[LLVMdev] getElapsedWallTime unnecessary heap allocation and memory leak

[Bryan Keiren]

I’m not involved with however our threading is implemented or used ;) All I know is that we’re trying to match each allocation with a de-allocation and the way the LLVM code currently works is not compatible with this philosophy. Because we felt this might have been an issue with LLVM itself we decided to go here and ask you guys.

We will probably just patch LLVM locally (argh, I can already hear the muttered curses of the people who have to re-patch a future version upgrade… Haha).


From: Kostya Serebryany [mailto:kcc at google.com]
Sent: Wednesday, March 19, 2014 15:29
To: Bryan Keiren
Cc: Caldarale, Charles R; llvmdev at cs.uiuc.edu
Subject: Re: [LLVMdev] getElapsedWallTime unnecessary heap allocation and memory leak



On Wed, Mar 19, 2014 at 6:18 PM, Bryan Keiren <bryan.keiren at guerrilla-games.com<mailto:bryan.keiren at guerrilla-games.com>> wrote:
We are indeed trying to completely clean the heap before exiting main().

Which means that you either don't have threads, or you join all threads before main exits.
Is that the case?
Good for you if so!



-----Original Message-----
From: Caldarale, Charles R [mailto:Chuck.Caldarale at unisys.com<mailto:Chuck.Caldarale at unisys.com>]
Sent: Wednesday, March 19, 2014 14:42
To: Bryan Keiren; llvmdev at cs.uiuc.edu<mailto:llvmdev at cs.uiuc.edu>
Subject: RE: [LLVMdev] getElapsedWallTime unnecessary heap allocation and memory leak

> From: llvmdev-bounces at cs.uiuc.edu<mailto:llvmdev-bounces at cs.uiuc.edu> [mailto:llvmdev-bounces at cs.uiuc.edu<mailto:llvmdev-bounces at cs.uiuc.edu>]
> On Behalf Of Bryan Keiren
> Subject: [LLVMdev] getElapsedWallTime unnecessary heap allocation and
> memory leak

> In the file \lib\Support\Process.cpp on line 60, it seems as though an
> unnecessary heap allocation and memory leak occurs.

> static TimeValue getElapsedWallTime() {
>  static TimeValue &StartTime = *new TimeValue(TimeValue::now());
>  return TimeValue::now() - StartTime;
> }

> The issue is that the StartTime variable's value is allocated on the
> heap, after which a *reference* to it is stored (not the pointer
> itself). This means that the allocated memory is actually never properly de-allocated.

Since the StartTime field is static, why is this considered a leak?  The reference has not been lost and is utilized whenever getElapsedWallTime() is invoked.  Although it might be infinitesimally more efficient to avoid the new operator, the overall memory consumption is almost identical.

Are you trying to get rid of the entire heap at some point before process termination?

 - Chuck


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