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/*
* Copyright (c) 2010, Code Aurora Forum. All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions are met:
* * Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* * Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
* * Neither the name of Code Aurora nor
* the names of its contributors may be used to endorse or promote
* products derived from this software without specific prior written
* permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
* AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
* NON-INFRINGEMENT ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR
* CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
* EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
* PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS;
* OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
* WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR
* OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
* ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/
package android.webkit;
import android.os.Handler;
import android.util.Log;
import android.os.Message;
import android.os.Process;
import java.lang.Thread;
import java.lang.InterruptedException;
import java.net.UnknownHostException;
import java.util.concurrent.Executors;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Semaphore;
import java.util.HashMap;
import java.util.Iterator;
import java.util.Map;
final class DnsResolver {
private static final String LOGTAG = "webcore";
/* Max Thread pool size is taken from data published by google
* that mentions max hosts per webpage = 8 */
private final int MAX_DNS_RESOLVER_THREAD_POOL_SIZE = 8;
/* This number is derived by considering various factors such as OS DNS cache size,
* Browser Cache size and realistic need to spent time on DNS prefetch
*/
private final int MAX_PARALLEL_DNS_QUERIES_PER_PAGE = 64;
private volatile boolean mDnsResolverThreadPoolRunning = false;
private volatile boolean mShutDownInProgress = false;
private static DnsResolver sDnsResolver;
private HashMap mHostNamesToBeResolved;
private ExecutorService mDnsResolverThreadPool;
private static int mDnsResolverRefCount = 0;
/* Lock to synchronize the access to threadpool */
private static Object mThreadPoolLock = new Object();
public static synchronized DnsResolver createDnsResolver() {
if (DebugFlags.WEB_VIEW_CORE)
Log.v(LOGTAG, "Creating DNS resolver");
if (sDnsResolver == null) {
sDnsResolver = new DnsResolver();
}
++mDnsResolverRefCount;
return sDnsResolver;
}
public static DnsResolver getInstance() {
return sDnsResolver;
}
private DnsResolver() {
mHostNamesToBeResolved = new HashMap();
createDnsResolverThreadPool();
}
private void createDnsResolverThreadPool() {
final Runnable startDnsResolver = new Runnable() {
public void run() {
/* DNS resolver priority should be same as of HTTP thread pool */
Process.setThreadPriority( android.os.Process.THREAD_PRIORITY_DEFAULT +
android.os.Process.THREAD_PRIORITY_LESS_FAVORABLE);
mDnsResolverThreadPool = Executors.newFixedThreadPool(MAX_DNS_RESOLVER_THREAD_POOL_SIZE);
boolean bResolvedPriorityHostNames = false;
int dnsQueryCounter = 0;
int numHosts = 0;
while(!mShutDownInProgress) {
synchronized(mHostNamesToBeResolved) {
numHosts = mHostNamesToBeResolved.size();
}
if(numHosts <= 0) {
try {
dnsQueryCounter = 0;
bResolvedPriorityHostNames = false;
mDnsResolverThreadPoolRunning = true;
synchronized(mThreadPoolLock) {
mThreadPoolLock.wait();
}
} catch(java.lang.InterruptedException e) {
}
}
else {
synchronized(mHostNamesToBeResolved) {
Iterator iterator = mHostNamesToBeResolved.entrySet().iterator();
while(iterator.hasNext() && mDnsResolverThreadPoolRunning && (dnsQueryCounter < MAX_PARALLEL_DNS_QUERIES_PER_PAGE)) {
Map.Entry entry = (Map.Entry) iterator.next();
final String hostName = (String)entry.getKey();
final String priority = (String)entry.getValue();
if( (!bResolvedPriorityHostNames && priority.equalsIgnoreCase("1")) ||
( bResolvedPriorityHostNames && priority.equalsIgnoreCase("0"))
) {
++dnsQueryCounter;
iterator.remove();
Runnable task = new Runnable() {
public void run() {
try {
java.net.InetAddress.getByName(hostName);
} catch(java.net.UnknownHostException e) {
}
}
};
mDnsResolverThreadPool.execute (task);
}
}
if(!mDnsResolverThreadPoolRunning || (dnsQueryCounter >= MAX_PARALLEL_DNS_QUERIES_PER_PAGE)) {
mHostNamesToBeResolved.clear();
}
bResolvedPriorityHostNames = (bResolvedPriorityHostNames) ? false:true;
}
}
}
mDnsResolverThreadPool.shutdown();
sDnsResolver = null;
}
};
Thread dnsResolver = new Thread(startDnsResolver);
dnsResolver.setName("DNS resolver");
dnsResolver.start();
}
public synchronized void destroyDnsResolver() {
if (DebugFlags.WEB_VIEW_CORE)
Log.v(LOGTAG, "Destroying DNS Resolver");
--mDnsResolverRefCount;
if(mDnsResolverRefCount == 0) {
mShutDownInProgress = true;
mDnsResolverThreadPoolRunning = false;
synchronized(mThreadPoolLock) {
mThreadPoolLock.notifyAll();
}
}
}
public void resolveDnsForHost(String hostName, String priority) {
if(hostName == null) {
return;
}
synchronized(mHostNamesToBeResolved) {
if(mHostNamesToBeResolved.size() > 0 ) {
return;
}
mHostNamesToBeResolved.put(hostName,priority);
}
resumeDnsResolverThreadPool();
}
public void resolveDnsForHostMap(HashMap hostMap) {
if(hostMap == null) {
return;
}
synchronized (mHostNamesToBeResolved) {
mHostNamesToBeResolved.putAll(hostMap);
}
resumeDnsResolverThreadPool();
}
/* pause will flush all pending DNS queries at the DNS resolver */
public void pauseDnsResolverThreadPool() {
mDnsResolverThreadPoolRunning = false;
}
/* resume will start DNS resolver executing DNS queries */
public void resumeDnsResolverThreadPool() {
mDnsResolverThreadPoolRunning = true;
synchronized(mThreadPoolLock) {
mThreadPoolLock.notifyAll();
}
}
/* returns the max number of DNS queries that can be made in background for a page */
public int getMaxParallelDnsQueryPerPage() {
return MAX_PARALLEL_DNS_QUERIES_PER_PAGE;
}
}
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