1/* 2 * Copyright (C) 2009 Apple Inc. All Rights Reserved. 3 * Copyright (C) 2012 Igalia S.L. 4 * 5 * Redistribution and use in source and binary forms, with or without 6 * modification, are permitted provided that the following conditions 7 * are met: 8 * 1. Redistributions of source code must retain the above copyright 9 * notice, this list of conditions and the following disclaimer. 10 * 2. Redistributions in binary form must reproduce the above copyright 11 * notice, this list of conditions and the following disclaimer in the 12 * documentation and/or other materials provided with the distribution. 13 * 14 * THIS SOFTWARE IS PROVIDED BY APPLE AND ITS CONTRIBUTORS "AS IS" AND ANY 15 * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 16 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR 17 * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL APPLE COMPUTER, INC. OR 18 * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, 19 * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, 20 * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR 21 * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY 22 * OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT 23 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE 24 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 25 */ 26 27#include "config.h" 28#include "DNSResolveQueue.h" 29 30#include <wtf/CurrentTime.h> 31 32namespace WebCore { 33 34// When resolve queue is empty, we fire async resolution requests immediately (which is important if the prefetch is triggered by hovering). 35// But during page parsing, we should coalesce identical requests to avoid stressing out the DNS resolver. 36static const int gNamesToResolveImmediately = 4; 37 38// Coalesce prefetch requests for this long before sending them out. 39static const double gCoalesceDelayInSeconds = 1.0; 40 41// Sending many DNS requests at once can overwhelm some gateways. See <rdar://8105550> for specific CFNET issues with CFHost throttling. 42static const int gMaxSimultaneousRequests = 8; 43 44// For a page has links to many outside sites, it is likely that the system DNS resolver won't be able to cache them all anyway, and we don't want 45// to negatively affect other applications' performance by pushing their cached entries out. 46// If we end up with lots of names to prefetch, some will be dropped. 47static const int gMaxRequestsToQueue = 64; 48 49// If there were queued names that couldn't be sent simultaneously, check the state of resolvers after this delay. 50static const double gRetryResolvingInSeconds = 0.1; 51 52DNSResolveQueue::DNSResolveQueue() 53 : m_requestsInFlight(0) 54 , m_cachedProxyEnabledStatus(false) 55 , m_lastProxyEnabledStatusCheckTime(0) 56{ 57} 58 59bool DNSResolveQueue::isUsingProxy() 60{ 61 double time = currentTime(); 62 static const double minimumProxyCheckDelay = 5; 63 if (time - m_lastProxyEnabledStatusCheckTime > minimumProxyCheckDelay) { 64 m_lastProxyEnabledStatusCheckTime = time; 65 m_cachedProxyEnabledStatus = platformProxyIsEnabledInSystemPreferences(); 66 } 67 return m_cachedProxyEnabledStatus; 68} 69 70void DNSResolveQueue::add(const String& hostname) 71{ 72 // If there are no names queued, and few enough are in flight, resolve immediately (the mouse may be over a link). 73 if (!m_names.size()) { 74 if (isUsingProxy()) 75 return; 76 if (atomicIncrement(&m_requestsInFlight) <= gNamesToResolveImmediately) { 77 platformResolve(hostname); 78 return; 79 } 80 atomicDecrement(&m_requestsInFlight); 81 } 82 83 // It's better to not prefetch some names than to clog the queue. 84 // Dropping the newest names, because on a single page, these are likely to be below oldest ones. 85 if (m_names.size() < gMaxRequestsToQueue) { 86 m_names.add(hostname); 87 if (!isActive()) 88 startOneShot(gCoalesceDelayInSeconds); 89 } 90} 91 92void DNSResolveQueue::fired() 93{ 94 if (isUsingProxy()) { 95 m_names.clear(); 96 return; 97 } 98 99 int requestsAllowed = gMaxSimultaneousRequests - m_requestsInFlight; 100 101 for (; !m_names.isEmpty() && requestsAllowed > 0; --requestsAllowed) { 102 atomicIncrement(&m_requestsInFlight); 103 HashSet<String>::iterator currentName = m_names.begin(); 104 platformResolve(*currentName); 105 m_names.remove(currentName); 106 } 107 108 if (!m_names.isEmpty()) 109 startOneShot(gRetryResolvingInSeconds); 110} 111 112} // namespace WebCore 113