Can't seem to shutdown cef process

[aleitner]

Code: Select all

typedef struct _shutdown_task {
    cef_task_t task;
    int ref_count;
} shutdown_task_t;

[aleitner]

I've tried updating to use atomic_int but that didn't seem to help

Task Structure

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typedef struct _shutdown_task {
    cef_task_t task;
    atomic_int  ref_count;
} shutdown_task_t;


Add Ref callback

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static void CEF_CALLBACK add_ref_shutdown_task(struct _cef_base_ref_counted_t* base) {
    /**
     * The shutdown_task to be referenced. Convert from base structure to our wrap structure
     */
    shutdown_task_t* task = (shutdown_task_t*)base;

    if (task == NULL)
        return;

    fprintf(stderr, "add_ref_shutdown_task.\n");

    /* increment the reference count */
    atomic_fetch_add(&task->ref_count, 1);
}


Release Callback

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static int CEF_CALLBACK release_shutdown_task(struct _cef_base_ref_counted_t* base) {
    shutdown_task_t* task = (shutdown_task_t*)base;

    fprintf(stderr, "release_shutdown_task.\n");

    if ( atomic_fetch_sub(&task->ref_count, 1) == 1) {
        free(task);
        task = NULL;
        return 1;
    }
   
    return 0;
}


has_one_ref Callback

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static int CEF_CALLBACK has_one_ref(struct _cef_base_ref_counted_t* base) {
    shutdown_task_t* task = (shutdown_task_t*)base;

    return task->ref_count == 1 ? 1 : 0;
}

execute Callback

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static void CEF_CALLBACK shutdown_execute(struct _cef_task_t* task) {
    fprintf(stderr, "shutdown.\n");
    cef_quit_message_loop();
}


Initialize task

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shutdown_task_t* create_shutdown_task() {
    shutdown_task_t* task = (shutdown_task_t*)calloc(1, sizeof(shutdown_task_t));

    task->task.base.size = sizeof(shutdown_task_t);
    task->task.base.add_ref = add_ref_shutdown_task;
    task->task.base.release = release_shutdown_task;
    task->task.base.has_one_ref = has_one_ref;
    task->task.execute = shutdown_execute;
    task->ref_count = 1;

    return task;
}


Post Task

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shutdown_task_t* task = create_shutdown_task();
cef_post_task(TID_UI, &task->task);


[magreenblatt]

I usually see
add_ref_shutdown_task.
release_shutdown_task.
free(): invalid pointer

This is strange, because the reference count in your code starts at 1. So I would expect the free() after 2 calls to release_shutdown_task.

[aleitner]

I usually see
add_ref_shutdown_task.
release_shutdown_task.
free(): invalid pointer

This is strange, because the reference count in your code starts at 1. So I would expect the free() after 2 calls to release_shutdown_task.

I assume something is crashing before all the stderr prints.

Sometimes it does succeed and we see

add_ref_shutdown_task.
release_shutdown_task.
add_ref_shutdown_task.
release_shutdown_task.
shutdown.
release_shutdown_task.

[magreenblatt]

Sometimes it does succeed and we see

add_ref_shutdown_task.
release_shutdown_task.
add_ref_shutdown_task.
release_shutdown_task.
shutdown.
release_shutdown_task.

That looks correct to me.

[ndesktop]

Code: Select all

// release
static int CEF_CALLBACK release_shutdown_task(struct _cef_base_ref_counted_t* base) {
    shutdown_task_t* task = (shutdown_task_t*)base;

    fprintf(stderr, "release_shutdown_task.\n");

    --task->ref_count;
   
    if (task->ref_count == 0) {
        if (task)
            free(task);       
        return 1;
    }
   
    return 0;
}


I'm not familiar with the C convention of addref/release in CEF (but I suppose is similar with what COM does), but shouldn't release return 0 when task->ref_count is 0 (and frees), and task->ref_count when it is > 0?
Something like this:

Code: Select all

static int CEF_CALLBACK release_shutdown_task(struct _cef_base_ref_counted_t* base) {
    shutdown_task_t* task = (shutdown_task_t*)base;
    int ref = --task->ref_count;
    if (ref == 0) {
        if (task)
            free(task);       
        return 0;
    }
    return ref;
}


[aleitner]

https://github.com/chromiumembedded/cef ... capi.h#L61

Returns true (1) if the resulting reference count is 0.

And of course after I posted that it has yet to encounter any double free errors again. It all seems to be working. I am still curious on what the advantage of implementing reference counting is over just manually calling free()

With reference counting

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shutdown_task_t* task = create_shutdown_task();
cef_post_task(TID_UI, &task->task);

vs
Without reference counting

Code: Select all

shutdown_task_t* task = create_shutdown_task();
cef_post_task(TID_UI, &task->task);
free(task);

[ndesktop]

Returns true (1) if the resulting reference count is 0.

Yes, I saw that after posting.
Maybe is something related to has_one_ref? I noticed you use atomic_ for addref and release, but a simple == 1 on has_one_ref.
Perhaps atomic_compare_exchange_strong ?

[magreenblatt]

I am still curious on what the advantage of implementing reference counting is over just manually calling free()

If was the easiest way to manage object lifespan across multiple threads, delegates, etc. If we were to redesign the CEF API today (very unlikely) we might choose a more explicit form of lifespan management.