signal_action

To control the reaction of a current process to a particular signal or set of signals, use the action() function. The action function takes either a signal or a set of signals as its first argument and takes an os_signal_action object as its second argument.

An os_signal_action object specifies how a process reacts to signals. The default constructor creates a signal action that reacts to the signal in the default way. Another constructor creates a signal action that calls a used-supplied handler, which takes the following parameters.

An optional set of signals added to the set of blocked signals during the execution of the handler and removed after the handler is finished.
An optional set of bitwise OR flags. These flags are described below.

SA_RESETHAND -Resets handler to the default action after the signal is received once.
SA_INTERRUPT -Interrupts automatic reset if a reentrant system call is executing when the signal is received.
SA_NOCLDSTOP -Does not send a SIGCHLD to the current process when one of its children terminates.

A pointer to a user-supplied handler with prototype void (*handler) (int) . When the handler is called, the signal number is passed as its argument. If the handler is equal to SIG_DFL , the default action is performed. If the handler is equal to SIG_IGN , the signal is ignored. For clarity, use restore_default() and ignore() rather than the SIG_DFL and SIG_IGN options.

In the following example, the current process installs a special handler for SIGALRM and sets its alarm clock to generate a SIGALRM signal after two seconds. The process then executes a pause() , causing the process to sleep until a signal is received.

The first time the signal is received, the handler executes and displays the received signal. Because the handler is not installed with the SA_RESETHAND option, the handler is restored to its default action.

The second time the signal is received, the default action is performed, displaying "Alarm Clock" and terminating without a core dump.

Example <ospace/unix/examples/signal7.cpp>


  #include <iostream>
#include <ospace/unix.h>

void
alarm_handler( int signal )
  {
  cout << os_signal( signal ) << " was received" << endl;
  }

int
main()
  {
  os_unix_toolkit initialize;

  os_this_process::action( SIGALRM, alarm_handler );

  cout << "Set my alarm for 2 seconds." << endl;
  os_this_process::set_repeat_alarm( 2 );

  cout << "Wait for a signal..." << endl;
  os_this_process::pause();

  cout << "Wait for a signal..." << endl;
  os_this_process::pause();
  return 0;
  }

Set my alarm for 2 seconds.
Wait for a signal...
os_signal( 14, Alarm Clock ) was received
Wait for a signal...
os_signal( 14, Alarm Clock ) was received