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BSTR memory leaks #5184

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nvaccessAuto opened this issue Jun 26, 2015 · 6 comments
Closed

BSTR memory leaks #5184

nvaccessAuto opened this issue Jun 26, 2015 · 6 comments
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bug/memory-leak bug

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@nvaccessAuto
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Reported by DelRed on 2015-06-26 09:10
Hello, I use UI Automation with my controls, I have noticed that when I use NVDA and just tab all controls on my form - it cases memory leaks in my application. If I use JAWS - there is no such problem.
I think that the issue is that when I return VARIANT with BSTR (for example as answer to UIA_NamePropertyId), or just BSTR (IValueProvider::get_Value(BSTR *pRetVal)) I use SysAllocString, so after NVDA use this BSTR it should call SysFreeString.
@nvaccessAuto
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Comment 2 by jteh on 2015-06-26 12:01
What makes you suspect BSTR allocation as opposed to, say, holding UI Automation elements? NVDA accesses UI Automation out-of-process, so the string in your process is probably freed by COM after it is marshaled, rather than when NVDA frees it.

Also, do you see these leaks when you use Narrator? The way NVDA consumes UIA is probably more similar to Narrator.

@nvaccessAuto
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Comment 3 by DelRed (in reply to comment 2) on 2015-06-26 13:00
Replying to jteh:

What makes you suspect BSTR allocation as opposed to, say, holding UI Automation elements? NVDA accesses UI Automation out-of-process, so the string in your process is probably freed by COM after it is marshaled, rather than when NVDA frees it.

Also, do you see these leaks when you use Narrator? The way NVDA consumes UIA is probably more similar to Narrator.

There are no leaks when I use Narrator.
I suspect BSTR allocation, because it it the only thing that I allocate in my providers. And memory leaks when I simply circle through controls (I just hold Tab). I see it like this: NVDA ask for element's name, I allocate string, but it is not freed then.

@nvaccessAuto
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Comment 4 by jteh on 2015-06-28 23:08
You (or at least UI Automation) would also be allocating instances of UIA elements.

Ctypes/comtypes manages freeing of BSTR in NVDA. We actually had to work around a bug a while ago where ctypes/comtypes was calling SysFreeString twice in certain cases. I don't think this is related, but I could be missing something. Mick may have a better idea on this one, but he's away for a couple of weeks.

It'd be great if you can provide a simple compiled test case that shows this behaviour.

@nvaccessAuto
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Comment 5 by mdcurran on 2015-09-10 04:56
Windows does not free BSTRs straight away by default. To ensure memory is really not being freed, set the OANOCACHE environment variable to 1 before testing your app.
But as mentioned above, without a testcase we cannot debug this any further.

@jcsteh jcsteh removed the Untriaged label Nov 13, 2015
@LeonarddeR
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Although a very interesting ticket, I'm afraid we can't contact the original author any more, and as @michaelDCurran stated in #5184 (comment), a test case is needed for this. I'm leaning towards a close.

@ehollig
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ehollig commented Oct 13, 2018

Closing, as suggested by @LeonarddeR in #5184 (comment)

@ehollig ehollig closed this as completed Oct 13, 2018
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