- 什么是分布式系统
- 为什么需要分布式系统
- 通过并行来增加计算能力
- 通过备份来增加容错能力
- ...
- 为什么需要学习分布式系统
- 解决问题
- 不同场景下的技术方案选型
- debug
- 分布式系统的目标: 隐藏分布式带来的复杂度
- 让没有任何并发编程和分布式系统经验的程序员也可以使用分布式系统的资源
- 分布式系统主要的问题
- 性能: 水平扩展, Nx servers -> Nx total throughput
- MapReduce
The "ignore" command will reply "NOT_IGNORED\r\n" if the client attempts to ignore the only tube in its watch list.
- java
- python
- Add signal handler:
signal.signal(signal.SIGALRM, handler) - Stop threads using Event
class App:
def __init__(self):
self._stop = threading.Event()
def worker(self):
while not self._stop.is_set():
...
def stop(self):
self._stop.set()- 应用场景
- 显式确保某个类的对象有且仅有一个
- 实现方式
- 将构造函数声明为私有成员函数，创建一个静态方法来进行对象的创建
- How to implement a configurable singleton?
@staticmethodvs@classmethod
guava caches给出了in-memory cache的典型应用方式
- From a CacheLoader
- From a Callable
- Inserted Directly
- java
- golang
- python
- Reference Variables are not boxes, it's better to think of them as labels attached to objects.
- Identity, Equality, Aliases
- python
==means equalityismeans identity
- python
- Copies Are Shallow by Default
“In Python, there is no way to create private variables like there is with the private modifier in Java.”
“An interface seen as a set of methods to fulfill a role is what Smalltalkers called a procotol”
“Protocols are interfaces, but because they are informal—defined only by documentation and conventions—protocols cannot be enforced like formal interfaces can”
“A protocol may be partially implemented in a particular class, and that’s OK”
- testable