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mixed usage of lock protection and lock-free List template class in thread.h
- From: "Xiaofeng Liu via cygwin" <cygwin at cygwin dot com>
- To: The Cygwin Mailing List <cygwin at cygwin dot com>
- Date: Fri, 1 Dec 2017 16:45:09 +0000 (UTC)
- Subject: mixed usage of lock protection and lock-free List template class in thread.h
- Authentication-results: sourceware.org; auth=none
- References: <1543396632.5417641.1512146709346.ref@mail.yahoo.com>
- Reply-to: Xiaofeng Liu <liuxf09 at yahoo dot com>
- Reply-to: Xiaofeng Liu <liuxf09 at yahoo dot com>
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
Several strategies for implementing non-blocking lists have been suggested. | |
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