Java 多线程编程之四：获取 Java VM 中当前运行的所有线程

获取 Java VM 中当前运行的所有线程

程序运行图：

下面的静态方法可以用数组返回 Java VM 中当前运行的所有线程
public static Thread[] findAllThreads() {
ThreadGroup group =
Thread.currentThread().getThreadGroup();
ThreadGroup topGroup = group;

// 遍历线程组树，获取根线程组
while ( group != null ) {
topGroup = group;
group = group.getParent();
}
// 激活的线程数加倍
int estimatedSize = topGroup.activeCount() * 2;
Thread[] slackList = new Thread[estimatedSize];
//获取根线程组的所有线程
int actualSize = topGroup.enumerate(slackList);
// copy into a list that is the exact size
Thread[] list = new Thread[actualSize];
System.arraycopy(slackList, 0, list, 0, actualSize);
return list;
}

程序 ThreadViewer.java 以图形方式显示 Java VM 中当前运行的所有线程,它每隔 2 秒自动刷新一次,以保持获得最新信息。程序 ThreadViewer.java 源代码：

packagethread;
importjava.awt.*;
importjava.awt.event.*;
importjavax.swing.*;
importjavax.swing.table.*;
publicclassThreadViewerextendsJPanel{
privateThreadViewerTableModeltableModel;
publicThreadViewer(){
tableModel=newThreadViewerTableModel();
JTabletable=newJTable(tableModel);
table.setAutoResizeMode(JTable.AUTO_RESIZE_LAST_COLUMN);
TableColumnModelcolModel=table.getColumnModel();
intnumColumns=colModel.getColumnCount();
//manuallysizeallbutthelastcolumn
for(inti=0;i<numColumns-1;i++){
TableColumncol=colModel.getColumn(i);
col.sizeWidthToFit();
col.setPreferredWidth(col.getWidth()+5);
col.setMaxWidth(col.getWidth()+5);
}
JScrollPanesp=newJScrollPane(table);
setLayout(newBorderLayout());
add(sp,BorderLayout.CENTER);
}
publicvoiddispose(){
tableModel.stopRequest();
}
protectedvoidfinalize()throwsThrowable{
dispose();
}
publicstaticJFramecreateFramedInstance(){
finalThreadViewerviewer=newThreadViewer();
finalJFramef=newJFrame("ThreadViewer");
f.addWindowListener(newWindowAdapter(){
publicvoidwindowClosing(WindowEvente){
f.setVisible(false);
f.dispose();
viewer.dispose();
}
});
f.setContentPane(viewer);
f.setSize(500,300);
f.setVisible(true);
returnf;
}

publicstaticvoidmain(String[]args){
JFramef=ThreadViewer.createFramedInstance();
//Forthisexample,exittheVMwhentheviewer
//frameisclosed.
f.addWindowListener(newWindowAdapter(){
publicvoidwindowClosing(WindowEvente){
System.exit(0);
}
});
//Keepthemainthreadfromexitingbyblocking
//onwait()foranotificationthatnevercomes.
Objectlock=newObject();
synchronized(lock){
try{
lock.wait();
}catch(InterruptedExceptionx){
}
}
}
}

程序 ThreadViewerTableModel.java 源代码：

packagethread;
importjava.awt.*;
importjava.lang.reflect.*;
importjavax.swing.*;
importjavax.swing.table.*;
publicclassThreadViewerTableModelextendsAbstractTableModel{
privateObjectdataLock;
privateintrowCount;
privateObject[][]cellData;
privateObject[][]pendingCellData;
//thecolumninformationremainsconstant
privatefinalintcolumnCount;
privatefinalString[]columnName;
privatefinalClass[]columnClass;
//self-runningobjectcontrolvariables
privateThreadinternalThread;
privatevolatilebooleannoStopRequested;
publicThreadViewerTableModel(){
rowCount=0;
cellData=newObject[0][0];
//JTableusesthisinformationforthecolumnheaders
String[]names={
"Priority","Alive",
"Daemon","Interrupted",
"ThreadGroup","ThreadName"};
columnName=names;

//JTableusesthisinformationforcellrendering
Class[]classes={
Integer.class,Boolean.class,
Boolean.class,Boolean.class,
String.class,String.class};
columnClass=classes;
columnCount=columnName.length;
//usedtocontrolconcurrentaccess
dataLock=newObject();
noStopRequested=true;
Runnabler=newRunnable(){
publicvoidrun(){
try{
runWork();
}catch(Exceptionx){
//incaseANYexceptionslipsthrough
x.printStackTrace();
}
}
};
internalThread=newThread(r,"ThreadViewer");
internalThread.setPriority(Thread.MAX_PRIORITY-2);
internalThread.setDaemon(true);
internalThread.start();
}
privatevoidrunWork(){
//Therun()methodoftransferPendingiscalledby
//theeventhandlingthreadforsafeconcurrency.
RunnabletransferPending=newRunnable(){
publicvoidrun(){
transferPendingCellData();
//MethodofAbstractTableModelthat
//causesthetabletobeupdated.
fireTableDataChanged();
}
};
while(noStopRequested){
try{
createPendingCellData();
SwingUtilities.invokeAndWait(transferPending);
Thread.sleep(2000);
}catch(InvocationTargetExceptiontx){
tx.printStackTrace();
stopRequest();
}catch(InterruptedExceptionx){
Thread.currentThread().interrupt();
}
}
}
publicvoidstopRequest(){
noStopRequested=false;
internalThread.interrupt();
}
publicbooleanisAlive(){
returninternalThread.isAlive();
}
privatevoidcreatePendingCellData(){
//thismethodiscalledbytheinternalthread
Thread[]thread=findAllThreads();
Object[][]cell=newObject[thread.length][columnCount];
for(inti=0;i<thread.length;i++){
Threadt=thread[i];
Object[]rowCell=cell[i];
rowCell[0]=newInteger(t.getPriority());
rowCell[1]=newBoolean(t.isAlive());
rowCell[2]=newBoolean(t.isDaemon());
rowCell[3]=newBoolean(t.isInterrupted());
rowCell[4]=t.getThreadGroup().getName();
rowCell[5]=t.getName();
}
synchronized(dataLock){
pendingCellData=cell;
}
}
privatevoidtransferPendingCellData(){
//thismethodiscalledbytheeventthread
synchronized(dataLock){
cellData=pendingCellData;
rowCount=cellData.length;
}
}
publicintgetRowCount(){
//thismethodiscalledbytheeventthread
returnrowCount;
}

publicObjectgetValueAt(introw,intcol){
//thismethodiscalledbytheeventthread
returncellData[row][col];
}
publicintgetColumnCount(){
returncolumnCount;
}
publicClassgetColumnClass(intcolumnIdx){
returncolumnClass[columnIdx];
}
publicStringgetColumnName(intcolumnIdx){
returncolumnName[columnIdx];
}
publicstaticThread[]findAllThreads(){
ThreadGroupgroup=
Thread.currentThread().getThreadGroup();
ThreadGrouptopGroup=group;
//traversetheThreadGrouptreetothetop
while(group!=null){
topGroup=group;
group=group.getParent();
}
//Createadestinationarraythatisabout
//twiceasbigasneededtobeveryconfident
//thatnoneareclipped.
intestimatedSize=topGroup.activeCount()*2;
Thread[]slackList=newThread[estimatedSize];
//Loadthethreadreferencesintotheoversized
//array.Theactualnumberofthreadsloaded
//isreturned.
intactualSize=topGroup.enumerate(slackList);
//copyintoalistthatistheexactsize
Thread[]list=newThread[actualSize];
System.arraycopy(slackList,0,list,0,actualSize);
returnlist;
}
}