Threads in the new ISO C Standard from 2011

More documents

Recommendations

Info

Motivation for Dependency Ordering Improved performance! In programs (such as the Linux kernel) with important data structures which are rarely modified and very frequently read there exist faster solutions than using full release/acquire synchronization on modern architectures. In this sense modern architectures include Power, MIPS and ARM. For other architectures including x86, optimizing compilers can make better optimizations if dependency ordering is used rather than release/acquire, as we will see below. Jonas Skeppstedt (js@cs.lth.se) Lecture 6 2013 36 / 70
Read-Copy Update RCU is an alternative to readers-writers locks with the following essential functionality: Pointers to data structures are protected with RCU. Readers use read-side critical sections marked by enter/exit calls. When a reader is in such a section a writer may not modify the data structure but instead modifies a copy of it. When the last reader has left, the original data structure is updated. RCU is heavily used in the Linux kernel. RCU was one part of the SCO vs IBM lawsuit. From linux-2.6.37.1/kernel/signal.c /∗ ∗ Protect access to @t credentials . This can go away when all ∗ callers hold rcu read lock . ∗/ rcu_read_lock(); user = get_uid(__task_cred(t)->user); atomic_inc(&user->sigpending); rcu_read_unlock(); Jonas Skeppstedt (js@cs.lth.se) Lecture 6 2013 37 / 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 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: Inter-Thread Happens Before An eval
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

You also want an ePaper? Increase the reach of your titles

Delete template?

Save as template?