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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">Hi Alexey,<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">The reason why our code considers this a leak is because just before termination of the application, our memory management code checks to see if there have
been any allocations that have not yet been matched with a de-allocation. Because we have overloaded the
<i>new</i> operator, the allocation of this variable passes through our own memory allocation routines and therefore is considered by the system when checking for leaks.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">I can see how this would not need to be considered a leak, as the memory is available to be used for the entire program execution. However, if you’re trying
to clean the entire heap before your application terminates (something we like to think isn’t such a far-fetched goal), then this allocation is an issue.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">I also understand your point regarding the dangers of having a function local static as in the code I proposed earlier.<o:p></o:p></span></p>
<p class="MsoNormal" style="margin-top:12.0pt"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">Would you say that in this case there is no way to ensure a fully cleaned heap before
<i>main()</i> exits without changing our definition of a memory leak?<o:p></o:p></span></p>
<p class="MsoNormal" style="margin-top:12.0pt"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">Cheers,<o:p></o:p></span></p>
<p class="MsoNormal" style="margin-top:12.0pt"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">Bryan<o:p></o:p></span></p>
<p class="MsoNormal"><a name="_MailEndCompose"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"><o:p> </o:p></span></a></p>
<p class="MsoNormal"><b><span style="font-size:10.0pt;font-family:"Tahoma","sans-serif"">From:</span></b><span style="font-size:10.0pt;font-family:"Tahoma","sans-serif""> Alexey Samsonov [mailto:samsonov@google.com]
<br>
<b>Sent:</b> Wednesday, March 19, 2014 14:46<br>
<b>To:</b> Bryan Keiren<br>
<b>Cc:</b> llvmdev@cs.uiuc.edu<br>
<b>Subject:</b> Re: [LLVMdev] getElapsedWallTime unnecessary heap allocation and memory leak<o:p></o:p></span></p>
<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">Hi Bryan,<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">On Wed, Mar 19, 2014 at 5:17 PM, Bryan Keiren <<a href="mailto:bryan.keiren@guerrilla-games.com" target="_blank">bryan.keiren@guerrilla-games.com</a>> wrote:<o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="font-family:"Arial","sans-serif";color:#222222;background:white">In the file \lib\Support\Process.cpp on line 60, it seems as though an unnecessary heap allocation
and memory leak occurs.</span><o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="font-family:"Arial","sans-serif";color:#222222"> </span><o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="font-family:"Arial","sans-serif";color:#222222">This is the offending code:</span><o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="font-family:"Arial","sans-serif";color:#222222"> </span><o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><i><span style="font-family:"Arial","sans-serif";color:#222222">static TimeValue getElapsedWallTime() {</span></i><o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><i><span style="font-family:"Arial","sans-serif";color:#222222"> static TimeValue &StartTime = *new TimeValue(TimeValue::now());</span></i><o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><i><span style="font-family:"Arial","sans-serif";color:#222222"> return TimeValue::now() - StartTime;</span></i><o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><i><span style="font-family:"Arial","sans-serif";color:#222222">}</span></i><o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="font-family:"Arial","sans-serif";color:#222222"> </span><o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="font-family:"Arial","sans-serif";color:#222222">The issue is that the <i>StartTime</i> variable's value is allocated on the heap, after which a *<b>reference</b>* to
it is stored (not the pointer itself). This means that the allocated memory is actually never properly de-allocated. </span><o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">What is the difference between storing a pointer and a reference here?<o:p></o:p></p>
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<p class="MsoNormal"> <o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="font-family:"Arial","sans-serif";color:#222222">Granted, the memory leak is small but if anyone attempts to write memory leak-free software while including LLVM code,
this will be an issue (as it currently is for our company).</span><o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="font-family:"Arial","sans-serif";color:#222222"> </span><o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="font-family:"Arial","sans-serif";color:#222222"> </span><o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="font-family:"Arial","sans-serif";color:#222222">Is there anyone who knows why exactly this was implemented the way it currently is implemented? It seems rather unnecessary
to be implemented with this complexity when a simpler implementation would work as well:</span><o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="font-family:"Arial","sans-serif";color:#222222"> </span><o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><i><span style="font-family:"Arial","sans-serif";color:#222222">static TimeValue getElapsedWallTime() {</span></i><o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><i><span style="font-family:"Arial","sans-serif";color:#222222"> static TimeValue TimeValue(TimeValue::now());</span></i><o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><i><span style="font-family:"Arial","sans-serif";color:#222222"> return TimeValue::now() - StartTime;</span></i><o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><i><span style="font-family:"Arial","sans-serif";color:#222222">}</span></i><o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">Function-local static variables might be dangerous and lead to destruction-order problems. For example, if a program calls getElapsedWallTime() at destruction time (after main() exits), then static variable TimeValue might already<o:p></o:p></p>
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<p class="MsoNormal">be destroyed/deallocated. Memory pointed to by StartValue will most likely be considered as "reachable" until the end of the program, and shouldn't cause error reports by leak detectors, such as LeakSanitizer, for instance (<a href="http://clang.llvm.org/docs/LeakSanitizer.html">http://clang.llvm.org/docs/LeakSanitizer.html</a>)<o:p></o:p></p>
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<p class="MsoNormal"> <o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"> <o:p></o:p></p>
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<p class="MsoNormal" style="margin-bottom:12.0pt"><br>
_______________________________________________<br>
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http://llvm.cs.uiuc.edu</a><br>
<a href="http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev" target="_blank">http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev</a><o:p></o:p></p>
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<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">-- <o:p></o:p></p>
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<p class="MsoNormal">Alexey Samsonov, MSK<o:p></o:p></p>
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