signals. You might find [http://linux.die.net/man/3/sigemptyset sigemptyset()] useful. Remember to restore the original signal blocking behaviour afterwards. You are "protecting the critical section" by masking signals. ''Show the result here, or save a copy for next step''
	# For real-life programs it is not practical to block signals on every printf() call. Re-write the program so, that ''handler'' sets a global variable which holds 1 when signal has arrived, and 0 when it hasn't. Print the number on signal arrival, otherwise the dot. Remember to re-set the global variable. Note that there might still be a need to block signals when the signal arrives during the checking itself. Did you set the global variable as 'volatile'? ''Show the result''		# For real-life programs it is not practical to block signals on every printf() call. Re-write the program so, that ''handler'' sets a global variable which holds 1 when signal has arrived, and 0 when it hasn't. Print the number on signal arrival, otherwise the dot. Remember to re-set the global variable. Note that there might still be a need to block signals when the signal arrives during the checking itself. Did you set the global variable as 'volatile'? ''Show the result''

	Note that signals are even more compilcated, it is possible for another signal to arrive while you are handling a signal (and it will pre-empt your handler). This can be ~~achieved~~ by masking some (or all) signals for the duration of the handler. It is customary to write handlers as short as possible for the exact same reason and check their ~~(asynchronous)~~ arrival on a convenient occasion.		Note that signals are even more compilcated, it is possible for another signal to arrive while you are handling a signal (and it will pre-empt your handler). This can be prevented by masking some (or all) signals for the duration of the handler.

			It is customary to write handlers as short as possible for the exact same reason and check their arrival on a convenient occasion in your program itself.

	[[Kategooria:RTOS]]		[[Kategooria:RTOS]]

Irve: /* Task */

2011-03-16T19:15:29Z

Task

←Vanem redaktsioon		Redaktsioon: 16. märts 2011, kell 21:15
16. rida:		16. rida:
	= Task =		= Task =

	# Write a small program with an infinite loop, which prints a dot (.) for every 1/2 seconds (use [http://linux.die.net/man/2/usleep usleep()] and printf() for educational fun), add a newline to escape [http://www.gnu.org/s/libc/manual/html_node/Buffering-Concepts.html line-buffering]. Check its reaction to CTRL+C		# Write a small program with an infinite loop, which prints a dot (.) for every 1/2 seconds (use [http://linux.die.net/man/3/usleep usleep()] and printf() for educational fun), add a newline to escape [http://www.gnu.org/s/libc/manual/html_node/Buffering-Concepts.html line-buffering]. Check its reaction to CTRL+C
	# Update the program to catch ^C and not to terminate with the signal. (Use CTRL+\ to quit (test whether it works; alternative would be to press ^Z, then kill with the process number that ^Z prints).		# Update the program to catch ^C and not to terminate with the signal. (Use CTRL+\ to quit (test whether it works; alternative would be to press ^Z, then kill with the process number that ^Z prints).
	# Update the program to count ^C keypresses and print the number every time the key is pressed. Add a newline to avoid line-buffering issues.		# Update the program to count ^C keypresses and print the number every time the key is pressed. Add a newline to avoid line-buffering issues.

Irve: /* Task */

2011-03-16T19:15:09Z

Task

←Vanem redaktsioon		Redaktsioon: 16. märts 2011, kell 21:15
16. rida:		16. rida:
	= Task =		= Task =

	# Write a small program with an infinite loop, which prints a dot (.) for every 1/2 seconds (use usleep() and printf() for educational fun), add a newline to escape [http://www.gnu.org/s/libc/manual/html_node/Buffering-Concepts.html line-buffering]. Check its reaction to CTRL+C		# Write a small program with an infinite loop, which prints a dot (.) for every 1/2 seconds (use [http://linux.die.net/man/2/usleep usleep()] and printf() for educational fun), add a newline to escape [http://www.gnu.org/s/libc/manual/html_node/Buffering-Concepts.html line-buffering]. Check its reaction to CTRL+C
	# Update the program to catch ^C and not to terminate with the signal. (Use CTRL+\ to quit (test whether it works; alternative would be to press ^Z, then kill with the process number that ^Z prints).		# Update the program to catch ^C and not to terminate with the signal. (Use CTRL+\ to quit (test whether it works; alternative would be to press ^Z, then kill with the process number that ^Z prints).
	# Update the program to count ^C keypresses and print the number every time the key is pressed. Add a newline to avoid line-buffering issues.		# Update the program to count ^C keypresses and print the number every time the key is pressed. Add a newline to avoid line-buffering issues.

Irve: /* Sending signals */

2011-03-16T19:03:12Z

Sending signals

←Vanem redaktsioon		Redaktsioon: 16. märts 2011, kell 21:03
4. rida:		4. rida:
	Signal handling on POSIX is done using either [http://linux.die.net/man/2/signal signal()] or [http://linux.die.net/man/2/sigaction sicaction()] functions. Both of those register a specific ''handler'' function for the arriving signal.		Signal handling on POSIX is done using either [http://linux.die.net/man/2/signal signal()] or [http://linux.die.net/man/2/sigaction sicaction()] functions. Both of those register a specific ''handler'' function for the arriving signal.

	= Sending signals =		= Sending signals from keyboard =

	You can send a signal to a process with [http://linux.die.net/man/2/kill kill()] system call. For sending a signal from command-line you can use the 'kill' utility with associated process number and signal number. While interesting, it is inconvenient for this practice.		You can send a signal to a process with [http://linux.die.net/man/2/kill kill()] system call. For sending a signal from command-line you can use the 'kill' utility with associated process number and signal number. While interesting, it is inconvenient for this practice.
12. rida:		12. rida:
	# Ctrl-\ sends a QUIT signal (SIGQUIT), which terminates the process (with [http://en.wikipedia.org/wiki/Core_dump coredump]).		# Ctrl-\ sends a QUIT signal (SIGQUIT), which terminates the process (with [http://en.wikipedia.org/wiki/Core_dump coredump]).
	# Ctrl-Z sends a TSTP signal (SIGTSTP), which makes the program to stop and suspend execution. To get it running again, use 'fg' (foreground) and 'bg' (background) utilities from command-line.		# Ctrl-Z sends a TSTP signal (SIGTSTP), which makes the program to stop and suspend execution. To get it running again, use 'fg' (foreground) and 'bg' (background) utilities from command-line.
			# Ctrl-S sends TSTP signal, but does not give you the command line. To start the program again, press Ctrl+Q. ''This often happens when one is used to GUI editors where Ctrl-S is Save command.''

	= Task =		= Task =

Irve: /* Task */

2011-03-16T18:59:21Z

Task

←Vanem redaktsioon		Redaktsioon: 16. märts 2011, kell 20:59
15. rida:		15. rida:
	= Task =		= Task =

	# Write a small program with an infinite loop, which prints a dot (.) for every 1/2 seconds (use usleep() ~~from last time~~ and printf() for educational fun), add a newline to escape [http://www.gnu.org/s/libc/manual/html_node/Buffering-Concepts.html line-buffering]. Check its reaction to CTRL+C		# Write a small program with an infinite loop, which prints a dot (.) for every 1/2 seconds (use usleep() and printf() for educational fun), add a newline to escape [http://www.gnu.org/s/libc/manual/html_node/Buffering-Concepts.html line-buffering]. Check its reaction to CTRL+C
	# Update the program to catch ^C and not to terminate with the signal. (Use CTRL+\ to quit (test whether it works; alternative would be to press ^Z, then kill with the process number that ^Z prints).		# Update the program to catch ^C and not to terminate with the signal. (Use CTRL+\ to quit (test whether it works; alternative would be to press ^Z, then kill with the process number that ^Z prints).
	# Update the program to count ^C keypresses and print the number every time the key is pressed. Add a newline to avoid line-buffering issues.		# Update the program to count ^C keypresses and print the number every time the key is pressed. Add a newline to avoid line-buffering issues.

Irve: /* Task */

2010-02-25T15:53:25Z

Task

←Vanem redaktsioon		Redaktsioon: 25. veebruar 2010, kell 17:53
15. rida:		15. rida:
	= Task =		= Task =

	# Write a small program with an infinite loop, which prints a dot (.) for every 1/2 seconds (use usleep() from last time and printf() for educational fun), add a newline to escape line-buffering. Check its reaction to CTRL+C		# Write a small program with an infinite loop, which prints a dot (.) for every 1/2 seconds (use usleep() from last time and printf() for educational fun), add a newline to escape [http://www.gnu.org/s/libc/manual/html_node/Buffering-Concepts.html line-buffering]. Check its reaction to CTRL+C
	# Update the program to catch ^C and not to terminate with the signal. (Use CTRL+\ to quit (test whether it works; alternative would be to press ^Z, then kill with the process number that ^Z prints).		# Update the program to catch ^C and not to terminate with the signal. (Use CTRL+\ to quit (test whether it works; alternative would be to press ^Z, then kill with the process number that ^Z prints).
	# Update the program to count ^C keypresses and print the number every time the key is pressed. Add a newline to avoid line-buffering issues.		# Update the program to count ^C keypresses and print the number every time the key is pressed. Add a newline to avoid line-buffering issues.

Irve: /* Task */

2010-02-25T15:52:45Z

Task

←Vanem redaktsioon		Redaktsioon: 25. veebruar 2010, kell 17:52
15. rida:		15. rida:
	= Task =		= Task =

	# Write a small program with an infinite loop, which prints a dot (.)for every 1/2 seconds (use usleep() from last time and printf() for educational fun). Check its reaction to CTRL+C		# Write a small program with an infinite loop, which prints a dot (.) for every 1/2 seconds (use usleep() from last time and printf() for educational fun), add a newline to escape line-buffering. Check its reaction to CTRL+C
	# Update the program to catch ^C and not to terminate with the signal. (Use CTRL+\ to quit (test whether it works; alternative would be to press ^Z, then kill with the process number that ^Z prints).		# Update the program to catch ^C and not to terminate with the signal. (Use CTRL+\ to quit (test whether it works; alternative would be to press ^Z, then kill with the process number that ^Z prints).
	# Update the program to count ^C keypresses and print the number every time the key is pressed. Add a newline to avoid line-buffering issues.		# Update the program to count ^C keypresses and print the number every time the key is pressed. Add a newline to avoid line-buffering issues.

Irve: /* Task */

2010-02-25T15:14:31Z

Task

←Vanem redaktsioon		Redaktsioon: 25. veebruar 2010, kell 17:14
15. rida:		15. rida:
	= Task =		= Task =

	# Write a small program with an infinite loop, which prints a dot (.)for every ~~500 milliseconds~~ (use usleep() from last time and printf() for educational fun). Check its reaction to CTRL+C		# Write a small program with an infinite loop, which prints a dot (.)for every 1/2 seconds (use usleep() from last time and printf() for educational fun). Check its reaction to CTRL+C
	# Update the program to catch ^C and not to terminate with the signal. (Use CTRL+\ to quit (test whether it works; alternative would be to press ^Z, then kill with the process number that ^Z prints).		# Update the program to catch ^C and not to terminate with the signal. (Use CTRL+\ to quit (test whether it works; alternative would be to press ^Z, then kill with the process number that ^Z prints).
	# Update the program to count ^C keypresses and print the number every time the key is pressed. Add a newline to avoid line-buffering issues.		# Update the program to count ^C keypresses and print the number every time the key is pressed. Add a newline to avoid line-buffering issues.