公司effective concurrency培训笔记 by Herb Sutter

三天的培训，第一天去发现讲师是个c++牛人：Herb Sutter，公司花了一个人2000多刀，感觉不是很值，废话少说，记点笔记先，也算是学过，以后用到也好reference下：

题目是《Effecitve Concurrency Introduction and Overview》

1. Three Pillars of Dawn

• Concurrency For Isolation : Responsiveness
• Parallelism For Scalability : Throughput, scalability
• Consistency By Synchronization : Race-fess, deadlock-free

2. Concurrency Fundamentals：

• A Few Good Primitives : Threads, pools, lambdas, futures, locks and atomics
• Think In Transactions : Exception safety, public functions, and locked blocks
• Habitually Prefer Structured/Bounded Lifetimes : Locks, tasks, and more
• Recognize and Avoid Today's Overheads : Switching, contention, the const of unrealized parallelism
• Understand the Ture Nature of Deadlock : locks + messages + I/O + any other blocking
• concurrency在server端好解决，在client端难解决。
• 未来的芯片趋势是Mixed large & small cores的多核系统。

3.  Active Object Pattern

• 使用Active Object来封装所有需要异步或者需要自己管理threads的地方
• Active Object可以用在GUI线程，decouple independent works，封装resources(I/O, shared objects)
• 需要实现一个Active Helper
• 当需要在Active Object返回值时可以使用“Out” parameters or send a message back

4. Machine Architecture, Performance and Scalability

• root of all hardware complexity : Latency (correctness + performance)
• Latency和Bandwidth : Bandwidth 可以用钱买，Latency有Limit
• 目前的瓶颈在于memory而不在CPU : int i = i1 + i2; double d = d1 * d2 需要的cost其实是一样的，大概都是15的cpu circles.因为14个circles都花在等momory上了
• Latency从少到多分别是Registers, L1 Cache, L2 Cache, Locak DRAM, Remote DRAM, Flash, Disk

5. How to Migrate Code to the Many Core “Free Lunch”

• Natural Parallelism ： Quicksort, trees, graphs, hash tables
• 好处 ：在多核上更快，充分利用多核
• Pay ：Races, deadlocks, cost vs sequential
• 基本的并行逻辑 ：Fork->Run->Join
• 了解 scalability ：不是核越多越快，需要考虑很多别的东西(memory, I/O)
• 选择合适的data structures ： 需要同时考虑Concurrency和Parallelization

6. How to stop threads

　　a. Kill : Thread.Abort (Avoid, almost sertain to corrupt transactions)

　　b. Tell and don't take no for an answer : pthread_cancel (Rudem only for languages without exceptions/unwind)

　　c. Ask : Thead.Interrupt (Better, but hard to use in practice)

　　d. Flag and let it poll (Best, though requres cooperative effort)

7. Consistency : Saft Locking

• Prefer scoped locking and always have objects own locks
• Avoid Races : Associated data with locks
• Avoid Deadlock : Apply lock hierarchies and other lock ordering
• Acoid Composability Problems : Don't call unknow code while holding a lock