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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