Java同步容器和并发容器详解

public class Test { static Vector vector = new Vector();
public static void main(String[] args) throws InterruptedException {
while(true) {
for (int i=0;i<10;i++)
vector.add(i);
Thread thread1 = new Thread(){
public void run() {
for (int i=0;i10) {
}
}
}
}

for (int i=0;i

for (int i=0;i

public class Test {
static Vector vector = new Vector();
public static void main(String[] args) throws InterruptedException {
while(true) {
for (int i=0;i<10;i++)
vector.add(i);
Thread thread1 = new Thread(){
public void run() {
synchronized (Test.class) {
//进行额外的同步
for (int i=0;i10) {
}
}
}
}

public class ConcurrentHashMap extends AbstractMap
implements ConcurrentMap, Serializable { // 将整个hashmap分成几个小的map，每个segment都是一个锁；与hashtable相比，这么设计的目的是对于put, remove等操作，可以减少并发冲突，对 // 不属于同一个片段的节点可以并发操作，大大提高了性能
final Segment[] segments;
// 本质上Segment类就是一个小的hashmap，里面table数组存储了各个节点的数据，继承了ReentrantLock, 可以作为互拆锁使用
static final class Segment extends ReentrantLock implements Serializable {
transient volatile HashEntry[] table;
transient int count;
}
// 基本节点，存储Key， Value值
static final class HashEntry {
final int hash;
final K key;
volatile V value;
volatile HashEntry next;
}
}

final V putVal(K key, V value, Boolean onlyIfAbsent) {
if (key == null || value == null) throw new NullPointerException();
int hash = spread(key.hashCode());
int binCount = 0;
for (Node[] tab = table;;) {
Node f;
int n, i, fh;
// 如果table为空，初始化；否则，根据hash值计算得到数组索引i，如果tab[i]为空，直接新建节点Node即可。注：tab[i]实质为链表或者红黑树的首节点。
if (tab == null || (n = tab.length) == 0)
tab = initTable(); else if ((f = tabAt(tab, i = (n - 1) & hash)) == null) {
if (casTabAt(tab, i, null, new Node(hash, key, value, null))) break;
// no lock when adding to empty bin
}
// 如果tab[i]不为空并且hash值为MOVED，说明该链表正在进行transfer操作，返回扩容完成后的table。 else if ((fh = f.hash) == MOVED)
tab = helpTransfer(tab, f); else {
V oldVal = null;
// 针对首个节点进行加锁操作，而不是segment，进一步减少线程冲突
synchronized (f) {
if (tabAt(tab, i) == f) {
if (fh >= 0) {
binCount = 1;
for (Node e = f;; ++binCount) {
K ek;
// 如果在链表中找到值为key的节点e，直接设置e.val = value即可。
if (e.hash == hash && ((ek = e.key) == key || (ek != null && key.equals(ek)))) {
oldVal = e.val;
if (!onlyIfAbsent)
e.val = value;
break;
}
// 如果没有找到值为key的节点，直接新建Node并加入链表即可。
Node pred = e;
if ((e = e.next) == null) {
pred.next = new Node(hash, key,
value, null);
break;
}
}
}
// 如果首节点为TreeBin类型，说明为红黑树结构，执行putTreeVal操作。 else if (f instanceof TreeBin) {
Node p;
binCount = 2;
if ((p = ((TreeBin)f).putTreeVal(hash, key,
value)) != null) {
oldVal = p.val;
if (!onlyIfAbsent)
p.val = value;
}
}
}
}
if (binCount != 0) {
// 如果节点数>＝8，那么转换链表结构为红黑树结构。
if (binCount >= TREEIFY_THRESHOLD)
treeifyBin(tab, i);
if (oldVal != null) return oldVal;
break;
}
}
}
// 计数增加1，有可能触发transfer操作(扩容)。
addCount(1L, binCount);
return null;
}

public class ConcurrentHashMapDemo { public static void main(String[] args) throws InterruptedException { // HashMap 在并发迭代访问时会抛出 ConcurrentModificationException 异常 // Map map = new HashMap<>();
Map map = new ConcurrentHashMap<>();
Thread wthread = new Thread(() -> {
System.out.println("写操作线程开始执行"); for (int i = 0; i <26; i++) {
map.put(i, (char) ('a' + i));
}
});
Thread rthread = new Thread(() -> {
System.out.println("读操作线程开始执行"); for (Integer key : map.keySet()) {
System.out.println(key + " - " + map.get(key));
}
});
wthread.start();
rthread.start();
Thread.sleep(1000);
}
}

 
/** The lock protecting all mutators */
final transient ReentrantLock lock = new ReentrantLock();
/** The array, accessed only via getArray/setArray. */
private transient volatile Object[] array;

public Boolean add(E e) {
//ReentrantLock加锁，保证线程安全
final ReentrantLock lock = this.lock;
lock.lock();
try {
Object[] elements = getArray();
int len = elements.length;
//拷贝原容器，长度为原容器长度加一
Object[] newElements = Arrays.copyOf(elements, len + 1);
//在新副本上执行添加操作
newElements[len] = e;
//将原容器引用指向新副本
setArray(newElements);
return true;
}
finally {
//解锁
lock.unlock();
}
}

public E remove(int index) {
//加锁
final ReentrantLock lock = this.lock;
lock.lock();
try {
Object[] elements = getArray();
int len = elements.length;
E oldValue = get(elements, index);
int numMoved = len - index - 1;
if (numMoved == 0) //如果要删除的是列表末端数据，拷贝前len-1个数据到新副本上，再切换引用
setArray(Arrays.copyOf(elements, len - 1)); else {
//否则，将除要删除元素之外的其他元素拷贝到新副本中，并切换引用
Object[] newElements = new Object[len - 1];
System.arraycopy(elements, 0, newElements, 0, index);
System.arraycopy(elements, index + 1, newElements, index,
numMoved);
setArray(newElements);
}
return oldValue;
}
finally {
//解锁
lock.unlock();
}
}

public E get(int index) {
return get(getArray(), index);
}
private E get(Object[] a, int index) {
return (E) a[index];
}

public class CopyOnWriteArrayListDemo { static class ReadTask implements Runnable {
List list;
ReadTask(List list) {
this.list = list;
}
public void run() {
for (String str : list) {
System.out.println(str);
}
}
}
static class WriteTask implements Runnable {
List list;
int index;
WriteTask(List list, int index) {
this.list = list;
this.index = index;
}
public void run() {
list.remove(index);
list.add(index, "write_" + index);
}
}
public void run() {
final int NUM = 10;
// ArrayList 在并发迭代访问时会抛出 ConcurrentModificationException 异常 // List list = new ArrayList<>();
CopyOnWriteArrayList list = new CopyOnWriteArrayList<>();
for (int i = 0; i