Signal Handling--ref

/ Establish the signal handler. /
sigfillset (&block_mask);
usr_action.sa_handler = synch_signal;
usr_action.sa_mask = block_mask;
usr_action.sa_flags = 0;
sigaction (SIGUSR1,&usr_action,NULL);

/ Create the child process. /
child_id = fork ();
if (child_id == 0)
child_function (); / Does not return. /

/ Busy wait for the child to send a signal. /
while (!usr_interrupt)
;

/ Now continue execution. /
puts ("That's all,folks!");

return 0;
}

SIG_IGN. But it is useful to block signals briefly,to prevent them from interrupting sensitive operations. For instance:

You can use thesigprocmaskfunction to block signals while you modify global variables that are also modified by the handlers for these signals.
• You can setsa_maskin yoursigactioncall to block certain signals while a particular signal handler runs. This way,the signal handler can run without being interrupted itself by signals.

sigprocmaskgives you a way to prevent interrupts during critical parts of your code. If signals arrive in that part of the program,they are delivered later,after you unblock them.

sig_atomic_t(see section),then the signal handler could run when the rest of the program has only half finished reading or writing the data. This would lead to confusing consequences.

sig_atomic_t; you would like to test the flag and perform the action if the flag is not set. This is unreliable. Suppose the signal is delivered immediately after you test the flag,but before the consequent action: then the program will perform the action even though the signal has arrived.

`signal.h'.

sigset_t

Thesigset_tdata type is used to represent a signal set. Internally,it may be implemented as either an integer or structure type.

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