我如何告诉 GTK 从外部更新应用程序？

Question

背景和问题

出于某些原因，我需要分叉我的代码并在两个分叉上更新一个变量。该变量通过mmap 存储在内存中，因此所有进程都可以访问它。在一个子进程中，我增加了变量。如何告诉 GTK 应用程序从子进程刷新/更新/重绘？

MWE

/*
 * Update GTK label from variable stored in mmap
 */

#include <stdlib.h>
#include <unistd.h>
#include <sys/mman.h>
#include <gtk/gtk.h>

static void activate (GtkApplication *app, gpointer localval) {
    GtkWidget *window;
    // Button Containers
    GtkWidget *button_box_quit;
    // Buttons
    GtkWidget *exit_button;
    // Text
    GtkWidget *text_status;
    
    // Define Window, dynamic size for screen.
    window = gtk_application_window_new (app);
    gtk_window_set_title (GTK_WINDOW (window), "test");
    gtk_window_set_default_size(GTK_WINDOW(window), 400, 300);
    
    // Define Button Boxes.
    button_box_quit = gtk_button_box_new(GTK_ORIENTATION_HORIZONTAL);
    
    // Define Exit Button, put it in a box, put box in window
    exit_button = gtk_button_new_with_label ("Exit");
    gtk_container_add(GTK_CONTAINER (button_box_quit), exit_button);
    gtk_container_add(GTK_CONTAINER (window), button_box_quit);

    // Connect signals to buttons
    g_signal_connect_swapped (exit_button, "clicked", G_CALLBACK (gtk_widget_destroy), window);
    
    // Define text status
    char msg[32]={0};
    // The "print" line
    g_snprintf(msg, sizeof msg, "val: %d\n", *(int *)localval);
    text_status = gtk_label_new(msg);
    gtk_container_add(GTK_CONTAINER (button_box_quit), text_status);
    
    //Activate!
    g_snprintf(msg, sizeof msg, "val: %d\n", *(int *)localval);
    gtk_label_set_text(GTK_LABEL(text_status), msg);
    gtk_widget_show_all (window);
}

int main (int argc, char **argv) {
    GtkApplication *app;
    int status;
    
    int *VAL = mmap(NULL, sizeof(int), PROT_READ|PROT_WRITE, MAP_SHARED|MAP_ANONYMOUS, -1, 0);
    int *ABORT = mmap(NULL, sizeof(int), PROT_READ|PROT_WRITE, MAP_SHARED|MAP_ANONYMOUS, -1, 0);
    int pid = fork();
    
    if (pid == 0) {
        while(!*ABORT) {
            printf("%d\n", *VAL);
            // Increments here should be reflected outside this PID.
            *VAL = *VAL + 1;
            usleep(1000000);
        }
        exit(0);
    } else {
        app = gtk_application_new ("org.gtk.example", G_APPLICATION_FLAGS_NONE);
        // The passing line
        g_signal_connect (app, "activate", G_CALLBACK (activate), VAL);
        status = g_application_run (G_APPLICATION (app), argc, argv);
        g_object_unref (app);
        *ABORT = 1;
    }
    *ABORT = 1;
    return status;
}

运行时会发生什么

当 MWE 运行时，终端会尽职尽责地在每次更新时打印该值。然而，GTK 窗口永远显示“val: 1”。我们可以通过在activate 进程中的gtk_widget_show_all 之前添加usleep(3000000) 来告诉GTK 进程可以访问存储在mmap 中的值。在此变体中，窗口将永远显示“val: 4”。

重申的问题

如何使 GTK 窗口上的输出与终端匹配？

Answer 1

那是因为activate 只被调用一次（当窗口被加载/激活时）但加载后没有刷新标签，我在代码中做了一些更改（使用全局，非常难看但很简单来说明问题)，“退出按钮”现在是“刷新按钮”。按下它，你会看到VAL的变化。

/*
 * Update GTK label from variable stored in mmap
 */

#include <stdlib.h>
#include <unistd.h>
#include <sys/mman.h>
#include <gtk/gtk.h>

static GtkWidget *text_status;

static void refresh(GtkWidget *widget, gpointer data)
{
    (void)widget;

    char msg[32]={0};

    g_snprintf(msg, sizeof msg, "val: %d\n", *(int *)data);
    gtk_label_set_text(GTK_LABEL(text_status), msg);
}

static void activate (GtkApplication *app, gpointer localval) {
    GtkWidget *window;
    // Button Containers
    GtkWidget *button_box_quit;
    // Buttons
    GtkWidget *refresh_button;
    // Text


    // Define Window, dynamic size for screen.
    window = gtk_application_window_new (app);
    gtk_window_set_title (GTK_WINDOW (window), "test");
    gtk_window_set_default_size(GTK_WINDOW(window), 400, 300);

    // Define Button Boxes.
    button_box_quit = gtk_button_box_new(GTK_ORIENTATION_HORIZONTAL);



    // Define Exit Button, put it in a box, put box in window
    refresh_button = gtk_button_new_with_label ("Refresh");
    gtk_container_add(GTK_CONTAINER (button_box_quit), refresh_button);
    gtk_container_add(GTK_CONTAINER (window), button_box_quit);

    // Connect signals to buttons
    g_signal_connect(refresh_button, "clicked", G_CALLBACK (refresh), localval);

    // Define text status
    char msg[32]={0};
    // The "print" line
    g_snprintf(msg, sizeof msg, "val: %d\n", *(int *)localval);
    text_status = gtk_label_new(msg);
    gtk_container_add(GTK_CONTAINER (button_box_quit), text_status);

    //Activate!
    g_snprintf(msg, sizeof msg, "val: %d\n", *(int *)localval);
    gtk_label_set_text(GTK_LABEL(text_status), msg);
    gtk_widget_show_all (window);
}

int main (int argc, char **argv) {
    GtkApplication *app;
    int status;

    int *VAL = mmap(NULL, sizeof(int), PROT_READ|PROT_WRITE, MAP_SHARED|MAP_ANONYMOUS, -1, 0);
    int *ABORT = mmap(NULL, sizeof(int), PROT_READ|PROT_WRITE, MAP_SHARED|MAP_ANONYMOUS, -1, 0);
    int pid = fork();

    if (pid == 0) {
        while(!*ABORT) {
            printf("%d\n", *VAL);
            // Increments here should be reflected outside this PID.
            *VAL = *VAL + 1;
            usleep(1000000);
        }
        exit(0);
    } else {
        app = gtk_application_new ("org.gtk.example", G_APPLICATION_FLAGS_NONE);
        // The passing line
        g_signal_connect (app, "activate", G_CALLBACK (activate), VAL);
        status = g_application_run (G_APPLICATION (app), argc, argv);
        g_object_unref (app);
        *ABORT = 1;
    }
    *ABORT = 1;
    return status;
}

如果你想在不按按钮的情况下刷新标签，可以使用g_timeout_add并设置一个函数定期调用刷新VAL。

Answer 2

g_timeout_add解决方案

如@David Ranieri 指出的，为了允许从应用程序自动更新主循环，我们可以使用g_timeout_add。但是，GTK3 的 API 要求我们将 refresh 函数传递给 g_timeout_add 略有不同。

修改 OP MWE 和@David Ranieri 的回答：

/*
 * Update GTK label from variable stored in mmap
 * Timeout Method
 */

#include <stdlib.h>
#include <unistd.h>
#include <sys/mman.h>
#include <gtk/gtk.h>

static GtkWidget *text_status;

static gboolean refresh(gpointer data) {
    char msg[32]={0};

    g_snprintf(msg, sizeof msg, "val: %d\n", *(int *)data);
    gtk_label_set_text(GTK_LABEL(text_status), msg);

    return TRUE;
}

static void activate (GtkApplication *app, gpointer localval) {
    GtkWidget *window;
    // Button Containers
    GtkWidget *button_box_quit;
    // Buttons
    GtkWidget *exit_button;

    // Define Window, dynamic size for screen.
    window = gtk_application_window_new (app);
    gtk_window_set_title (GTK_WINDOW (window), "test");
    gtk_window_set_default_size(GTK_WINDOW(window), 400, 300);

    // Define Button Boxes.
    button_box_quit = gtk_button_box_new(GTK_ORIENTATION_HORIZONTAL);

    // Define Exit Button, put it in a box, put box in window
    exit_button = gtk_button_new_with_label ("Exit");
    gtk_container_add(GTK_CONTAINER (button_box_quit), exit_button);
    gtk_container_add(GTK_CONTAINER (window), button_box_quit);

    // Connect signals to buttons
    g_signal_connect_swapped (exit_button, "clicked", G_CALLBACK (gtk_widget_destroy), window);

    // Define text status
    text_status = gtk_label_new(NULL);
    gtk_container_add(GTK_CONTAINER (button_box_quit), text_status);

    // Define timeout
    g_timeout_add(500, G_SOURCE_FUNC(refresh), localval);

    // Activate!
    refresh(localval);
    gtk_widget_show_all (window);
}

int main (int argc, char **argv) {
    GtkApplication *app;
    int status;

    int *VAL = mmap(NULL, sizeof(int), PROT_READ|PROT_WRITE, MAP_SHARED|MAP_ANONYMOUS, -1, 0);
    int *ABORT = mmap(NULL, sizeof(int), PROT_READ|PROT_WRITE, MAP_SHARED|MAP_ANONYMOUS, -1, 0);
    int pid = fork();

    if (pid == 0) {
        while(!*ABORT) {
            printf("%d\n", *VAL);
            // Increments here should be reflected outside this PID.
            *VAL = *VAL + 1;
            usleep(1000000);
        }
        exit(0);
    } else {
        app = gtk_application_new ("org.gtk.example", G_APPLICATION_FLAGS_NONE);
        // The passing line
        g_signal_connect (app, "activate", G_CALLBACK (activate), VAL);
        status = g_application_run (G_APPLICATION (app), argc, argv);
        g_object_unref (app);
        *ABORT = 1;
    }
    *ABORT = 1;
    return status;
}

重要的区别：

• 我们不再像使用回调时那样传递空小部件来刷新。
• 必须明确告知 GTK3 refresh 是 G_SOURCE_FUNC。