Echo off problem in console application (Linux)

Question

Hello,

I am facing a strange problem in my console application.

First of all, the code snippet:

main.cpp

#include "DebugInterface.h"

static sigset_t signalSet;
static pthread_t CleanupHandlerThread;
DebugInterface* debugInterface = NULL;

void* CleanupHandler (void* param) {
    int32_t sig, err;
    err = sigwait (&signalSet, &sig);

    delete debugInterface;
    debugInterface = NULL;
    exit (EXIT_SUCCESS);

    return NULL;
}

int32_t main(int32_t argc, char** argv) {
    sigemptyset (&signalSet);
    sigaddset (&signalSet, SIGINT);
    pthread_sigmask (SIG_BLOCK, &signalSet, NULL);
    pthread_create (&CleanupHandlerThread, NULL, CleanupHandler, NULL);

    debugInterface = new DebugInterface();

    if (debugInterface != NULL) {
        debugInterface->StartReading();
    }

    while (true) {
        // Core functionality follows, but was commented out
        // (was not relevant for problem, checked it -
        // you may even remove this loop completely)
    }

    return EXIT_SUCCESS;
}

DebugInterface.h

#include <stdint.h>
#include <stdlib.h>
#include <stdio.h>
#include <iomanip>
#include <readline/readline.h>
#include <readline/history.h>
#include <signal.h>

class DebugInterface {
public:
    DebugInterface() { }
    virtual ~DebugInterface() { }

private:
    pthread_t ConsoleHandlerThread;

private:
    static void* ConsoleHandler (void* param);

public:
    bool StartReading();
};

DebugInterface.cpp

#include "DebugInterface.h"

void* DebugInterface::ConsoleHandler (void* param) {
    while (true) {
        char* input = readline ("\n> ");

        // Handle input, was commented out, too (irrelevant for problem)

        free (input);
    }

    return NULL;
}

bool DebugInterface::StartReading() {
    if (pthread_create (&ConsoleHandlerThread, NULL, DebugInterface::ConsoleHandler, NULL) != 0) {
        return false;
    }
    return true;
}

The code is running fine and as expected, but when it's exiting and terminating by catching the signal SIGINT, the console output afterwards is hidden (i.e. the console/terminal behaves like applying the command "stty -echo").

I've already inserted the code 'system ("stty echo");' in the function CleanupHandler before exiting and it "solved" the problem, but this can't be the right solution... Perhaps I am missing a severe fault that just doesn't show up. I also just don't figure out how my code affects the console output/terminal itself after terminating, because there isn't any system call/function call that may alter console behaviour (I am only using "printf" and color formatting for console output).

The code snippet above should reproduce the problem, compiler/linker configuration and output was:

make all 
Building file: ../main.cpp
Invoking: GCC C++ Compiler
g++ -O0 -g3 -Wall -c -fmessage-length=0 -MMD -MP -MF"main.d" -MT"main.d" -o"main.o" "../main.cpp"
Finished building: ../main.cpp

Building target: Testproject
Invoking: GCC C++ Linker
g++  -o"Testproject"  ./DebugInterface.o ./main.o   -lreadline -lpthread
Finished building target: Testproject

I am developing remotely on a server, problem occurs this way and over SSH, too, so this can't be any console bug. Additionally, putting console input handler in main thread and core functionality/loop in child thread doesn't make a difference.

Thanks in advance for any help.

Answer 1

Run the code under strace and you might spot exactly where the terminal output is being turned off.

Answer 2

Your program is not terminating cleanly when receiving a signal. The cause is the readline library.

Check what the readline documentation says about signal handling here

Answer 3

Thanks, adding two cleanup functions according to GNU Readline Library solved the problem.

You must add the following functions before expression "delete debugInterface;":

rl_cleanup_after_signal();
rl_free_line_state();

[...]

delete debugInterface;