JAVA编程思想笔记:并发[三]

性能调优

lock 和  synchronized

//: concurrency/SynchronizationComparisons.java
package concurrency; /* Added by Eclipse.py */
// Comparing the performance of explicit Locks
// and Atomics versus the synchronized keyword.
import java.util.concurrent.*;
import java.util.concurrent.atomic.*;
import java.util.concurrent.locks.*;
import java.util.*;
import static net.mindview.util.Print.*;abstract class Accumulator {public static long cycles &＃61; 50000L;// Number of Modifiers and Readers during each test:private static final int N &＃61; 4;public static ExecutorService exec &＃61;Executors.newFixedThreadPool(N*2);private static CyclicBarrier barrier &＃61;new CyclicBarrier(N*2 &＃43; 1);protected volatile int index &＃61; 0;protected volatile long value &＃61; 0;protected long duration &＃61; 0;protected String id &＃61; "error";protected final static int SIZE &＃61; 100000;protected static int[] preLoaded &＃61; new int[SIZE];static {// Load the array of random numbers:Random rand &＃61; new Random(47);for(int i &＃61; 0; i }class BaseLine extends Accumulator {{ id &＃61; "BaseLine"; }public void accumulate() {if( index &＃61; SIZE) index &＃61; 0;}}public long read() { return value; }
}class SynchronizedTest extends Accumulator {{ id &＃61; "synchronized"; }public synchronized void accumulate() {value &＃43;&＃61; preLoaded[index&＃43;&＃43;];if(index >&＃61; SIZE) index &＃61; 0;}public synchronized long read() {return value;}
}class LockTest extends Accumulator {{ id &＃61; "Lock"; }private Lock lock &＃61; new ReentrantLock();public void accumulate() {lock.lock();try {value &＃43;&＃61; preLoaded[index&＃43;&＃43;];if(index >&＃61; SIZE) index &＃61; 0;} finally {lock.unlock();}}public long read() {lock.lock();try {return value;} finally {lock.unlock();}}
}class AtomicTest extends Accumulator {{ id &＃61; "Atomic"; }private AtomicInteger index &＃61; new AtomicInteger(0);private AtomicLong value &＃61; new AtomicLong(0);public void accumulate() {// Oops! Relying on more than one Atomic at// a time doesn&＃39;t work. But it still gives us// a performance indicator:int i &＃61; index.getAndIncrement();if( index.get() &＃61; SIZE)index.set(0);}}public long read() { return value.get(); }
}public class SynchronizationComparisons {static BaseLine baseLine &＃61; new BaseLine();static SynchronizedTest synch &＃61; new SynchronizedTest();static LockTest lock &＃61; new LockTest();static AtomicTest atomic &＃61; new AtomicTest();static void test() {print("&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;");printf("%-12s : %13d\n", "Cycles", Accumulator.cycles);baseLine.timedTest();synch.timedTest();lock.timedTest();atomic.timedTest();Accumulator.report(synch, baseLine);Accumulator.report(lock, baseLine);Accumulator.report(atomic, baseLine);Accumulator.report(synch, lock);Accumulator.report(synch, atomic);Accumulator.report(lock, atomic);}public static void main(String[] args) {int iterations &＃61; 5; // Defaultif(args.length > 0) // Optionally change iterationsiterations &＃61; new Integer(args[0]);// The first time fills the thread pool:print("Warmup");baseLine.timedTest();// Now the initial test doesn&＃39;t include the cost// of starting the threads for the first time.// Produce multiple data points:for(int i &＃61; 0; i }

输出结果:

Connected to the target VM, address: &＃39;127.0.0.1:62371&＃39;, transport: &＃39;socket&＃39;
Warmup
BaseLine : 21694209
&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;
Cycles : 50000
BaseLine : 2180204
synchronized : 42437398
Lock : 30372376
Atomic : 26275467
synchronized/BaseLine : 19.46
Lock/BaseLine : 13.93
Atomic/BaseLine : 12.05
synchronized/Lock : 1.40
synchronized/Atomic : 1.62
Lock/Atomic : 1.16
&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;
Cycles : 100000
BaseLine : 5193179
synchronized : 82977464
Lock : 31370928
Atomic : 11210371
synchronized/BaseLine : 15.98
Lock/BaseLine : 6.04
Atomic/BaseLine : 2.16
synchronized/Lock : 2.65
synchronized/Atomic : 7.40
Lock/Atomic : 2.80
&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;
Cycles : 200000
BaseLine : 8938838
synchronized : 165124963
Lock : 78268801
Atomic : 13180858
synchronized/BaseLine : 18.47
Lock/BaseLine : 8.76
Atomic/BaseLine : 1.47
synchronized/Lock : 2.11
synchronized/Atomic : 12.53
Lock/Atomic : 5.94
&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;
Cycles : 400000
BaseLine : 24426392
synchronized : 331777960
Lock : 115546684
Atomic : 29905100
synchronized/BaseLine : 13.58
Lock/BaseLine : 4.73
Atomic/BaseLine : 1.22
synchronized/Lock : 2.87
synchronized/Atomic : 11.09
Lock/Atomic : 3.86
&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;
Cycles : 800000
BaseLine : 34345855
synchronized : 633854425
Lock : 245733266
Atomic : 87583065
synchronized/BaseLine : 18.46
Lock/BaseLine : 7.15
Atomic/BaseLine : 2.55
synchronized/Lock : 2.58
synchronized/Atomic : 7.24
Lock/Atomic : 2.81
&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;
Cycles : 1600000
BaseLine : 62631708
synchronized : 1594457825
Lock : 654792500
Atomic : 138332107
synchronized/BaseLine : 25.46
Lock/BaseLine : 10.45
Atomic/BaseLine : 2.21
synchronized/Lock : 2.44
synchronized/Atomic : 11.53
Lock/Atomic : 4.73
&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;
Cycles : 3200000
BaseLine : 128165186
synchronized : 3528972948
Lock : 1278760479
Atomic : 285986269
synchronized/BaseLine : 27.53
Lock/BaseLine : 9.98
Atomic/BaseLine : 2.23
synchronized/Lock : 2.76
synchronized/Atomic : 12.34
Lock/Atomic : 4.47
&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;&＃61;
Cycles : 6400000
BaseLine : 220485251
synchronized : 6981991134
Lock : 2650398226
Atomic : 500422566
synchronized/BaseLine : 31.67
Lock/BaseLine : 12.02
Atomic/BaseLine : 2.27
synchronized/Lock : 2.63
synchronized/Atomic : 13.95
Lock/Atomic : 5.30

整理成表格:

使用 Lock 通常会比使用 synchronized 要高效

免锁容器

　CopyOnWriteArrayList是Java并发包中提供的一个并发容器&＃xff0c;它是个线程安全且读操作无锁的ArrayList&＃xff0c;写操作则通过创建底层数组的新副本来实现&＃xff0c;是一种读写分离的并发策略&＃xff0c;我们也可以称这种容器为"写时复制器"&＃xff0c;Java并发包中类似的容器还有CopyOnWriteSet。

优缺点分析

　　了解了CopyOnWriteArrayList的实现原理&＃xff0c;分析它的优缺点及使用场景就很容易了。

　　优点&＃xff1a;

　　读操作性能很高&＃xff0c;因为无需任何同步措施&＃xff0c;比较适用于读多写少的并发场景。Java的list在遍历时&＃xff0c;若中途有别的线程对list容器进行修改&＃xff0c;则会抛出ConcurrentModificationException异常。而CopyOnWriteArrayList由于其"读写分离"的思想&＃xff0c;遍历和修改操作分别作用在不同的list容器&＃xff0c;所以在使用迭代器进行遍历时候&＃xff0c;也就不会抛出ConcurrentModificationException异常了

　　缺点&＃xff1a;

　　缺点也很明显&＃xff0c;一是内存占用问题&＃xff0c;毕竟每次执行写操作都要将原容器拷贝一份&＃xff0c;数据量大时&＃xff0c;对内存压力较大&＃xff0c;可能会引起频繁GC&＃xff1b;二是无法保证实时性&＃xff0c;Vector对于读写操作均加锁同步&＃xff0c;可以保证读和写的强一致性。而CopyOnWriteArrayList由于其实现策略的原因&＃xff0c;写和读分别作用在新老不同容器上&＃xff0c;在写操作执行过程中&＃xff0c;读不会阻塞但读取到的却是老容器的数据。

CopyOnWriteArraySet 将使用CopyOnWriteArrayList来实现其免锁行为

ConcurrentHashMap和 ConcurrentLinkedQueue 使用了类似的技术,允许并发的读取和写入.但是容器中只有部分内容而不是整个容器可以被复制和修改.

ConcurrentHashMap不会抛出 ConcurrentModificationException.

乐观锁


Type Read time Write time
Synched ArrayList 10r 0w 3975043910 0
Synched ArrayList 10r 0w 2766145687 0
Synched ArrayList 10r 0w 2324410921 0
Synched ArrayList 10r 0w 2352972749 0
Synched ArrayList 10r 0w 2511789031 0
Synched ArrayList 10r 0w 2987712606 0
Synched ArrayList 10r 0w 2602829236 0
Synched ArrayList 10r 0w 3502788085 0
Synched ArrayList 10r 0w 4335015877 0
Synched ArrayList 10r 0w 4047738828 0CopyOnWriteArrayList 10r 0w 127857882 0
CopyOnWriteArrayList 10r 0w 62679837 0
CopyOnWriteArrayList 10r 0w 54443863 0
CopyOnWriteArrayList 10r 0w 56359211 0
CopyOnWriteArrayList 10r 0w 74350707 0
CopyOnWriteArrayList 10r 0w 62574412 0
CopyOnWriteArrayList 10r 0w 60151492 0
CopyOnWriteArrayList 10r 0w 68195080 0
CopyOnWriteArrayList 10r 0w 74290655 0
CopyOnWriteArrayList 10r 0w 62879388 0预计相差 40 倍Synched ArrayList 9r 1w 4351248439 519078520
readTime &＃43; writeTime &＃61; 4870326959
Synched ArrayList 9r 1w 4580132832 528211025
readTime &＃43; writeTime &＃61; 5108343857
Synched ArrayList 9r 1w 4535477318 530243150
readTime &＃43; writeTime &＃61; 5065720468
Synched ArrayList 9r 1w 3729192259 449021236
readTime &＃43; writeTime &＃61; 4178213495
Synched ArrayList 9r 1w 4310570520 516373800
readTime &＃43; writeTime &＃61; 4826944320
Synched ArrayList 9r 1w 3727406116 444126621
readTime &＃43; writeTime &＃61; 4171532737
Synched ArrayList 9r 1w 5088467838 581730237
readTime &＃43; writeTime &＃61; 5670198075
Synched ArrayList 9r 1w 3871264858 467694613
readTime &＃43; writeTime &＃61; 4338959471
Synched ArrayList 9r 1w 3907490866 475651205
readTime &＃43; writeTime &＃61; 4383142071
Synched ArrayList 9r 1w 4857326451 572377421
readTime &＃43; writeTime &＃61; 5429703872CopyOnWriteArrayList 9r 1w 64259585 58038121
readTime &＃43; writeTime &＃61; 122297706
CopyOnWriteArrayList 9r 1w 103041865 55306617
readTime &＃43; writeTime &＃61; 158348482
CopyOnWriteArrayList 9r 1w 76859340 45666997
readTime &＃43; writeTime &＃61; 122526337
CopyOnWriteArrayList 9r 1w 82963384 49150571
readTime &＃43; writeTime &＃61; 132113955
CopyOnWriteArrayList 9r 1w 85530058 47494007
readTime &＃43; writeTime &＃61; 133024065
CopyOnWriteArrayList 9r 1w 156166751 61169655
readTime &＃43; writeTime &＃61; 217336406
CopyOnWriteArrayList 9r 1w 102234854 50495800
readTime &＃43; writeTime &＃61; 152730654
CopyOnWriteArrayList 9r 1w 118083485 59992123
readTime &＃43; writeTime &＃61; 178075608
CopyOnWriteArrayList 9r 1w 168668483 60294659
readTime &＃43; writeTime &＃61; 228963142
CopyOnWriteArrayList 9r 1w 83152493 52633779
readTime &＃43; writeTime &＃61; 135786272预计相差 30 倍Synched ArrayList 5r 5w 1859681520 3059611972
readTime &＃43; writeTime &＃61; 4919293492
Synched ArrayList 5r 5w 2339497789 3231858118
readTime &＃43; writeTime &＃61; 5571355907
Synched ArrayList 5r 5w 1759631869 2999467850
readTime &＃43; writeTime &＃61; 4759099719
Synched ArrayList 5r 5w 1872095383 3013864853
readTime &＃43; writeTime &＃61; 4885960236
Synched ArrayList 5r 5w 2991087849 3226872592
readTime &＃43; writeTime &＃61; 6217960441
Synched ArrayList 5r 5w 2434089947 3523933235
readTime &＃43; writeTime &＃61; 5958023182
Synched ArrayList 5r 5w 2536545986 3119941132
readTime &＃43; writeTime &＃61; 5656487118
Synched ArrayList 5r 5w 2571197431 3003374484
readTime &＃43; writeTime &＃61; 5574571915
Synched ArrayList 5r 5w 2222675410 2791449002
readTime &＃43; writeTime &＃61; 5014124412
Synched ArrayList 5r 5w 1583914850 2689629756
readTime &＃43; writeTime &＃61; 4273544606CopyOnWriteArrayList 5r 5w 142259670 1206935112
readTime &＃43; writeTime &＃61; 1349194782
CopyOnWriteArrayList 5r 5w 49615047 995217184
readTime &＃43; writeTime &＃61; 1044832231
CopyOnWriteArrayList 5r 5w 31987043 977226939
readTime &＃43; writeTime &＃61; 1009213982
CopyOnWriteArrayList 5r 5w 66506805 1040415224
readTime &＃43; writeTime &＃61; 1106922029
CopyOnWriteArrayList 5r 5w 35032835 994549959
readTime &＃43; writeTime &＃61; 1029582794
CopyOnWriteArrayList 5r 5w 38461110 1002445848
readTime &＃43; writeTime &＃61; 1040906958
CopyOnWriteArrayList 5r 5w 50651685 1071667187
readTime &＃43; writeTime &＃61; 1122318872
CopyOnWriteArrayList 5r 5w 32006848 1001262532
readTime &＃43; writeTime &＃61; 1033269380
CopyOnWriteArrayList 5r 5w 36295220 1011740649
readTime &＃43; writeTime &＃61; 1048035869
CopyOnWriteArrayList 5r 5w 34283434 1050960270
readTime &＃43; writeTime &＃61; 1085243704预计相差 4 倍

CopyOnWriteArrayList性能 要比 SynchronizedArrayList 性能好一些. 当读的情况多的时候,会有几十倍的差距.

当读写数据量大小趋向于平均时, 性能还有将近四倍的差距.

比较各种 Map 实现

Type Read time Write time
Synched HashMap 10r 0w 6242418056 0
Synched HashMap 10r 0w 4146402296 0
Synched HashMap 10r 0w 5575418578 0
Synched HashMap 10r 0w 3834073584 0
Synched HashMap 10r 0w 5194782005 0
Synched HashMap 10r 0w 5161536963 0
Synched HashMap 10r 0w 4444520893 0
Synched HashMap 10r 0w 3871868695 0
Synched HashMap 10r 0w 4408989207 0
Synched HashMap 10r 0w 8023118598 0ConcurrentHashMap 10r 0w 344685546 0
ConcurrentHashMap 10r 0w 346848415 0
ConcurrentHashMap 10r 0w 318704071 0
ConcurrentHashMap 10r 0w 405478178 0
ConcurrentHashMap 10r 0w 207930162 0
ConcurrentHashMap 10r 0w 366067455 0
ConcurrentHashMap 10r 0w 226500276 0
ConcurrentHashMap 10r 0w 296423990 0
ConcurrentHashMap 10r 0w 320249183 0
ConcurrentHashMap 10r 0w 508154405 0读取性能差 10 倍以上Synched HashMap 9r 1w 6513091741 753915689
readTime &＃43; writeTime &＃61; 7267007430
Synched HashMap 9r 1w 6028976406 641421250
readTime &＃43; writeTime &＃61; 6670397656
Synched HashMap 9r 1w 5676651670 653679779
readTime &＃43; writeTime &＃61; 6330331449
Synched HashMap 9r 1w 5908498114 494457577
readTime &＃43; writeTime &＃61; 6402955691
Synched HashMap 9r 1w 7834818531 844974551
readTime &＃43; writeTime &＃61; 8679793082
Synched HashMap 9r 1w 5914246757 645557937
readTime &＃43; writeTime &＃61; 6559804694
Synched HashMap 9r 1w 7138638960 744661626
readTime &＃43; writeTime &＃61; 7883300586
Synched HashMap 9r 1w 6789718783 710857815
readTime &＃43; writeTime &＃61; 7500576598
Synched HashMap 9r 1w 5310600463 599121405
readTime &＃43; writeTime &＃61; 5909721868
Synched HashMap 9r 1w 5655007305 586903118
readTime &＃43; writeTime &＃61; 6241910423ConcurrentHashMap 9r 1w 216104674 54419560
readTime &＃43; writeTime &＃61; 270524234
ConcurrentHashMap 9r 1w 294262252 40927173
readTime &＃43; writeTime &＃61; 335189425
ConcurrentHashMap 9r 1w 264142918 43273241
readTime &＃43; writeTime &＃61; 307416159
ConcurrentHashMap 9r 1w 273924527 48728635
readTime &＃43; writeTime &＃61; 322653162
ConcurrentHashMap 9r 1w 369514606 50730634
readTime &＃43; writeTime &＃61; 420245240
ConcurrentHashMap 9r 1w 219419103 38947284
readTime &＃43; writeTime &＃61; 258366387
ConcurrentHashMap 9r 1w 252190432 30225329
readTime &＃43; writeTime &＃61; 282415761
ConcurrentHashMap 9r 1w 228296180 25051090
readTime &＃43; writeTime &＃61; 253347270
ConcurrentHashMap 9r 1w 303395962 49612912
readTime &＃43; writeTime &＃61; 353008874
ConcurrentHashMap 9r 1w 171637818 35856054
readTime &＃43; writeTime &＃61; 207493872预计相差 25 倍以上.Synched HashMap 5r 5w 3787200263 3601518353
readTime &＃43; writeTime &＃61; 7388718616
Synched HashMap 5r 5w 3089274985 2733346333
readTime &＃43; writeTime &＃61; 5822621318
Synched HashMap 5r 5w 3408395059 3113962082
readTime &＃43; writeTime &＃61; 6522357141
Synched HashMap 5r 5w 3981206639 3679965007
readTime &＃43; writeTime &＃61; 7661171646
Synched HashMap 5r 5w 3265915194 3142623898
readTime &＃43; writeTime &＃61; 6408539092
Synched HashMap 5r 5w 3164752807 3000101498
readTime &＃43; writeTime &＃61; 6164854305
Synched HashMap 5r 5w 3336219924 3014104874
readTime &＃43; writeTime &＃61; 6350324798
Synched HashMap 5r 5w 3124944592 2991122381
readTime &＃43; writeTime &＃61; 6116066973
Synched HashMap 5r 5w 3977208930 3839928054
readTime &＃43; writeTime &＃61; 7817136984
Synched HashMap 5r 5w 3074772608 2874037633
readTime &＃43; writeTime &＃61; 5948810241ConcurrentHashMap 5r 5w 99540221 462089771
readTime &＃43; writeTime &＃61; 561629992
ConcurrentHashMap 5r 5w 240567089 518136870
readTime &＃43; writeTime &＃61; 758703959
ConcurrentHashMap 5r 5w 155490877 432835809
readTime &＃43; writeTime &＃61; 588326686
ConcurrentHashMap 5r 5w 220516994 483831256
readTime &＃43; writeTime &＃61; 704348250
ConcurrentHashMap 5r 5w 216032229 572084619
readTime &＃43; writeTime &＃61; 788116848
ConcurrentHashMap 5r 5w 197179986 620970499
readTime &＃43; writeTime &＃61; 818150485
ConcurrentHashMap 5r 5w 254407618 544484450
readTime &＃43; writeTime &＃61; 798892068
ConcurrentHashMap 5r 5w 208138769 501331795
readTime &＃43; writeTime &＃61; 709470564
ConcurrentHashMap 5r 5w 180873142 492012085
readTime &＃43; writeTime &＃61; 672885227
ConcurrentHashMap 5r 5w 164806795 559711679
readTime &＃43; writeTime &＃61; 724518474预计相差 10 倍以上

ConcurrentHashMap 完虐  synchronizedMap

乐观加锁

//: concurrency/FastSimulation.java
package concurrency; /* Added by Eclipse.py */
import java.util.concurrent.*;
import java.util.concurrent.atomic.*;
import java.util.*;
import static net.mindview.util.Print.*;public class FastSimulation {static final int N_ELEMENTS &＃61; 100000;static final int N_GENES &＃61; 30;static final int N_EVOLVERS &＃61; 50;static final AtomicInteger[][] GRID &＃61;new AtomicInteger[N_ELEMENTS][N_GENES];static Random rand &＃61; new Random(47);static class Evolver implements Runnable {public void run() {while(!Thread.interrupted()) {// Randomly select an element to work on:int element &＃61; rand.nextInt(N_ELEMENTS);for(int i &＃61; 0; i &＃61; N_ELEMENTS) next &＃61; 0;int oldvalue &＃61; GRID[element][i].get();// Perform some kind of modeling calculation:int newvalue &＃61; oldvalue &＃43;GRID[previous][i].get() &＃43; GRID[next][i].get();newvalue /&＃61; 3; // Average the three valuesif(!GRID[element][i].compareAndSet(oldvalue, newvalue)) {// Policy here to deal with failure. Here, we// just report it and ignore it; our model// will eventually deal with it.print("Old value changed from " &＃43; oldvalue);}}}}}public static void main(String[] args) throws Exception {ExecutorService exec &＃61; Executors.newCachedThreadPool();for(int i &＃61; 0; i } /* (Execute to see output) *///:~


ReadWriteLock

//: concurrency/ReaderWriterList.java
package concurrency; /* Added by Eclipse.py */
import java.util.concurrent.*;
import java.util.concurrent.locks.*;
import java.util.*;
import static net.mindview.util.Print.*;public class ReaderWriterList {private ArrayList lockedList;// Make the ordering fair:private ReentrantReadWriteLock lock &＃61;new ReentrantReadWriteLock(true);public ReaderWriterList(int size, T initialValue) {lockedList &＃61; new ArrayList(Collections.nCopies(size, initialValue));}public T set(int index, T element) {Lock wlock &＃61; lock.writeLock();wlock.lock();try {return lockedList.set(index, element);} finally {wlock.unlock();}}public T get(int index) {Lock rlock &＃61; lock.readLock();rlock.lock();try {// Show that multiple readers// may acquire the read lock:if(lock.getReadLockCount() > 1)print(lock.getReadLockCount());return lockedList.get(index);} finally {rlock.unlock();}}public static void main(String[] args) throws Exception {new ReaderWriterListTest(30, 1);}
}class ReaderWriterListTest {ExecutorService exec &＃61; Executors.newCachedThreadPool();private final static int SIZE &＃61; 100;private static Random rand &＃61; new Random(47);private ReaderWriterList list &＃61;new ReaderWriterList(SIZE, 0);private class Writer implements Runnable {public void run() {try {for(int i &＃61; 0; i <20; i&＃43;&＃43;) { // 2 second testlist.set(i, rand.nextInt());TimeUnit.MILLISECONDS.sleep(100);}} catch(InterruptedException e) {// Acceptable way to exit}print("Writer finished, shutting down");exec.shutdownNow();}}private class Reader implements Runnable {public void run() {try {while(!Thread.interrupted()) {for(int i &＃61; 0; i } /* (Execute to see output) *///:~