Question

My goal is create text-based applications with JVM languages,
and now I am trying to use ncurses with JNI.

When I use ncurses directly from C, resizing the terminal will trigger getch() and return 410 (KEY_RESIZE).
But I use ncurses via JNI, getch() won t do anything until pressing any other keys.

Is it a limitation of JVM?
Any workaround for this situation?
or shouldn t I use ncurses via JNI in the first place?

Here is the full reproducible code:

public class Main {
    public static native void init();
    public static native int  getch();
    public static native void printw(String string);
    public static native void endwin();

    public static void main(String[] args) {
        System.loadLibrary("jcurses");
        init();
        for (int key; (key = getch()) !=  q ;)
            printw("%d
".formatted(key));
        endwin();
    }
}

#include <ncurses.h>
#include "Main.h"

JNIEXPORT void JNICALL Java_Main_init(JNIEnv *env, jclass clazz) {
    initscr();
    keypad(stdscr, TRUE);
    noecho();
}

JNIEXPORT jint JNICALL Java_Main_getch(JNIEnv *env, jclass clazz) {
    return (long) getch();
}

JNIEXPORT void JNICALL Java_Main_printw(JNIEnv *env, jclass clazz, jstring javaString) {
    const char *nativeString = (*env)->GetStringUTFChars(env, javaString, 0);
    printw("%s", nativeString);
    (*env)->ReleaseStringUTFChars(env, javaString, nativeString);
}

JNIEXPORT void JNICALL Java_Main_endwin(JNIEnv *env, jclass clazz) {
    endwin();
}

all:
    javac -h . Main.java
    gcc -I"$$JAVA_HOME/include" -I"$$JAVA_HOME/include/linux" jcurses.c -shared -o libjcurses.so -lncurses
run:
    java -Djava.library.path=. Main

For comparison, here is the pure C code to do the same thing.
Resizing the window will shows up 410 immediately but cannot do the same with JNI.

#include <ncurses.h>

int main() {
    initscr();
    keypad(stdscr, TRUE);
    noecho();
    for (int key; (key = getch()) !=  q ;)
        printw("%d
", key);
    endwin();
    return 0;
}

在以下装置上测试:

x86 ubuntu22.04, ssh from Windows 7 git bash
arm64 ubuntu22.04, native gnome terminal

Answer 1

I found that the issue is that the JVM "consumes" the SIGWINCH signal,
so that ncurses cannot detect the changes of the size of the window.

Therefore a possible solution is using the sun.misc.Signal class to catch the signal and do the rendering stuff,
but this is an absolutely bad idea due to its deprecation.

// WARNING! this package is deprecated!
import sun.misc.Signal;

Signal.handle(new Signal("WINCH"), signal -> {
    // re-render our contents
});

(这一答案不应接受)

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