Inter-process communication code examples and related functions interpretations
Exercise: The user designs two programs, requiring the corresponding excuse of custom signal SIGUSR1 in process A, and requiring process B to send a SIGUSR1 signal to process A every once in a while, testing whether process A can execute the associated corresponding interface.
1. Set up signal processing handler in processA
#include <>
#include <>
// Signal processing function
void handler(int sig)
{
switch (sig)
{
case SIGUSR1:
printf("user1 signal received\n");
break;
default:
break;
}
}
int main(int argc, char const *argv[])
{
signal(SIGUSR1, handler); // Set signal processing function
while (1);
return 0;
}There are two sign entries in Chapter 7 of Linux Manual. Users can customize signal behavior.SIGUSR1andSIGUSR2, customize it hereSIGUSR1：
Signal Standard Action Comment ──────────────────────────────────────────────────────────────────────── SIGABRT P1990 Core Abort signal from abort(3) SIGALRM P1990 Term Timer signal from alarm(2) SIGBUS P2001 Core Bus error (bad memory access) SIGCHLD P1990 Ign Child stopped or terminated SIGCLD - Ign A synonym for SIGCHLD SIGCONT P1990 Cont Continue if stopped SIGEMT - Term Emulator trap SIGFPE P1990 Core Floating-point exception SIGHUP P1990 Term Hangup detected on controlling terminal or death of controlling process SIGILL P1990 Core Illegal Instruction SIGINFO - A synonym for SIGPWR SIGINT P1990 Term Interrupt from keyboard SIGIO - Term I/O now possible (4.2BSD) SIGIOT - Core IOT trap. A synonym for SIGABRT SIGKILL P1990 Term Kill signal SIGLOST - Term File lock lost (unused) SIGPIPE P1990 Term Broken pipe: write to pipe with no readers; see pipe(7) SIGPOLL P2001 Term Pollable event (Sys V); synonym for SIGIO SIGPROF P2001 Term Profiling timer expired SIGPWR - Term Power failure (System V) SIGQUIT P1990 Core Quit from keyboard SIGSEGV P1990 Core Invalid memory reference SIGSTKFLT - Term Stack fault on coprocessor (unused) SIGSTOP P1990 Stop Stop process SIGTSTP P1990 Stop Stop typed at terminal SIGSYS P2001 Core Bad system call (SVr4); see also seccomp(2) SIGTERM P1990 Term Termination signal SIGTRAP P2001 Core Trace/breakpoint trap SIGTTIN P1990 Stop Terminal input for background process SIGTTOU P1990 Stop Terminal output for background process SIGUNUSED - Core Synonymous with SIGSYS SIGURG P2001 Ign Urgent condition on socket (4.2BSD) SIGUSR1 P1990 Term User-defined signal 1 SIGUSR2 P1990 Term User-defined signal 2 SIGVTALRM P2001 Term Virtual alarm clock (4.2BSD) SIGXCPU P2001 Core CPU time limit exceeded (4.2BSD); see setrlimit(2) SIGXFSZ P2001 Core File size limit exceeded (4.2BSD); see setrlimit(2) SIGWINCH - Ign Window resize signal (4.3BSD, Sun)
Chapter 2 of linux explains the use of signal functions:
SIGNAL(2) Linux Programmer's Manual SIGNAL(2)
NAME
signal - ANSI C signal handlingSYNOPSIS
#include <> typedef void (*sighandler_t)(int); sighandler_t signal(int signum, sighandler_t handler);DESCRIPTION
signal() sets the disposition of the signal signum to handler, which is either SIG_IGN, SIG_DFL, or the address of a programmer-defined function (a "signal handler").
signalshandler _t specifies the type of incoming signal processing function, internally as signal parameters, and the return value is void. When the program receivesSIGUSR1The handler will be triggered when the signal is signaled.
2. Send signals in processB
#include <sys/>
#include <>
#include <>
int main(int argc, char const *argv[])
{
While (1)
{
kill(4778, SIGUSR1); // Query the process pid of process A in advance
sleep(1);
}
return 0;
}man 2 kill：
KILL(2) Linux Programmer's Manual KILL(2)
NAME
kill - send signal to a processSYNOPSIS
#include <sys/>
#include <> int kill(pid_t pid, int sig);
Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
kill(): _POSIX_C_SOURCE
DESCRIPTION
The kill() system call can be used to send any signal to any process group or process.
Testing procedures
dada@dada-virtual-machine:~/test$ ./processA
Received user1 signal
Received user1 signal
Received user1 signal
Received user1 signal
Received user1 signal
Received user1 signal...
Test successfully