I run my game on linux system of TV, when I exit game, the system will crash.
from the output log, I know my game has been quite, but system crash following.
the main function like below:
int main(int argc, char** argv)
{
......
SDL_Quit();
printf("Log: exit end. \n);// it's printed on console
return 0;
}
I can find the output log about Log: exit end. So the game has been exit right?
I found the game exit will only crash after create threads.
Here is the run function in thread below:
while ( pThread->m_running )
{
string str;
string cmdStr;
if ( pThread->GetSendMsg(str, cmdStr) )
{
string returnStr = Connection::DealHttpSendMsg( str, cmdStr );
pThread->AddReturnMsg( returnStr );
haveData = true;
}
else
{
SDL_Delay(100);
haveData = false;
}
}
My question is that if the m_running is alway true. so when I exit the game, the thread is still running. Will it cause the crash?
It will if that thread tries to access resources that are being simultaneously destroyed by the main thread.
Just quitting the app won't crash it if you have a worker thread that does nothing.
#include <stdio.h>
#include <unistd.h>
#include <pthread.h>
void* run_me(void*)
{
while (1)
{
printf("Sleeping..\n");
sleep(1);
}
}
int main()
{
pthread_t my_thread;
pthread_create(&my_thread, NULL, &run_me, NULL);
sleep(2);
return 0;
}
return 0; terminates only the main thread. Try to use exit(0) instead.
Related
Problem
I wish to be able to pause the execution of a thread from a different thread. Note the thread paused should not have to cooperate. The pausing of the target thread does not have to occur as soon as the pauser thread wants to pause. Delaying the pausing is allowed.
I cannot seem to find any information on this, as all searches yielded me results that use condition variables...
Ideas
use the scheduler and kernel syscalls to stop the thread from being scheduled again
use debugger syscalls to stop the target thread
OS-agnostic is preferable, but not a requirement. This likely will be very OS-dependent, as messing with scheduling and threads is a pretty low-level operation.
On a Unix-like OS, there's pthread_kill() which delivers a signal to a specified thread. You can arrange for that signal to have a handler which waits until told in some manner to resume.
Here's a simple example, where the "pause" just sleeps for a fixed time before resuming. Try on godbolt.
#include <unistd.h>
#include <pthread.h>
#include <signal.h>
#include <string.h>
#include <errno.h>
#include <stdlib.h>
void safe_print(const char *s) {
int saved_errno = errno;
if (write(1, s, strlen(s)) < 0) {
exit(1);
}
errno = saved_errno;
}
void sleep_msec(int msec) {
struct timespec t = {
.tv_sec = msec / 1000,
.tv_nsec = (msec % 1000) * 1000 * 1000
};
nanosleep(&t, NULL);
}
void *work(void *unused) {
(void) unused;
for (;;) {
safe_print("I am running!\n");
sleep_msec(100);
}
return NULL;
}
void handler(int sig) {
(void) sig;
safe_print("I am stopped.\n");
sleep_msec(500);
}
int main(void) {
pthread_t thr;
pthread_create(&thr, NULL, work, NULL);
sigset_t empty;
sigemptyset(&empty);
struct sigaction sa = {
.sa_handler = handler,
.sa_flags = 0,
};
sigemptyset(&sa.sa_mask);
sigaction(SIGUSR1, &sa, NULL);
for (int i = 0; i < 5; i++) {
sleep_msec(1000);
pthread_kill(thr, SIGUSR1);
}
pthread_cancel(thr);
pthread_join(thr, NULL);
return 0;
}
I'm not new to programming, but pretty new to Linux. I'm trying to use signals to asynchronously catch a push on a button, like this:
Run a worker thread which raises SIGUSR1 when the button is pushed.
Run a loop (main thread) around sigtimedwait() that will rotate info every two seconds (as long as the button is not pushed) or break (when the button is pushed).
According to the notes on sigtimedwait(), one should block the signals you want to wait for, then call sigtimedwait(). But I never see sigtimedwait() catching the blocked signals. I have run the code below in a few ways to see what happens with different scenarios:
Call to pthread_sigmask() disabled, call to signal() disabled,
result: programs exits with message "User defined signal 1".
Call to pthread_sigmask() disabled, call to signal() enabled, result:
message "Button 1 pressed sync1 hit" appears, sigtimedwait() always
returns EAGAIN.
Call to pthread_sigmask() enabled, call to signal() disabled, result:
message "Button 1 pressed" appears, sigtimedwait() always returns
EAGAIN.
Call to pthread_sigmask() enabled, call to signal() enabled, result
of course same as previous because the handler will not be called.
All as expected, except for the fact that sigtimedwait() doesn't seem to catch the signal when it's pending.
I've looked into similar code, e.g. this. But I don't understand how that particular code could work: SIGUSR1 isn't blocked, so raising that should immediately terminate the program (the default action for SIGUSR1).
It looks like I'm missing something here. What am I doing wrong? Or is the whole idea of using raise() in a worker thread wrong? I'm running this on a Raspberry Pi 3 with Raspbian Stretch (Debian 9.1), could there be a problem in that?
[I know printf() shouldn't be used in a signal handler, but for this purpose it works]
Any help appreciated, thx!
#include <stdio.h>
#include <stdlib.h>
#include <bcm2835.h>
#include <signal.h>
#include <pthread.h>
#include <errno.h>
#define PIN_BUTTON1 RPI_V2_GPIO_P1_22 // GPIO #24
// Thread function
void* check_button1(void* param)
{
while (true)
{
if (bcm2835_gpio_lev(PIN_BUTTON1) == HIGH)
{
printf("Button 1 pressed ");
raise(SIGUSR1);
}
delay(250);
}
}
// Signal handler, if applied
volatile sig_atomic_t usr_interrupt = 0;
void sync1(int sig)
{
printf("sync1 hit ... ");
usr_interrupt = 1;
}
int main(int argc, char** argv)
{
if (!bcm2835_init())
{
printf("Failed to initialize BCM2835 GPIO library.");
return 1;
}
bcm2835_gpio_fsel(PIN_BUTTON1, BCM2835_GPIO_FSEL_INPT);
sigset_t sigusr;
sigemptyset(&sigusr);
sigaddset(&sigusr, SIGUSR1);
pthread_sigmask(SIG_BLOCK, &sigusr, NULL);
signal(SIGUSR1, sync1);
// Start the threads to read the button pin state
pthread_t th1;
pthread_create(&th1, NULL, check_button1, NULL);
// Create a two second loop
struct timespec timeout = { 0 };
timeout.tv_sec = 2;
usr_interrupt = 0;
int nLoopCount = 0;
while (true)
{
printf("Loop %d, waiting %d seconds ... ", ++nLoopCount, timeout.tv_sec);
int nResult = sigtimedwait(&sigusr, NULL, &timeout);
if (nResult < 0)
{
switch (errno)
{
case EAGAIN: printf("EAGAIN "); break; // Time out, no signal raised, next loop
case EINTR: printf("EINTR "); break; // Interrupted by a signal other than SIGCHLD.
case EINVAL: printf("EINVAL "); exit(1); // Invalid timeout
default: printf("Result=%d Error=%d ", nResult, errno); break;
}
printf("\n");
continue;
}
printf("Signal %d caught\n", nResult);
}
return 0;
}
ADDENDUM: In the meantime, I got this working by replacing raise(SIGUSR1) by kill(getpid(), SIGUSR1). Strange, because according to the manual raise(x) is equivalent to kill(getpid, x) in single-threaded programs and to pthread_kill(pthread_self(), x) in multi-threaded ones. Replacing raise(SIGUSR1) by pthread_kill(pthread_self, SIGUSR1) has no effect. If anyone could explain this to me ...
My code is as follows,The first time ,alarm works very well and handler2() function can work. however, the alarm doesn't work after it implement "doMain()" in the "handler2()".
I mean after the second time print ""In main Pleasae input: \n"", handler2() doesn't wrok anymore.
I don't know why? My code as follows:
#include <stdlib.h>
#include <stdio.h>
#include <unistd.h>
#include <signal.h>
#include <setjmp.h>
#define MAX_LEN_COMM 64
jmp_buf jumper;
int stop =0; //o is not stop ,otherwise is stop;
void hanlder2();
void doMain();
void handler2()
{
int len_command = 0;
char character;
char commandStr[60];
printf("******************************\n");
printf("In Alarm Pleasae input: \n");
while((character=getchar())!='\n')
{
commandStr[len_command]=character;
len_command++;
}
commandStr[len_command]='\0';
printf("In Alarm input is %s\n",commandStr);
if (strcmp(commandStr,"N")==0||strcmp(commandStr,"n")==0){
printf("In Alarm You put no, we will stop alarm \n");
stop=1;
longjmp(jumper, 2);
}
else if(strcmp(commandStr,"Y")==0||strcmp(commandStr,"y")==0){
printf("In Alarm You put yes, we will continue alarm \n");
signal(SIGALRM, handler2);
alarm(5);
doMain();
}
}
void doMain(){
while(1){
setjmp(jumper);
if(stop==0){
signal(SIGALRM, handler2);
printf("return time %d\n",alarm(5));
}
int len_command = 0;
char character;
char commandStr[60];
printf("In main Pleasae input: \n");
while((character=getchar())!='\n')
{
commandStr[len_command]=character;
len_command++;
}
commandStr[len_command]='\0';
printf("In main input is %s\n",commandStr);
if (strcmp(commandStr,"N")==0||strcmp(commandStr,"n")==0){
printf("In main You put no\n");
}
else if(strcmp(commandStr,"Y")==0||strcmp(commandStr,"y")==0){
printf("In main You put yes\n");
}
}
}
void main()
{
doMain();
}
What you are doing is very wrong.
First, the signature of the handler should be void handler(int sig).
Second, there are very few functions that are safe to use within a handler so you should try to get out of a handler as quickly as possible and definitely not doing console i/o. You are using several unsafe library functions.
Lastly a signal handler is a function. It runs and returns to where your program was interrupted by the signal. During the time a handler runs signals of the same type are not deliverd. By calling doMain() from the handler - which is crazy - the handler never ends. Because it doesn't end you won't see any more alarm signals.
i got an assignment to write a simple linux shell ,
this is the code so far :
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <sys/wait.h>
#include <sys/types.h>
int main(int argc,char argv[])
{
char *token;
char command[50];
char tmp[256];
char *arg_command[]={"",0};
int pid,status,flag=0;
char *path = (char*)getenv("PATH");
while(1) // run always
{
printf("\n");
printf(getenv("PWD")); //print current dir
printf(": ");
gets(command);
if (strcmp(command,"exit")==0) //check for exit command
{
printf("bye\n");
break;
}
strcpy(tmp,path);
token = strtok(path,":");
while(token!=NULL)
{
arg_command[0] = command;
pid = fork();
if(pid>=0)
{
printf("\npid is:%d\n",pid);
if (pid==0) // child process is invoked
{
strcat(token,"/");
execv(strcat(token,command),arg_command);
exit(0);
}
else //parent process
{
wait(&status);
if(status==0)
}
}
else
{
printf("fork faild");
}
token = strtok(NULL,":");
}
if (flag == 1)
{
printf("no files or folders match this command\n");
}
strcpy(path,tmp);
}
return 0;
}
my question is how do i know whether execv was able to execute the command or not
because i want to output an error when ever the user entered a wrong command.
i also have a flag but because i cant check execv i cant use it .
Like most Unix/POSIX functions, exec* return an error code (-1) if they fail. errno will then tell you why it failed.
In fact, if they ever return, then something went wrong. Otherwise, the current process is replaced which means no code after is ever execute (exit(0) in your case).
I am working in the Linux environment, and I have a C++ program, what I want is when I cancel the program with ctrl+c I would like that the program executes a function, to close some files and print some sutff, is there any way to do this?. Thank you.
signal() can be dangerous on some OSes and is deprecated on Linux in favor of sigaction(). "signal versus sigaction"
Here's an example that I ran across recently ("Tap the interrupt signal") and modified as I was playing around with it.
#include<stdio.h>
#include<unistd.h>
#include<signal.h>
#include<string.h>
struct sigaction old_action;
void sigint_handler(int sig_no)
{
printf("CTRL-C pressed\n");
sigaction(SIGINT, &old_action, NULL);
kill(0, SIGINT);
}
int main()
{
struct sigaction action;
memset(&action, 0, sizeof(action));
action.sa_handler = &sigint_handler;
sigaction(SIGINT, &action, &old_action);
pause();
return 0;
}
For a full working example you can try the following code:
#include <signal.h>
#include <stdio.h>
#include <stdbool.h>
volatile bool STOP = false;
void sigint_handler(int sig);
int main() {
signal(SIGINT, sigint_handler);
while(true) {
if (STOP) {
break;
}
}
return 0;
}
void sigint_handler(int sig) {
printf("\nCTRL-C detected\n");
STOP = true;
}
Example run:
[user#host]$ ./a.out
^C
CTRL-C detected
You have to catch the SIGINT. Something like this:
void sigint_handler(int sig)
{
[do some cleanup]
signal(SIGINT, SIG_DFL);
kill(getpid(), SIGINT);
}
loads more detail here
Short answer: look into the signal function, specifically catching SIGINT. You write a callback function and pass it to the system via the signal function, then when that particular signal happens, the system calls your callback function. You can close files and do whatever other cleanup stuff you want in there.
Note to people who might stumble upon this question, looking for the answer in Windows instead:
Use the SetConsoleCtrlHandler API call to set a custom handler and watch for CTRL_C_EVENT, CTRL_BREAK_EVENT or CTRL_CLOSE_EVENT.