dksignal(3) - Linux man page

Name

dksignal - portable signal handling

Synopsis

#include <dksignal.h>

dk_signal_ret_t my_handler(int signo)
{
  dksignal_refresh(signo, handler);
  /* ... real signal processing ... */
}

typedef dk_signal_ret_t dk_signal_fct_t(int signo);

typedef dk_signal_fct_t *dk_signal_disp_t;

int dksignal_available(void);

dk_signal_disp_t dksignal_set(int signo, dk_signal_disp_t newfct);

Description

On Unix there are different signal handling mechanisms available:

• signal()
Primitive signal handling. This mechanism has two drawback:: + Arrival of a new signal while a signal handler is running interrupts the signal handler.; + Before the signal handler is activated, the signal disposition is set to the default. The signal handler must re-activate itself in order to receive the same signal again. Even if the signal handler re-activates itself as first instruction there is a little timing window in which signals are not caught properly.
• sigset()
The sigset() mechanism installs permanent signal handlers, so there is no such race condition as shown for the signal() mechanism. If another signal arrives while a signal handler is running, the running signal handler is finished before running the signal handler for the next signal.
• POSIX signal handling
A yet more powerfull mechanism to handle signals.
Portable source code must be able to use all three mechanisms, programs should issue a warning if the signal() mechanism is used. If possible the dksignal module uses sigset() or POSIX sigaction(), if none of this is available signal() is used. The my_handler() function is an example for a signal handler function. The dksignal_refres() macro re-activates the signal handler if the signal() mechanism is in use. If sigset() or sigaction() is used the macro does nothing. The dk_signal_ret_t is the return type of signal handlers, this is either void or int. The dk_signal_fct_t is the function type for signal handlers. The dk_signal_disp_t is a type to store pointers to signal handler functions. The dksignal_set() function establishes a new signal handler for the given signal number. A pointer to the old signal disposition is returned. This can be used to re-establish the old signal disposition before exiting the program. The dksignal_available() function shows which signal processing mechanism is in use. It returns 0 for signal() (the program should issue a warning in this case), 1 for sigset() and 2 for sigaction().

Author

Dirk Krause

Copyright And License

Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met:

* Redistributions of source code must retain the above
  copyright notice, this list of conditions and the
  following disclaimer.

* Redistributions in binary form must reproduce the above
  copyright notice, this list of conditions and the following
  disclaimer in the documentation and/or other materials
  provided with the distribution.

* Neither the name of the Dirk Krause nor the names of
  contributors may be used to endorse or promote products
  derived from this software without specific prior written
  permission.

THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS " AS IS " AND ANY EXPRESS OR IMPLIED WARRANTIES , INCLUDING , BUT NOT LIMITED TO , THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED . IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT , INDIRECT , INCIDENTAL , SPECIAL , EXEMPLARY , OR CONSEQUENTIAL DAMAGES ( INCLUDING , BUT NOT LIMITED TO , PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES ; LOSS OF USE , DATA , OR PROFITS ; OR BUSINESS INTERRUPTION ) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY , WHETHER IN CONTRACT , STRICT LIABILITY , OR TORT ( INCLUDING NEGLIGENCE OR OTHERWISE ) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE , EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE .

Referenced By

dkport(3)