UIAutomation FindAll泄漏内存

Question

The UIAutomation FindAll function leaks memory on my system even though array->Release is called. See "memory leak" in the example program below. I've done some searching around on stack overflow, and I've seen some comments about memory garbage collection taking about 3 minutes start working, but what I see is a memory leak. Note that the program below has no malloc or new. I'm using Windows 7 with Service Pack 1. cl version is: Microsoft (R) 32-bit C/C++ Optimizing Compiler Version 16.00.40219.01 for 80x86.

/* Program to demonstrate that IUIAutomation function FindAll leaks memory.
 * Build with: cl uia_memleak.cpp user32.lib ole32.lib oleaut32.lib 
 */

#include <windows.h>
#include <stdio.h>         /* for fprintf */
#include <assert.h>        /* for assert */
#include <UIAutomation.h>
#include <oleauto.h>


/* Forward declarations */
void loop_get_buttons(IUIAutomation * pui, HWND hwnd, int iterations);
int get_buttons(IUIAutomation * pui, HWND hwnd);
BOOL button_appender(IUIAutomation * pui, IUIAutomationElement * root);
BOOL button_condition_appender(IUIAutomation * pui, IUIAutomationElement * root, IUIAutomationCondition * condition);


int
main(int argc, char *argv[])
{
    int i;
    HRESULT hr;
    IUIAutomation *pui;

    CoInitialize(NULL);

    hr = CoCreateInstance(__uuidof(CUIAutomation), NULL, CLSCTX_INPROC_SERVER, __uuidof(IUIAutomation), (void **)&pui);
    assert(hr == S_OK);

    fprintf(stdout,
        "Open the Task Manager to observe the memory consumed by this program.  Press Enter and then open and select the calc program. You should see the Memory column increasing slowly.  This program will complete in under a minute.\n");
    getchar();

    for (i = 0; i < 100; i++) {
        HWND hwnd;
        hwnd = GetTopWindow(NULL);
        loop_get_buttons(pui, hwnd, 500);
    }

    fprintf(stdout, "Press Enter to quit.\n");
    getchar();
    CoUninitialize();
    return 0;
}


void
loop_get_buttons(IUIAutomation * pui, HWND hwnd, int iterations)
{
    int i;
    for (i = 0; i < iterations; i++) {
        get_buttons(pui, hwnd);
    }
}


int
get_buttons(IUIAutomation * pui, HWND hwnd)
{
    HRESULT hr;
    IUIAutomationElement *root = NULL;

    hr = pui->ElementFromHandle(hwnd, &root);
    assert(hr == S_OK);
    button_appender(pui, root);
    root->Release();
    return 0;
}


BOOL
button_appender(IUIAutomation * pui, IUIAutomationElement * root)
{
    /* Returns FALSE on success, TRUE on error. */
    HRESULT hr;
    VARIANT varProp;
    IUIAutomationCondition *condition;

    assert(root != NULL);

    varProp.vt = VT_I4;
    varProp.lVal = UIA_ButtonControlTypeId;
    hr = pui->CreatePropertyCondition(UIA_ControlTypePropertyId, varProp, &condition);
    assert(hr == S_OK && condition != NULL);

    button_condition_appender(pui, root, condition);
    condition->Release();
    VariantClear(&varProp);
    return FALSE;
}


BOOL
button_condition_appender(IUIAutomation * pui, IUIAutomationElement * root,
              IUIAutomationCondition * condition)
{
    /* Returns FALSE on success, TRUE on error. */
    HRESULT hr;
    IUIAutomationElementArray *array = NULL;

    assert(root);

    hr = root->FindAll(TreeScope_Descendants, condition, &array);    /* memory leak */
    assert(hr == S_OK);
    if (array)
        array->Release();
    return FALSE;
}

Answer 1

The following answer is an hypothesis:

• It is not sufficient to release the array->Release(); , but you'll have to release each element contained in the array separately.

The result of the findAll method is an IUIAutomationElementArray returned through the out-parameter array . array contains multiple IUIAutomationElement instances. All those instances have to be released.

PS: I found this post, because I was wondering whether the release of each element is necessary. Now because of your post I assume it is.