I'm trying to subscribe to a new signal handler in my current signal handler but nothing happens. No output from usr1b is printed in terminal, output from usr1a is printed in terminal.
Code:
#include<signal.h>
#include<stdio.h>
#include<unistd.h>
static int counter = 0;
void usr1b(int sig1) {
printf("usr1b\n");
counter++;
printf("current count: %d", counter);
}
void usr1a(int sig) {
printf("usr1a\n");
if( signal(SIGUSR1, usr1b) == SIG_ERR) {
printf("ERROR\n"); // subscribe usr1b to SIGUSR1
}
}
int main(void) {
if(signal(SIGINT, SIG_IGN)==SIG_ERR)
printf("ERROR"); // ignore SIGINT
if(signal(SIGUSR1, usr1a)==SIG_ERR)
printf("ERROR"); // subscribe usr1a to SIGUSR1
printf("Send some signal to process %d\n", getpid());
while (1) {
sleep(1);
}
return 0;
}
Try this...
static void usr1b(int signo) {
if (signo == SIGUSR1) {
cnt++;
printf("SIGUSR1 count: %d\n", cnt);
}
}
Related
In Linux, one can wait on any FD using select, poll or epoll.
It is also possible to wait for child-processes to change state using wait, waitpid or waitid.
However, I can't figure a way to combine these operations, i.e., to block the calling process until either some FD becomes ready or a child process changes state.
I can use polling, by repeatedly calling non-blocking epoll then waitid, but that is wasteful.
It is possible to create a pidfd for a child process (which is accepted by epoll), but pidfd only supports waiting for child termination, while I wish to wait for any state change (specifically, for ptrace stops).
Is this not possible in Linux?
You can wait for any child status change with signalfd() and make dummy read, then get actual status with waitpid():
sigset_t mask, old_set;
sigemptyset(&mask);
sigaddset(&mask, SIGCHLD);
sigprocmask(SIG_BLOCK, &mask, &old_set);
int sigfd = signalfd(-1, &mask, SFD_CLOEXEC);
if (sigfd == -1) {
perror("signalfd");
return 1;
}
for (int i = 0; i < 10; ++i) {
pid_t pid = fork();
if (pid == -1) {
perror("fork");
}
if (pid == 0) {
// Child process: restore blocked signals before exec() etc
sigprocmask(SIG_SETMASK, &old_set, NULL);
sleep(i % 3);
switch (i % 3) {
case 0:
raise(SIGSTOP);
break;
case 1:
raise(SIGABRT);
break;
}
exit(i);
}
printf("Spawned child %i with pid %u\n", i, pid);
}
for (;;) {
struct pollfd fds[] = {
{ .fd = STDIN_FILENO, .events = POLL_IN },
{ .fd = sigfd, .events = POLL_IN }
};
if (poll(fds, sizeof(fds)/sizeof(*fds), -1) == -1) {
perror("poll");
break;
}
if (fds[0].revents & POLL_IN) {
char buf[4096];
int ret = read(STDIN_FILENO, buf, sizeof(buf));
printf("Data from stdin: ");
fflush(stdout);
write(STDOUT_FILENO, buf, ret);
}
if (fds[1].revents & POLL_IN)
{
struct signalfd_siginfo fdsi;
read(sigfd, &fdsi, sizeof(fdsi));
for (;;) {
int status;
pid_t pid = waitpid(-1, &status, WNOHANG | WUNTRACED | WCONTINUED);
if (pid == -1) {
if (errno != ECHILD) {
perror("waitpid");
}
break;
}
if (pid == 0) {
break;
}
printf("Child %u ", pid);
if (WIFEXITED(status)) {
printf("exited with status %i\n", WEXITSTATUS(status));
} else if (WIFSIGNALED(status)) {
printf("terminated by signal %i\n", WTERMSIG(status));
} else if (WIFSTOPPED(status)) {
printf("stopped by signal %i\n", WSTOPSIG(status));
} else if (WIFCONTINUED(status)) {
printf("continued\n");
} else {
printf("status unknown\n");
}
}
}
}
close(sigfd);
Hello I'm trying IPC practice. But I have problem... Here is the code
Send_process.c (path : /home/John/h1/send_process.c)
struct mymsgbuf {
long mtype;
char mtext[80];
};
int main(void) {
key_t key;
int msgid;
struct mymsgbuf mesg;
char inputmsg[80];
if(msgid = msgget((key_t)123, IPC_CREAT | 0666) == -1) {
perror("Failed to create new MessageQueue");
exit(1);
}
printf("%d\n", msgid);
mesg.mtype = 1;
while(1) {
printf("Enter Sending Message. (Input exit, programm terminate) : ");
scanf("%s", inputmsg);
strcpy(mesg.mtext, inputmsg);
if(msgsnd(msgid, (void *)&mesg, sizeof(mesg.mtext), IPC_NOWAIT) == -1) {
perror("msgsnd");
exit(1);
}
if(strcmp(inputmsg, "exit") == 0) {
printf("Sending Process Terminated\n");
break;
}
}
return 0;
}
Receive_process.c (path : /home/John/h1/send_process.c)
struct mymsgbuf {
long mtype;
char mtext[80];
};
int main(void) {
struct mymsgbuf inmsg;
key_t key;
int msgid;
key = ftok("/home/John/h1/receive_process.c", 123);
if((msgid = msgget(key,0666)) < 0 ) { //here is error
perror("msgget");
exit(1);
}
printf("%d\n", msgid);
while(1) {
if(msgrcv(msgid, &inmsg, sizeof(inmsg.mtext), 0,0) == -1) {
perror("Message Receive");
exit(1);
}
printf("Received Message. Message is [%s]\n", inmsg.mtext);
if(strcmp(inmsg.mtext, "exit") == 0 ) {
printf("Receive_process end\n");
exit(0);
}
}
return 0;
}
Send_process is works very well, but Receive_process not works well. What is the problem?
My Driver Code :
static irqreturn_t pwm_cnt_interrupt(int irq, void *data)
{
printk("==> %s\r\n", __func__);
return IRQ_HANDLED;
}
static int ecap_cnt_probe(struct platform_device *pdev)
{
pc = devm_kzalloc(&pdev->dev, sizeof(*pc), GFP_KERNEL);
if (!pc)
return -ENOMEM;
clk = devm_clk_get(&pdev->dev, "fck");
if (IS_ERR(clk)) {
if (of_device_is_compatible(np, "ti,counter-ecap")) {
dev_warn(&pdev->dev, "Binding is obsolete.\n");
clk = devm_clk_get(pdev->dev.parent, "fck");
}
}
if (IS_ERR(clk)) {
dev_err(&pdev->dev, "failed to get clock\n");
return PTR_ERR(clk);
}
pc->clk_rate = clk_get_rate(clk);
if (!pc->clk_rate) {
dev_err(&pdev->dev, "failed to get clock rate\n");
return -EINVAL;
}
/* Get PWM IRQ number */
ecapirq = platform_get_irq(pdev, 0);
if (ecapirq < 0) {
printk(KERN_ERR "Could not get IRQ");
return -EINVAL;
}
printk(KERN_DEBUG "irq = %d\n", ecapirq);
oreore_dentry = debugfs_create_file("counter", 0666, NULL, &value, &fops);
if(request_irq(ecapirq, pwm_cnt_interrupt, IRQF_SHARED,
"counter", (void *)&counter)) {
printk(KERN_ERR "pwm counter: Can't allocate irq %d\n",
ecapirq);
return -EBUSY;
}
enable_irq(ecapirq);
return 0;
}
My Interrupt got registed in /proc/interrupts
But, Its not get triggered.
I have connected UART with my pwm interrupt pin. I m sending data using uart port. my irq handler is not get called at that time.
Need help on this.
I've written the program which spawns a thread that reads in a loop from stdin in a blocking fashion. I want to make the thread return from blocked read immediately. I've registered my signal handler (with sigaction and without SA_RESTART flag) in the reading thread, send it a signal and expect read to exit with EINTR error. But it doesn't happen. Is it issue or limitation of Cygwin or am I doing something wrong?
Here is the code:
#include <stdio.h>
#include <errno.h>
#include <pthread.h>
pthread_t thread;
volatile int run = 0;
void root_handler(int signum)
{
printf("%s ENTER (thread is %x)\n", __func__, pthread_self());
run = 0;
}
void* thr_func(void*arg)
{ int res;
char buffer[256];
printf("%s ENTER (thread is %x)\n", __func__, pthread_self());
struct sigaction act;
memset (&act, 0, sizeof(act));
act.sa_sigaction = &root_handler;
//act.sa_flags = SA_RESTART;
if (sigaction(SIGUSR1, &act, NULL) < 0) {
perror ("sigaction error");
return 1;
}
while(run)
{
res = read(0,buffer, sizeof(buffer));
if(res == -1)
{
if(errno == EINTR)
{
puts("read was interrupted by signal");
}
}
else
{
printf("got: %s", buffer);
}
}
printf("%s LEAVE (thread is %x)\n", __func__, pthread_self());
}
int main() {
run = 1;
printf("root thread: %x\n", pthread_self());
pthread_create(&thread, NULL, &thr_func, NULL);
printf("thread %x started\n", thread);
sleep(4);
pthread_kill(thread, SIGUSR1 );
//raise(SIGUSR1);
pthread_join(thread, NULL);
return 0;
}
I'm using Cygwin (1.7.32(0.274/5/3)).
I've just tried to do the same on Ubuntu and it works (I needed to include signal.h, though, even though in Cygwin it compiled as it is). It seems to be peculiarity of Cygwin's implementation.
This is my first Program....ctrlcsignal.c
enter code here
#include<stdio.h>
#include<unistd.h>
#include<signal.h>
void signal_handler(int sigNo)
{
//if Ctrl+c signal
if(sigNo==SIGINT){
printf("value of SIGINT:-%d\t",SIGINT);
printf("received SIGINT\n");
}
// if some other signal , but this part wont get executed
// as the signal_handler function is registered with SIGINT only
else
{
printf("Some other signal found");
printf("value of other signal:-%d",sigNo);
}
}
int main(void)
{
//registering the signal handler function with a signal
kill(19574,SIGUSR1);
if(signal(SIGINT,signal_handler)==SIG_ERR)
{
printf("\n can't catch SIGINT\n");
}
while(1) //infinite loop
sleep(1); // 1s ,so that the CPU is not busy
return 0;
}
and this my second program....userdefinedsignals.c
enter code here
#include <stdio.h>
#include <unistd.h>
#include <signal.h>
void signal_handler(int sigNo)
{
printf("function entered...");
// check for userdefined Signal SIGUSR1
if (sigNo == SIGUSR1)
{
printf("received SIGUSR1 with value :- %d",SIGUSR1);
}
//checking for KILL Signal
else if (sigNo == SIGKILL)
{
printf("received SIGKILL with value :- %d",SIGKILL);
}
//checking for STOP Signal
else if (sigNo == SIGSTOP)
{
printf("received SIGSTOP with value :- %d",SIGSTOP);
}
// if some other signal , but this part wont get executed
// as the signal_handler function is registered with SIGINT only
else
{
printf("Some other signal found");
printf("value of other signal:-%d",sigNo);
}
}
int main(void)
{
int pid_t;
printf("process id is %d",getpid());
//registering the signal handler function with a signal
if(signal(SIGUSR1,signal_handler) == SIG_ERR)
{
printf("\n can't catch SIGSIGUSR1\n");
}
if(signal(SIGKILL,signal_handler)==SIG_ERR)
{
printf("\n can't catch SIGKILL\n");
}
if(signal(SIGSTOP,signal_handler)==SIG_ERR)
{
printf("\n can't catch SIGSTOP\n");
}
while(1) //infinite loop
sleep(1); // 1s ,so that the CPU is not busy
return 0;
}
I get the pid of the second process ... suppose xxxx
then i use the following command...
enter code here
kill -USR1 xxxx
but it shows nothing ....
also then i tried by calling the following function int the first program...but no use..
enter code herekill(xxxx,SIGUSR1);
HELP ME..!!!!
Works here.
#include <stdio.h>
#include <unistd.h>
#include <signal.h>
#include <stdarg.h> /* vsnprintf() */
#include <signal.h> /* signal */
void myprintf(FILE *fp, char *fmt, ...)
{
char buff[512];
int rc,fd;
va_list argh;
va_start (argh, fmt);
rc = vsnprintf(buff, sizeof buff, fmt, argh);
if (rc < 0 || rc >= sizeof buff) {
rc = sprintf(buff, "Argh!: %d:\n", rc);
}
if (!fp) fp = stderr;
fd = fileno(fp);
if (fd < 0) return;
if (rc > 0) write(fd, buff, rc);
return;
}
void signal_handler(int sigNo)
{
switch (sigNo ) {
case SIGUSR1:
myprintf(NULL, "received SIGUSR1 with value :- %d\n", SIGUSR1);
break;
case SIGKILL:
myprintf(NULL, "received SIGKILL with value :- %d\n", SIGKILL);
break;
case SIGSTOP:
myprintf(NULL, "received SIGSTOP with value :- %d\n", SIGSTOP);
break;
default:
myprintf(NULL, "Some other signal occured: %d\n", sigNo);
break;
}
return;
}
int main(void)
{
pid_t mypid;
mypid = getpid();
printf("process id is %d\n", (int) mypid);
if(signal(SIGUSR1,signal_handler) == SIG_ERR)
{ printf("\n can't catch SIGSIGUSR1\n"); }
if(signal(SIGKILL,signal_handler)==SIG_ERR)
{ printf("\n can't catch SIGKILL\n"); }
if(signal(SIGSTOP,signal_handler)==SIG_ERR)
{ printf("\n can't catch SIGSTOP\n"); }
if(signal(SIGCONT,signal_handler)==SIG_ERR)
{ printf("\n can't catch SIGCONT\n"); }
while(1) {
sleep(1);
}
return 0;
}
You're catching the signal all right, but not seeing the message because you don't terminate lines properly, and the standard output stream on your system is line buffered (assuming your program runs in a terminal).
Standard C defines three levels of buffering for output streams:
unbuffered, where output is transmitted immediately
line buffered, where output is transmitted when a newline character is encountered
fully buffered, where output is transmitted when an internal buffer fills
(This is a simplification - see a C reference or the Standard for details).
Consider:
#include <stdio.h>
#include <unistd.h>
int main(void)
{
printf("Hello");
pause();
}
This produces no output in a terminal. Fix it by terminating the line:
printf("Hello\n");
This will produce the expected output in a terminal.
If stdout is not connected to a terminal - for example, you redirect to a file - then the stream becomes fully buffered. This:
./a.out > foo
Ctrl-C
cat foo
produces no output, even with the newline character added. Here you need an explicit flush to transmit the output before the buffer is full.
#include <stdio.h>
#include <unistd.h>
int main(void)
{
printf("Hello\n");
fflush(stdout);
pause();
}
This produces output even when redirected to a file.