net/proxy/multi_threaded_proxy_resolver.h

   1 // Copyright (c) 2011 The Chromium Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style license that can be
   3 // found in the LICENSE file.
   4
   5 #ifndef NET_PROXY_MULTI_THREADED_PROXY_RESOLVER_H_
   6 #define NET_PROXY_MULTI_THREADED_PROXY_RESOLVER_H_
   7
   8 #include <set>
   9
  10 #include "base/basictypes.h"
  11 #include "base/memory/ref_counted.h"
  12 #include "base/memory/scoped_ptr.h"
  13 #include "net/base/net_export.h"
  14 #include "net/proxy/proxy_resolver_factory.h"
  15
  16 namespace net {
  17 class ProxyResolver;
  18
  19 // MultiThreadedProxyResolverFactory creates instances of a ProxyResolver
  20 // implementation that runs synchronous ProxyResolver implementations on worker
  21 // threads.
  22 //
  23 // Threads are created lazily on demand, up to a maximum total. The advantage
  24 // of having a pool of threads, is faster performance. In particular, being
  25 // able to keep servicing PAC requests even if one blocks its execution.
  26 //
  27 // During initialization (CreateProxyResolver), a single thread is spun up to
  28 // test the script. If this succeeds, we cache the input script, and will re-use
  29 // this to lazily provision any new threads as needed.
  30 //
  31 // For each new thread that we spawn in a particular MultiThreadedProxyResolver
  32 // instance, a corresponding new ProxyResolver is created using the
  33 // ProxyResolverFactory returned by CreateProxyResolverFactory().
  34 //
  35 // Because we are creating multiple ProxyResolver instances, this means we
  36 // are duplicating script contexts for what is ordinarily seen as being a
  37 // single script. This can affect compatibility on some classes of PAC
  38 // script:
  39 //
  40 // (a) Scripts whose initialization has external dependencies on network or
  41 //     time may end up successfully initializing on some threads, but not
  42 //     others. So depending on what thread services the request, the result
  43 //     may jump between several possibilities.
  44 //
  45 // (b) Scripts whose FindProxyForURL() depends on side-effects may now
  46 //     work differently. For example, a PAC script which was incrementing
  47 //     a global counter and using that to make a decision. In the
  48 //     multi-threaded model, each thread may have a different value for this
  49 //     counter, so it won't globally be seen as monotonically increasing!
  50 class NET_EXPORT_PRIVATE MultiThreadedProxyResolverFactory
  51     : public ProxyResolverFactory {
  52  public:
  53   MultiThreadedProxyResolverFactory(size_t max_num_threads,
  54                                     bool factory_expects_bytes);
  55   ~MultiThreadedProxyResolverFactory() override;
  56
  57   int CreateProxyResolver(
  58       const scoped_refptr<ProxyResolverScriptData>& pac_script,
  59       scoped_ptr<ProxyResolver>* resolver,
  60       const CompletionCallback& callback,
  61       scoped_ptr<Request>* request) override;
  62
  63  private:
  64   class Job;
  65
  66   // Invoked to create a ProxyResolverFactory instance to pass to a
  67   // MultiThreadedProxyResolver instance.
  68   virtual scoped_ptr<ProxyResolverFactory> CreateProxyResolverFactory() = 0;
  69
  70   void RemoveJob(Job* job);
  71
  72   const size_t max_num_threads_;
  73
  74   std::set<Job*> jobs_;
  75 };
  76
  77 }  // namespace net
  78
  79 #endif  // NET_PROXY_MULTI_THREADED_PROXY_RESOLVER_H_