Working with the Unix OS

Processes I
func: argument specifies the address of a function
- SIG_DFL handle in default way
- SIG_IGN signal is to be ignored
sig: is the signal name
e.g.
signal (SIGUSR1, SIG_IGN);
- Call myintr function when SIGINT signal is generated:
#include
extern void myintr();
if (signal (SIGINT, SIG_IGN) != SIG_IGN)
signal (SIGINT, myintr);
! Reliable Signals
- Signals handlers remain installed after a signal occurs.
- A process must be able to prevent selected signals from occurring when desired.
- While a signal is being delivered to a process, that signal is blocked (held).
BSD4.3 supports the concept of a signal mask:
#include
int mask; /* 32 signals one per bit */
int oldmask;
mask = sigmask(SIGQUIT) | sigmask(SIGINT);
Want to block signals in critical region of code:
oldmask = sigblock( mask );
/* critical region */
sigsetmask(oldmask); /* reset to what is was */
System V use signal functions:
sighold(SIGQUIT);
sighold(SIGINT);
/* critical region */
sigrelse(SIGQUIT);
sigrelse(SIGINT);
BSD4.3 release one or more signals that are blocked:
int flag = 0; /* global set when SIGINT occurs */
for (; ;) {
sigblock(sigmask(SIGINT));
while (flag == 0)
sigpause(0); /* wait for signal */
/* signal has occurred, process it */
...
}
System V version:
int flag = 0; /* global set when SIGINT occurs */
for (; ;) {
sighold(SIGINT);
while (flag == 0)
sigpause(SIGINT); /* wait for signal */
/* signal has occurred, process it */
...}
! Process Control
Network programming involves the interaction of two or more processes. How are processes created, executed, and
terminated?
int fork(); /* system call */
Creates a copy of the process that was executing. The process that executed the fork is the parent and the new
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