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<P>Hello Eric,</P>
<P> </P>
<P>Thank you for the reply.</P>
<P> </P>
<P>If it is intentionally leaked, Is it freed at any later stage and who is responsible for cleanup?</P>
<P> </P>
<P>In our case, below is the call sequence.</P>
<P> </P>
<P>======================<STRONG>First Time(No Memory Leak) </STRONG>============================== <BR>1. malloc() // ALLOC1 <BR> <BR>2. malloc() // ALLOC2 <BR> <BR>3. malloc() // ALLOC3 <BR> <BR>4. pthread_create() // pthread_create by std::thread <BR> <BR><STRONG>5. pthread_key_create() // Key created <BR> <BR>6. _aeabi_atexit() // static storage destructor register to atexit </STRONG><BR> <BR>7. free() //ALLOC3 freed <BR> <BR>8. pthread_exit() <BR> <BR><STRONG>9. std::__thread_specific_ptr<std::__thread_struct>::__at_thread_exit() <BR> //Key destructor called <BR> <BR>10. free() //ALLOC2 freed <BR> <BR>11. free() //ALOOC1 freed </STRONG><BR> <BR>12. std::__thread_specific_ptr<std::__thread_struct>::~__thread_specific_ptr <BR> //thread_specific_ptr static storage destructor called <BR> <BR>======================<STRONG>Second Time Onwards (Memory Leak)</STRONG> ======================= <BR>1. malloc() // ALLOC1 <BR> <BR>2. malloc() // ALLOC2 <BR> <BR>3. malloc() // ALLOC3 <BR> <BR>4. pthread_create() // pthread_create by std::thread <BR> <BR>5. free() //ALLOC3 free'd <BR> <BR>6. pthread_exit() </P>
<P> // ALLOC1 & ALLOC2 are not freed</P>
<P> // No call to __thread_specific_ptr destructor <BR>============================================================================== </P>
<P> </P>
<P>If we observe in the leak case, thread key is not created and<STRONG> </STRONG>static storage destructor is not registered to atexit. Hence there is no<STRONG> </STRONG>key destructor(::__at_thread_exit()) called during exit and ALLOC1 & ALLOC2 are not freed which were freed properly in the working case.</P>
<P>Also there is no call to __thread_specific_ptr destructor.</P>
<P>Note : As TizenRT is a RTOS and works on flat memory model, global data space(data & bss) are not released when application exits. Hence any variables with global scope always persist till the device power off.</P>
<P> </P>
<P>Can you please suggest some methods to avoid these leaks.?</P>
<P> </P>
<P>Thanks,</P>
<P>Manohar</P>
<P>--------- <B>Original Message</B> ---------</P>
<P><B>Sender</B> : Eric Fiselier <eric@efcs.ca></P>
<P><B>Date</B> : 2018-05-19 12:30 (GMT+5:30)</P>
<P><B>Title</B> : Re: [cfe-dev] [Libcxx/TizenRT]: Memory leak in std::thread</P>
<P> </P>
<DIV dir=ltr><BR>
<DIV class=gmail_extra><BR>
<DIV class=gmail_quote>On Fri, May 18, 2018 at 4:39 AM, Manohara Hosakoppa Krishnamurt via cfe-dev <SPAN dir=ltr><<A href="mailto:cfe-dev@lists.llvm.org" target=_blank>cfe-dev@lists.llvm.org</A>></SPAN> wrote:<BR>
<BLOCKQUOTE class=gmail_quote style="PADDING-LEFT: 1ex; MARGIN: 0px 0px 0px 0.8ex; BORDER-LEFT: #ccc 1px solid">
<DIV>
<P>Hello Everyone,</P>
<P> </P>
<P>We are using <STRONG>LLVM libc++ </STRONG>in TizenRT IoT OS( <A href="https://github.com/Samsung/TizenRT" target=_blank>https://github.com/Samsung/<WBR>TizenRT</A>). We observed <STRONG>memory leak while using std::thread</STRONG></P>
<P> </P>
<P>About TizenRT:</P>
<P>LLVM libc++ source has been integrated to TizenRT and the whole platform(OS + libc + libcpp + App) is built into a single elf executable.</P>
<P>TizenRT uses a FLAT memory model(physical memory), there is no virtual memory support and hence we cant run application executables (elf) directly.</P>
<P> </P>
<P>First time when we create a thread using std::thread , there is no memory leak after thread exits.</P>
<P>But next time onwards, if we create a thread using std::thread and after thread exits there is a memory leak.</P>
<P> </P>
<P>First time__thread_specific_ptr<__<WBR>thread_struct> is constructed in __thread_local_data() and hence the pthread_key_create() and during exit key is destroyed.</P>
<P> </P>
<P>But second time onwards, __thread_specific_ptr<__<WBR>thread_struct> is not getting constructed in __thread_local_data().</P>
<P>__thread_local_data() <WBR> <WBR> <BR>{ <WBR> <WBR> <BR> static __thread_specific_ptr<__<WBR>thread_struct> __p; <BR> return __p; <WBR> <WBR> <BR>}</P>
<P> </P>
<P>We suspect that the problem is with __thread_local_data(), and __thread_specific_ptr is getting constructed only once.</P>
<P>Because of this we feel "__thread_struct and __thread_struct_impl " which are allocated earlier during thread create are not getting freed and there is a leak.</P></DIV></BLOCKQUOTE>
<DIV>
<DIV style="FONT-SIZE: small; FONT-FAMILY: arial,sans-serif; WHITE-SPACE: normal; WORD-SPACING: 0px; TEXT-TRANSFORM: none; FONT-WEIGHT: 400; COLOR: rgb(34,34,34); FONT-STYLE: normal; LETTER-SPACING: normal; BACKGROUND-COLOR: rgb(255,255,255); TEXT-INDENT: 0px; font-variant-ligatures: normal; font-variant-caps: normal; text-decoration-style: initial; text-decoration-color: initial"><BR class=gmail-Apple-interchange-newline>__thread_specific_ptr intentionally leaks. See <A href="https://github.com/llvm-mirror/libcxx/blob/master/include/thread#L189">https://github.com/llvm-mirror/libcxx/blob/master/include/thread#L189</A></DIV> </DIV>
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<P> </P>
<P>Please guide us with, how can we deallocate these objects after or during thread exit.</P>
<P>Also what is the expected behavior of thread_local_data instance?<BR>1. One thread_local_data instance for a process/task and all of its threads(pthreads) share the same thread_local_data instance?</P>
<P>OR<BR>2. Each thread(pthread) should have a separate thread_local_data instance?</P>
<P> </P>
<P>Thanks,</P>
<P>Manohar</P>
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