C Signal Slot Library

Description:Signals are software interrupts delivered to a process by the operating system.Signals can also be issued by the operating system based on system or error conditions.There is a default behavior for some (i.e. a process is terminated when it receives an inturrupt SIGINT signal by pressing keystrokes ctrl-C) but this tutorial shows how to handle the signal by defining callback functions to manage the signal. Where possible, this allows one to close files and perform operations and react in a manner defined by the programmer.

The signal/slot library is ISO C compliant (at least where possible) and will work on pretty much anything. All you need is a reasonable C compiler that supports templates. You don't need partial template specialisation support, so VC6 and VC.NET are both fine. The Microsoft Foundation Classes (MFC) are a nightmarish mess. 1 Introduction This paper introduces the sigslot library, which implements a type-safe, thread-safe signal/slot mech- anism in C. The library is implemented entirely in C, and does not require source code to be pre- processed1in order for itto be used. The sigslot library’s home page is at http://sigslot.sourceforge.net/. The concept is that GUI widgets can send signals containing event information which can be received by other widgets / controls using special functions known as slots. This is similar to C/C function pointers, but signal/slot system ensures the type-correctness of callback arguments. 1 Introduction This paper introduces the sigslot library, which implements a type-safe, thread-safe signal/slot mech- anism in C. The library is implemented entirely in C, and does not require source code to be pre- processed1in order for itto be used. The sigslot library’s home page is at http://sigslot.sourceforge.net/. C signals and slots. Vdk-signals is a type-safe and thread-safe signals-slots system for standard C designed with performance and simplicity in mind. It follows the main philosophy of the C language avoiding unnecessary overheads and superfluous functionality that can slow down your program.

Note that not all signals can be handled.

Types of signals:

Signal	Value	Description
SIGHUP	1	Hangup (POSIX) Report that user's terminal is disconnected. Signal used to report the termination of the controlling process.
SIGINT	2	Interrupt (ANSI) Program interrupt. (ctrl-c)
SIGQUIT	3	Quit (POSIX) Terminate process and generate core dump.
SIGILL	4	Illegal Instruction (ANSI) Generally indicates that the executable file is corrupted or use of data where a pointer to a function was expected.
SIGTRAP	5	Trace trap (POSIX)
SIGABRT SIGIOT	6	Abort (ANSI) IOT trap (4.2 BSD) Process detects error and reports by calling abort
SIGBUS	7	BUS error (4.2 BSD) Indicates an access to an invalid address.
SIGFPE	8	Floating-Point arithmetic Exception (ANSI). This includes division by zero and overflow.The IEEE Standard for Binary Floating-Point Arithmetic (ANSI/IEEE Std 754-1985) defines various floating-point exceptions.
SIGKILL	9	Kill, unblockable (POSIX) Cause immediate program termination. Can not be handled, blocked or ignored.
SIGUSR1	10	User-defined signal 1
SIGSEGV	11	Segmentation Violation (ANSI) Occurs when a program tries to read or write outside the memory that is allocated for it by the operating system, dereferencing a bad or NULL pointer. Indicates an invalid access to valid memory.
SIGUSR2	12	User-defined signal 2
SIGPIPE	13	Broken pipe (POSIX) Error condition like trying to write to a socket which is not connected.
SIGALRM	14	Alarm clock (POSIX) Indicates expiration of a timer. Used by the alarm() function.
SIGTERM	15	Termination (ANSI) This signal can be blocked, handled, and ignored. Generated by 'kill' command.
SIGSTKFLT	16	Stack fault
SIGCHLD SIGCLD	17	Child status has changed (POSIX) Signal sent to parent process whenever one of its child processes terminates or stops. See the YoLinux.com Fork, exec, wait, waitpid tutorial
SIGCONT	18	Continue (POSIX) Signal sent to process to make it continue.
SIGSTOP	19	Stop, unblockable (POSIX) Stop a process. This signal cannot be handled, ignored, or blocked.
SIGTSTP	20	Keyboard stop (POSIX) Interactive stop signal. This signal can be handled and ignored. (ctrl-z)
SIGTTIN	21	Background read from tty (POSIX)
SIGTTOU	22	Background write to tty (POSIX)
SIGURG	23	Urgent condition on socket (4.2 BSD) Signal sent when 'urgent' or out-of-band data arrives on a socket.
SIGXCPU	24	CPU limit exceeded (4.2 BSD)
SIGXFSZ	25	File size limit exceeded (4.2 BSD)
SIGVTALRM	26	Virtual Time Alarm (4.2 BSD) Indicates expiration of a timer.
SIGPROF	27	Profiling alarm clock (4.2 BSD) Indicates expiration of a timer. Use for code profiling facilities.
SIGWINCH	28	Window size change (4.3 BSD, Sun)
SIGIO SIGPOLL	29	I/O now possible (4.2 BSD) Pollable event occurred (System V) Signal sent when file descriptor is ready to perform I/O (generated by sockets)
SIGPWR	30	Power failure restart (System V)
SIGSYS	31	Bad system call

See: /usr/include/bits/signum.h

Signals which can be processed include: SIGINT, SIGABRT, SIGFPE, SIGILL, SIGSEGV, SIGTERM, SIGHUP

List all signals available to the system:

Use the command: kill -l

Sending a process a signal:

A process can be sent a signal using the 'kill' command: kill -s signal-numberpid

Where the pid (process id) can be obtained using the 'ps' command.

Basic C signal callback function example:

File: signalExample.cpp

Example to handle ctrl-c
Compile: gcc signalExample.cpp
Run: a.out
Results:

The function prototype: void (*signal (int sig, void (*func)(int)))(int);

File: signalHandler.hpp

C++ Signal Slot

File: signalHandler.cppFile:

C Signal Slot Library Games

test.cpp

C Signal Slot Library App

Compile: g++ signalHandle.cpp test.cppC functions:

• signal - ANSI C signal handling
• raise - send a signal to the current process
• strsignal - return string describing signal (GNU extension)
• psignal - print signal message
• sigaction - POSIX signal handling functions
• sigsetops - POSIX signal set operations
• sigvec - BSD software signal facilities
• alarm - set an alarm clock for delivery of a signal

Commands:

• kill - terminate a process
• ps - report a snapshot of the current processes.

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