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// Copyright (c) 2011 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#ifndef NET_PROXY_MULTI_THREADED_PROXY_RESOLVER_H_
#define NET_PROXY_MULTI_THREADED_PROXY_RESOLVER_H_
#include <deque>
#include <vector>
#include "base/basictypes.h"
#include "base/memory/ref_counted.h"
#include "base/memory/scoped_ptr.h"
#include "base/threading/non_thread_safe.h"
#include "net/base/net_export.h"
#include "net/proxy/proxy_resolver.h"
namespace base {
class Thread;
} // namespace base
namespace net {
class ProxyResolverFactory;
// MultiThreadedProxyResolver is a ProxyResolver implementation that runs
// synchronous ProxyResolver implementations on worker threads.
//
// Threads are created lazily on demand, up to a maximum total. The advantage
// of having a pool of threads, is faster performance. In particular, being
// able to keep servicing PAC requests even if one blocks its execution.
//
// During initialization (SetPacScript), a single thread is spun up to test
// the script. If this succeeds, we cache the input script, and will re-use
// this to lazily provision any new threads as needed.
//
// For each new thread that we spawn, a corresponding new ProxyResolver is
// created using ProxyResolverFactory.
//
// Because we are creating multiple ProxyResolver instances, this means we
// are duplicating script contexts for what is ordinarily seen as being a
// single script. This can affect compatibility on some classes of PAC
// script:
//
// (a) Scripts whose initialization has external dependencies on network or
// time may end up successfully initializing on some threads, but not
// others. So depending on what thread services the request, the result
// may jump between several possibilities.
//
// (b) Scripts whose FindProxyForURL() depends on side-effects may now
// work differently. For example, a PAC script which was incrementing
// a global counter and using that to make a decision. In the
// multi-threaded model, each thread may have a different value for this
// counter, so it won't globally be seen as monotonically increasing!
class NET_EXPORT_PRIVATE MultiThreadedProxyResolver
: public ProxyResolver,
NON_EXPORTED_BASE(public base::NonThreadSafe) {
public:
// Creates an asynchronous ProxyResolver that runs requests on up to
// |max_num_threads|.
//
// For each thread that is created, an accompanying synchronous ProxyResolver
// will be provisioned using |resolver_factory|. All methods on these
// ProxyResolvers will be called on the one thread, with the exception of
// ProxyResolver::Shutdown() which will be called from the origin thread
// prior to destruction.
//
// The constructor takes ownership of |resolver_factory|.
MultiThreadedProxyResolver(ProxyResolverFactory* resolver_factory,
size_t max_num_threads);
~MultiThreadedProxyResolver() override;
// ProxyResolver implementation:
int GetProxyForURL(const GURL& url,
ProxyInfo* results,
const CompletionCallback& callback,
RequestHandle* request,
const BoundNetLog& net_log) override;
void CancelRequest(RequestHandle request) override;
LoadState GetLoadState(RequestHandle request) const override;
void CancelSetPacScript() override;
int SetPacScript(const scoped_refptr<ProxyResolverScriptData>& script_data,
const CompletionCallback& callback) override;
private:
class Executor;
class Job;
class SetPacScriptJob;
class GetProxyForURLJob;
// FIFO queue of pending jobs waiting to be started.
// TODO(eroman): Make this priority queue.
typedef std::deque<scoped_refptr<Job> > PendingJobsQueue;
typedef std::vector<scoped_refptr<Executor> > ExecutorList;
// Asserts that there are no outstanding user-initiated jobs on any of the
// worker threads.
void CheckNoOutstandingUserRequests() const;
// Stops and deletes all of the worker threads.
void ReleaseAllExecutors();
// Returns an idle worker thread which is ready to receive GetProxyForURL()
// requests. If all threads are occupied, returns NULL.
Executor* FindIdleExecutor();
// Creates a new worker thread, and appends it to |executors_|.
Executor* AddNewExecutor();
// Starts the next job from |pending_jobs_| if possible.
void OnExecutorReady(Executor* executor);
const scoped_ptr<ProxyResolverFactory> resolver_factory_;
const size_t max_num_threads_;
PendingJobsQueue pending_jobs_;
ExecutorList executors_;
scoped_refptr<ProxyResolverScriptData> current_script_data_;
};
} // namespace net
#endif // NET_PROXY_MULTI_THREADED_PROXY_RESOLVER_H_
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