Why has no one written a threadsafe branch of the ncurses library?

问题

NCurses appears to be a popular library. One of its weaknesses is, that it is not threadsafe. It should not be hard to wrap shared ressources in mutexes.

Is there a specific reason, why noone has started a threadsafe branch? (Legal issues, introducing a platform dependency, ...)

Edit: I do not mean the use_screen or use_window functions. These apparently require the user to change his NCurses-based code. It should be possible to add a mutex to the shared resources within the NCurses itself, and all accessing functions acquire the mutex before doing something with the window. I am imagining something like this within NCurses:

#if __cplusplus >= 201103L
#include <mutex>
#define THREADSAFE
#endif
...
#ifdef THREADSAFE
std::recursive_mutex  mxCurscr;
#endif
...
int doupdate(void)
{
#ifdef THREADSAFE
mxCurscr.lock();
#endif
... // <-- Access the screen here.
#ifdef THREADSAFE
mxCurscr.unlock()
#endif
}

This does not rely on anything but the C++11 standard.
This is compatible with older compilers. (But no threadsafety then.)
It should not take more than one or two days to make the modifications.
This satisfies the demand for a threadsafe NCurses.
The user of the NCurses library will not have to bother.
The work is being done one time for all users, instead of having every user implementing its own thread-safety.

So, where is the catch?

回答1:

It's already been done (in ncurses 5.7, released November 2008), but not much used. See the curs_threads manual page for instance. It is not a feature in the default configuration because it

changes the ABI (application binary interface), and
adds some restrictions on how standard variables are used.

回答2:

Thread-safe code looks like this.

#include <stdio.h>
#include <ncurses.h>
#include <pthread.h>
#include <time.h>
#include <unistd.h>

pthread_mutex_t MUTEX;  /* mutex for sync display */

#define LOCK pthread_mutex_lock(&MUTEX)
#define UNLOCK pthread_mutex_unlock(&MUTEX)

typedef struct _WIN_struct {
    int startx, starty;
    int height, width;
} WIN;

WIN winTitle;      /* title win */
WIN winMenu;   /* Main menu win */
WIN winNews;       /* win news */

WINDOW *create_newwin(int height, int width, int starty, int startx) {
    WINDOW *local_win;
    local_win = newwin(height, width, starty, startx);
    box(local_win, 0, 0);
    wrefresh(local_win);
    return local_win;
}

char *getTimeNow() {
    time_t rawtime;
    struct tm *timeinfo;
    time(&rawtime);
    timeinfo = localtime(&rawtime);
    return asctime(timeinfo);
}

void *threadfunc_title(void *p) {
    WINDOW *windowTitle;
    LOCK;
    windowTitle = create_newwin(winTitle.height, winTitle.width, winTitle.starty, winTitle.startx);
    UNLOCK;

    /* show title and time */
    for (;;) {
        sleep(1);
    }

}

void *threadfunc_menu(void *p) {
    WINDOW *windowMenu;
    LOCK;
    windowMenu = create_newwin(winMenu.height, winMenu.width, winMenu.starty, winMenu.startx);
    UNLOCK;

    for (;;) {
        /* now do nothing */
        sleep(1);
    }

}

void *threadfunc_news(void *p) {
    WINDOW *windowNews;
    LOCK;
    windowNews = create_newwin(winNews.height, winNews.width, winNews.starty, winNews.startx);
    UNLOCK;

    for (;;) {
        sleep(1);
    }
}

void initWin(WIN *p_win, int height, int width, int starty, int startx) {
    p_win->height = height;
    p_win->width = width;
    p_win->starty = starty;
    p_win->startx = startx;
}


int main(int argc, char *argv[])
{
    pthread_t pidTitle;
    pthread_t pidMenu;
    pthread_t pidNews;

    initscr();
    start_color();
    cbreak();
    keypad(stdscr, TRUE);
    noecho();

    /* init location */
    initWin(&winTitle, LINES*0.25, COLS, 0 , 0);
    initWin(&winMenu, LINES*0.75, COLS*0.60, LINES*0.25, 0);
    initWin(&winNews, LINES*0.75, COLS*0.40, LINES*0.25, COLS*0.60);

    pthread_create(&pidTitle, NULL, threadfunc_title, NULL);
    pthread_create(&pidMenu, NULL, threadfunc_menu, NULL);
    pthread_create(&pidNews, NULL, threadfunc_news, NULL);

    pthread_join(pidTitle, NULL);
    pthread_join(pidMenu, NULL);
    pthread_join(pidNews, NULL);

    endwin();
    return 0;
}

来源：https://stackoverflow.com/questions/29910562/why-has-no-one-written-a-threadsafe-branch-of-the-ncurses-library

标签

thread-safety

ncurses