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Date: Fri, 1 Dec 2017 16:45:09 +0000 (UTC)
From: "Xiaofeng Liu via cygwin" <cygwin AT cygwin DOT com>
Reply-To: Xiaofeng Liu <liuxf09 AT yahoo DOT com>
Reply-To: Xiaofeng Liu <liuxf09 AT yahoo DOT com>
To: The Cygwin Mailing List <cygwin AT cygwin DOT com>
Message-ID: <1543396632.5417641.1512146709346@mail.yahoo.com>
Subject: mixed usage of lock protection and lock-free List template class in thread.h
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Lock protection and lock-free should never be mixed ! 
​https://cygwin.com/git/gitweb.cgi?p=newlib-cygwin.git;a=blob;f=winsup/cygwin/thread.h;hb=1f42dc2bcf58d3b8629eb13d53de3f69fc314b47#l110

 110 template <class list_node> inline void 111 List_insert (list_node *&head, list_node *node) 112 { 113   if (!node) 114     return; 115   do 116     node->next = head; 117   while (InterlockedCompareExchangePointer ((PVOID volatile *) &head, 118                                             node, node->next) != node->next); 119 } 120  121 template <class list_node> inline void 122 List_remove (fast_mutex &mx, list_node *&head, list_node *node) 123 { 124   if (!node) 125     return; 126   mx.lock (); 127   if (head) 128     { 129       if (InterlockedCompareExchangePointer ((PVOID volatile *) &head, 130                                              node->next, node) != node) 131         { 132           list_node *cur = head; 133  134           while (cur->next && node != cur->next) 135             cur = cur->next; 136           if (node == cur->next) 137             cur->next = cur->next->next; 138         } 139     } 140   mx.unlock (); 141 }
The symptom I met is a job hang with the following stack:
#0  0x000000007711c2ea in ntdll!ZwWaitForMultipleObjects () from /cygdrive/c/Windows/SYSTEM32/ntdll.dll
#1  0x000007fefd111430 in KERNELBASE!GetCurrentProcess () from /cygdrive/c/Windows/system32/KERNELBASE.dll
#2  0x0000000076fc06c0 in WaitForMultipleObjects () from /cygdrive/c/Windows/system32/kernel32.dll
#3  0x00000001800458ac in cygwait(void*, _LARGE_INTEGER*, unsigned int) () from /usr/bin/cygwin1.dll
#4  0x000000018013d029 in pthread_cond::~pthread_cond() () from /usr/bin/cygwin1.dll
#5  0x000000018013d0dd in pthread_cond::~pthread_cond() () from /usr/bin/cygwin1.dll
#6  0x0000000180141196 in pthread_cond_destroy () from /usr/bin/cygwin1.dll
#7  0x0000000180116d5b in _sigfe () from /usr/bin/cygwin1.dll
#8  0x0000000100908e38 in std::_Sp_counted_ptr_inplace<std::__future_base::_Task_state<std::function<void ()>, std::allocator<int>, void ()>, std::allocator<int>, (__gnu_cxx::_Lock_policy)2>::_M_dispose() ()
The problem with the current implementation for concurrent insert and delete is explained at WikipediaNon-blocking linked list

My question is how to solve this ? Adding lock protection in List_insert (removing lock-freee) or implementing a complete lock-free List based on Harris's solution to use two CAS?
Thanks.
Xiaofeng Liu

  
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Non-blocking linked list
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