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8293562: KeepAliveCache Blocks Threads while Closing Connections #402

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8293562: KeepAliveCache Blocks Threads while Closing Connections #402

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217 changes: 118 additions & 99 deletions jdk/src/share/classes/sun/net/www/http/KeepAliveCache.java
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Original file line number Diff line number Diff line change
Expand Up @@ -27,9 +27,11 @@

import java.io.IOException;
import java.io.NotSerializableException;
import java.util.ArrayDeque;
import java.util.ArrayList;
import java.util.HashMap;
import java.net.URL;
import java.util.List;

/**
* A class that implements a cache of idle Http connections for keep-alive
Expand Down Expand Up @@ -76,56 +78,68 @@ public KeepAliveCache() {}
* @param url The URL contains info about the host and port
* @param http The HttpClient to be cached
*/
public synchronized void put(final URL url, Object obj, HttpClient http) {
boolean startThread = (keepAliveTimer == null);
if (!startThread) {
if (!keepAliveTimer.isAlive()) {
startThread = true;
public void put(final URL url, Object obj, HttpClient http) {
// this method may need to close an HttpClient, either because
// it is not cacheable, or because the cache is at its capacity.
// In the latter case, we close the least recently used client.
// The client to close is stored in oldClient, and is closed
// after cacheLock is released.
HttpClient oldClient = null;
synchronized(this) {
boolean startThread = (keepAliveTimer == null);
if (!startThread) {
if (!keepAliveTimer.isAlive()) {
startThread = true;
}
}
}
if (startThread) {
clear();
/* Unfortunately, we can't always believe the keep-alive timeout we got
* back from the server. If I'm connected through a Netscape proxy
* to a server that sent me a keep-alive
* time of 15 sec, the proxy unilaterally terminates my connection
* The robustness to get around this is in HttpClient.parseHTTP()
*/
final KeepAliveCache cache = this;
java.security.AccessController.doPrivileged(
new java.security.PrivilegedAction<Void>() {
public Void run() {
// We want to create the Keep-Alive-Timer in the
// system threadgroup
ThreadGroup grp = Thread.currentThread().getThreadGroup();
ThreadGroup parent = null;
while ((parent = grp.getParent()) != null) {
grp = parent;
if (startThread) {
clear();
/* Unfortunately, we can't always believe the keep-alive timeout we got
* back from the server. If I'm connected through a Netscape proxy
* to a server that sent me a keep-alive
* time of 15 sec, the proxy unilaterally terminates my connection
* The robustness to get around this is in HttpClient.parseHTTP()
*/
final KeepAliveCache cache = this;
java.security.AccessController.doPrivileged(
new java.security.PrivilegedAction<Void>() {
public Void run() {
// We want to create the Keep-Alive-Timer in the
// system threadgroup
ThreadGroup grp = Thread.currentThread().getThreadGroup();
ThreadGroup parent = null;
while ((parent = grp.getParent()) != null) {
grp = parent;
}

keepAliveTimer = new Thread(grp, cache, "Keep-Alive-Timer");
keepAliveTimer.setDaemon(true);
keepAliveTimer.setPriority(Thread.MAX_PRIORITY - 2);
// Set the context class loader to null in order to avoid
// keeping a strong reference to an application classloader.
keepAliveTimer.setContextClassLoader(null);
keepAliveTimer.start();
return null;
}
});
}

keepAliveTimer = new Thread(grp, cache, "Keep-Alive-Timer");
keepAliveTimer.setDaemon(true);
keepAliveTimer.setPriority(Thread.MAX_PRIORITY - 2);
// Set the context class loader to null in order to avoid
// keeping a strong reference to an application classloader.
keepAliveTimer.setContextClassLoader(null);
keepAliveTimer.start();
return null;
}
});
KeepAliveKey key = new KeepAliveKey(url, obj);
ClientVector v = super.get(key);

if (v == null) {
int keepAliveTimeout = http.getKeepAliveTimeout();
v = new ClientVector(keepAliveTimeout > 0?
keepAliveTimeout*1000 : LIFETIME);
v.put(http);
super.put(key, v);
} else {
oldClient = v.put(http);
}
}

KeepAliveKey key = new KeepAliveKey(url, obj);
ClientVector v = super.get(key);

if (v == null) {
int keepAliveTimeout = http.getKeepAliveTimeout();
v = new ClientVector(keepAliveTimeout > 0?
keepAliveTimeout*1000 : LIFETIME);
v.put(http);
super.put(key, v);
} else {
v.put(http);
// close after releasing locks
if (oldClient != null) {
oldClient.closeServer();
}
}

Expand All @@ -135,7 +149,7 @@ public synchronized void remove (HttpClient h, Object obj) {
ClientVector v = super.get(key);
if (v != null) {
v.remove(h);
if (v.empty()) {
if (v.isEmpty()) {
removeVector(key);
}
}
Expand Down Expand Up @@ -171,39 +185,31 @@ public void run() {
try {
Thread.sleep(LIFETIME);
} catch (InterruptedException e) {}
synchronized (this) {
/* Remove all unused HttpClients. Starting from the
* bottom of the stack (the least-recently used first).
* REMIND: It'd be nice to not remove *all* connections
* that aren't presently in use. One could have been added
* a second ago that's still perfectly valid, and we're
* needlessly axing it. But it's not clear how to do this
* cleanly, and doing it right may be more trouble than it's
* worth.
*/
List<HttpClient> closeList = null;

// Remove all outdated HttpClients.
synchronized (this) {
long currentTime = System.currentTimeMillis();

ArrayList<KeepAliveKey> keysToRemove
= new ArrayList<KeepAliveKey>();
List<KeepAliveKey> keysToRemove = new ArrayList<>();

for (KeepAliveKey key : keySet()) {
ClientVector v = get(key);
synchronized (v) {
int i;

for (i = 0; i < v.size(); i++) {
KeepAliveEntry e = v.elementAt(i);
KeepAliveEntry e = v.peekLast();
while (e != null) {
if ((currentTime - e.idleStartTime) > v.nap) {
HttpClient h = e.hc;
h.closeServer();
v.pollLast();
if (closeList == null) {
closeList = new ArrayList<>();
}
closeList.add(e.hc);
} else {
break;
}
e = v.peekLast();
}
v.subList(0, i).clear();

if (v.size() == 0) {
if (v.isEmpty()) {
keysToRemove.add(key);
}
}
Expand All @@ -213,9 +219,13 @@ public void run() {
removeVector(key);
}
}
} while (size() > 0);

return;
// close connections outside cacheLock
if (closeList != null) {
for (HttpClient hc : closeList) {
hc.closeServer();
}
}
} while (!isEmpty());
}

/*
Expand All @@ -232,12 +242,10 @@ private void readObject(java.io.ObjectInputStream stream)
}
}

/* FILO order for recycling HttpClients, should run in a thread
* to time them out. If > maxConns are in use, block.
/* LIFO order for reusing HttpClients. Most recent entries at the front.
* If > maxConns are in use, discard oldest.
*/


class ClientVector extends java.util.Stack<KeepAliveEntry> {
class ClientVector extends ArrayDeque<KeepAliveEntry> {
private static final long serialVersionUID = -8680532108106489459L;

// sleep time in milliseconds, before cache clear
Expand All @@ -250,31 +258,42 @@ class ClientVector extends java.util.Stack<KeepAliveEntry> {
}

synchronized HttpClient get() {
if (empty()) {
// check the most recent connection, use if still valid
KeepAliveEntry e = peekFirst();
if (e == null) {
return null;
}

long currentTime = System.currentTimeMillis();
if ((currentTime - e.idleStartTime) > nap) {
return null; // all connections stale - will be cleaned up later
} else {
// Loop until we find a connection that has not timed out
HttpClient hc = null;
long currentTime = System.currentTimeMillis();
do {
KeepAliveEntry e = pop();
if ((currentTime - e.idleStartTime) > nap) {
e.hc.closeServer();
} else {
hc = e.hc;
}
} while ((hc== null) && (!empty()));
return hc;
pollFirst();
return e.hc;
}
}

/* remove an HttpClient */
synchronized boolean remove(HttpClient h) {
for (KeepAliveEntry curr : this) {
if (curr.hc == h) {
return super.remove(curr);
}
}
return false;
}

/* return a still valid, unused HttpClient */
synchronized void put(HttpClient h) {
synchronized HttpClient put(HttpClient h) {
HttpClient staleClient = null;
assert KeepAliveCache.getMaxConnections() > 0;
if (size() >= KeepAliveCache.getMaxConnections()) {
h.closeServer(); // otherwise the connection remains in limbo
} else {
push(new KeepAliveEntry(h, System.currentTimeMillis()));
// remove oldest connection
staleClient = removeLast().hc;
}
addFirst(new KeepAliveEntry(h, System.currentTimeMillis()));
// close after releasing the locks
return staleClient;
}

/*
Expand All @@ -293,10 +312,10 @@ private void readObject(java.io.ObjectInputStream stream)


class KeepAliveKey {
private String protocol = null;
private String host = null;
private int port = 0;
private Object obj = null; // additional key, such as socketfactory
private final String protocol;
private final String host;
private final int port;
private final Object obj; // additional key, such as socketfactory

/**
* Constructor
Expand Down Expand Up @@ -337,8 +356,8 @@ public int hashCode() {
}

class KeepAliveEntry {
HttpClient hc;
long idleStartTime;
final HttpClient hc;
final long idleStartTime;

KeepAliveEntry(HttpClient hc, long idleStartTime) {
this.hc = hc;
Expand Down
9 changes: 9 additions & 0 deletions jdk/src/share/classes/sun/net/www/protocol/https/HttpsClient.java
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Original file line number Diff line number Diff line change
Expand Up @@ -426,6 +426,15 @@ public boolean needsTunneling() {
&& proxy.type() != Proxy.Type.SOCKS);
}

@Override
public void closeServer() {
try {
// SSLSocket.close may block up to timeout. Make sure it's short.
serverSocket.setSoTimeout(1);
} catch (Exception e) {}
super.closeServer();
}

@Override
public void afterConnect() throws IOException, UnknownHostException {
if (!isCachedConnection()) {
Expand Down
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