Threads in the new ISO C Standard from 2011

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Atomic Compare and Exchange Function Prototypes bool atomic_compare_exchange_strong_explicit( volatile A* ptr, C* expected, C value, memory_order success, memory_order failure); bool atomic_compare_exchange_weak_explicit( volatile A* ptr, C* expected, C value, memory_order success, memory_order failure); bool atomic_compare_exchange_strong( volatile A* ptr, C* expected, C value); bool atomic_compare_exchange_weak( volatile A* ptr, C* expected, C value); For the explicit functions, memory is affected according to parameters success and failure, depending on the result of the comparison. Jonas Skeppstedt (js@cs.lth.se) Lecture 6 2013 14 / 70
Weak Compare and Exchange Functions The weak compare and exchange functions may fail spuriously, which means they fail to perform the compare and exchange and ”give up”. If so, the return value is guaranteed to be false, and the current value is not copied to what ptr points. The weak forms allow faster implementation on machines with load-locked/load-linked/load-and-reserve and store conditional instructions — instead of atomic compare and exchange. The load-locked type of instructions are described below but the ide and ta is to split the atomic operation into two instructions. A processor P first performs a load-locked and then a store conditional. If a different processor Q performs a store between the load-locked and store conditional made by P, then the store conditional made by P fails. Jonas Skeppstedt (js@cs.lth.se) Lecture 6 2013 15 / 70
Page 1 and 2: Threads in the new ISO C Standard f
Page 3 and 4: Atomic Objects Atomic objects are n
Page 5 and 6: Using Atomic Objects Members of an
Page 7 and 8: Lock Free Property To know whether
Page 9 and 10: Memory Order for Atomic Operations
Page 11 and 12: Answer: Yes The code may execute in
Page 13: Atomic Compare and Exchange There a
Page 17 and 18: Atomic Fetch and Modify Functions T
Page 19 and 20: Atomic Flag The atomic flag type an
Page 21 and 22: The C11 Memory Consistency Model fo
Page 23 and 24: Release and Acquire, and Consume Re
Page 25 and 26: Happens Before and Data Races We wi
Page 27 and 28: Sequenced Before The most common se
Page 29 and 30: An Example _Atomic int m; int u; //
Page 31 and 32: Dependences Dependences are intra-t
Page 33 and 34: Definition of Dependency in C11 A c
Page 35 and 36: Inter-Thread Happens Before An eval
Page 37 and 38: Read-Copy Update RCU is an alternat
Page 39 and 40: A Simplified Example Consider the f
Page 41 and 42: More Details About Dependences Reca
Page 43 and 44: Constant Propagation Example 2(3) T
Page 45 and 46: One More Data Dependency a = atomic
Page 47 and 48: Load and Reserve/Store Conditional
Page 49 and 50: Power Memory Barrier Instructions T
Page 51 and 52: lwsync Memory Barrier for Release O
Page 53 and 54: c;isync Memory Barrier for Load Acq
Page 55 and 56: Cumulative Ordering If the memory a
Page 57 and 58: Implementation on Power The followi
Page 59 and 60: Store Store relaxed st Store releas
Page 61 and 62: Acquire and Release a Spin Lock # a
Page 63 and 64: Initialization Function void call_o
Page 65 and 66:
Mutex Options for mtx_init Function
Page 67 and 68:
Condition Variable Functions int cn
Page 69 and 70:
Thread Functions int thrd_create(th
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Threads in the new ISO C Standard from 2011

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