Threads in the new ISO C Standard from 2011

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Mutex Unlock/Lock A mutex in C11 is called mtx_t int a; Thread 1 Thread 2 mtx_lock(&m); a = 1; mtx_unlock(&m); mtx_lock(&m); printf("a = %d\n", a); mtx_unlock(&m); The unlock by Thread 1 and lock by Thread 2 make the write of a visible to Thread 2. A part of the mutex unlock is to perform a release operation and of a mutex lock to perform an acquire operation. The write by Thread 1 is said to happen before the read by Thread 2. Jonas Skeppstedt (js@cs.lth.se) Lecture 6 2013 22 / 70
Release and Acquire, and Consume Recall, a release makes previous writes visible to other threads. A release orders memory accesses so that no preceding write may be moved to after the release by the compiler or hardware. An acquire makes writes by other threads that have made a release visible. An acquire orders memory accesses so that no subsequent read or write may be moved to before the acquire. A consume is similar to an acquire but it lets unrelated reads be moved by the compiler to before the consume. In addition it can be implemented faster on some machines including Power. Release/acquire is different from unlock/lock but unlock/lock perform release/aqcuire in addition to keeping track of the lock value. Jonas Skeppstedt (js@cs.lth.se) Lecture 6 2013 23 / 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 and 14: Atomic Compare and Exchange There a
Page 15 and 16: Weak Compare and Exchange Functions
Page 17 and 18: Atomic Fetch and Modify Functions T
Page 19 and 20: Atomic Flag The atomic flag type an
Page 21: The C11 Memory Consistency Model fo
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

Threads in the new ISO C Standard from 2011

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