CachingFlowManager这部分为Azkaban在管理job中cache管理这一部分。

[java] 、
public CachingFlowManager(FlowManager baseManager, final int cacheSize)
{
this.baseManager = baseManager;

this.flowCache = Collections.synchronizedMap(
new LinkedHashMap((int) (cacheSize * 1.5), 0.75f, true){
@Override
protected boolean removeEldestEntry(Map.Entry eldest)
{
final boolean tooManyElements = super.size() > cacheSize;

if (tooManyElements) {
final Status status = eldest.getValue().getFlow().getStatus();

if (status != Status.RUNNING) {
return true;
}
else {
log.warn(String.format(
"Cache is at size[%s] and should have evicted an entry, but the oldest entry wasn't completed[%s]. Perhaps the cache size is too small",
super.size(),
status
));
}
}

return false;
}
}
);
}

public CachingFlowManager(FlowManager baseManager, final int cacheSize)
{
this.baseManager = baseManager;

this.flowCache = Collections.synchronizedMap(
new LinkedHashMap((int) (cacheSize * 1.5), 0.75f, true){
@Override
protected boolean removeEldestEntry(Map.Entry eldest)
{
final boolean tooManyElements = super.size() > cacheSize;

if (tooManyElements) {
final Status status = eldest.getValue().getFlow().getStatus();

if (status != Status.RUNNING) {
return true;
}
else {
log.warn(String.format(
"Cache is at size[%s] and should have evicted an entry, but the oldest entry wasn't completed[%s]. Perhaps the cache size is too small",
super.size(),
status
));
}
}

return false;
}
}
);
}

在这个方法中涉及到几个地方是之前没有学习到过、也没有遇到过的。

下面都一一来研究下。

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1、Collections.synchronizedMap

先来看下在JDK中对Collections的解释：

接下来synchronizedMap

顾名思义，synchronize是同步，那则为同步的map。

public static Map synchronizedMap(Map m) 这是一个返回由指定映射支持的同步（线程安全的）映射的方法。也就是返回一个线程安全的map

2、new LinkedHashMap((int) (cacheSize * 1.5), 0.75f, true)

LinkedHashMap是JDK1.4引入的新的集合类，相信很多人都没有用到过LinkedHashMap。

LinkedHashMap相当于是一个对HashMap的扩展，它在Hash的实现有加上了对Linked的支持。