Add pause/resume functionality to precache

components/precache/core/precache_database.h

 // Copyright 2013 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 COMPONENTS_PRECACHE_CORE_PRECACHE_DATABASE_H_
 #define COMPONENTS_PRECACHE_CORE_PRECACHE_DATABASE_H_
 
 #include <stdint.h>
 
+#include <list>
 #include <memory>
 #include <string>
 #include <vector>
 
 #include "base/callback.h"
 #include "base/containers/hash_tables.h"
 #include "base/macros.h"
+#include "base/memory/ref_counted.h"
 #include "base/memory/weak_ptr.h"
 #include "base/threading/thread_checker.h"
+#include "components/precache/core/precache_fetcher.h"
+#include "components/precache/core/precache_session_tables.h"
 #include "components/precache/core/precache_url_table.h"
 
 class GURL;
 
 namespace base {
 class FilePath;
 class Time;
 }
 
 namespace sql {
 class Connection;
 }
 
 namespace precache {
 
+// Represents the precache work that is left over after a precache session
+// is interrupted.
+class UnfinishedWork : public base::RefCountedThreadSafe<UnfinishedWork> {

[sclittle, 2016/05/10 00:01:26]

See my comment in precache_fetcher.cc about passing this around as a
std::unique_ptr instead of refcounting.

[bengr, 2016/05/19 01:25:44]

Done.

+ public:
+  // Constructor used when saving unfinished work to storage.
+  // |manifest_urls_to_fetch| and |resource_urls_to_fetch| are the
+  // remaining manifest and resource URLs to fetch. |total_response_bytes|
+  // and |network_response_bytes| are counts of bytes receieved, the former
+  // including bytes received from local cache. |num_manifest_urls_to_fetch|
+  // is the initial number of manifest URLs that needed to be fetched. The
+  // |start_time_of_session| is the time the precache session began, before
+  // any interruptions.
+  UnfinishedWork(const std::list<GURL>& manifest_urls_to_fetch,
+                 const std::list<GURL>& resource_urls_to_fetch,
+                 int64_t total_response_bytes,
+                 int64_t network_response_bytes,
+                 int64_t num_manifest_urls_to_fetch,
+                 const base::TimeTicks& start_time_of_session);
+
+  // Constructor used when retrieving unfinished work from storage. No work
+  // saved before |earliest_start_time_of_session| will be retrieved.
+  explicit UnfinishedWork(
+      const base::TimeTicks& earliest_start_time_of_session);
+
+  // Manifest URLs remaining to be fetched.
+  std::list<GURL> manifests;

[sclittle, 2016/05/10 00:01:26]

If you just have publicly visible members, then could you change UnfinishedWork
to be a struct instead of a class? Otherwise, you should add getters and setters
for each.

[bengr, 2016/05/19 01:25:44]

Done.

+
+  // Resource URLs remaining to be fetched.
+  std::list<GURL> resources;
+
+  // Count of the total received bytes.
+  int64_t total_bytes;
+
+  // Count of the total received bytes over the network.
+  int64_t network_bytes;
+
+  // The total number of manifest URLs that the precache session started with.
+  int64_t num_manifest_urls;
+
+  // The original time the precache session started, not the time it resumed.
+  base::TimeTicks start_time;

[sclittle, 2016/05/10 00:01:26]

Should this be base::Time instead? I don't think it's safe to compare
base::TimeTicks values between different sessions, especially if the device was
rebooted or something.

[bengr, 2016/05/19 01:25:44]

Done.

+
+ private:
+  friend class base::RefCountedThreadSafe<UnfinishedWork>;
+
+  ~UnfinishedWork();
+
+  DISALLOW_COPY_AND_ASSIGN(UnfinishedWork);
+};
+
 // Class that tracks information related to precaching. This class may be
 // constructed on any thread, but all calls to, and destruction of this class
 // must be done on the the DB thread.
 class PrecacheDatabase {
  public:
   // A PrecacheDatabase can be constructed on any thread.
   PrecacheDatabase();
 
   ~PrecacheDatabase();
 
@@ skipping 20 matching lines @@
   // the fetch was not motivated by precaching. |is_connection_cellular|
   // indicates whether the current network connection is a cellular network.
   void RecordURLNonPrefetch(const GURL& url,
                             const base::TimeDelta& latency,
                             const base::Time& fetch_time,
                             int64_t size,
                             bool was_cached,
                             int host_rank,
                             bool is_connection_cellular);
 
+  // Gets the state required to continue a precache session.
+  void GetUnfinishedWork(scoped_refptr<UnfinishedWork> unfinished_work);
+
+  // Stores the state required to continue a precache session so that the
+  // session can be resumed later.
+  void SaveUnfinishedWork(scoped_refptr<UnfinishedWork> unfinished_work);
+
+  // Clears all precache session state.
+  void ClearPrecacheSessionState();
+
+  base::WeakPtr<PrecacheDatabase> GetWeakPtr();
+
  private:
   friend class PrecacheDatabaseTest;
 
   bool IsDatabaseAccessible() const;
 
   // Flushes any buffered write operations. |buffered_writes_| will be empty
   // after calling this function. To maximize performance, all the buffered
   // writes are run in a single database transaction.
   void Flush();
 
   // Same as Flush(), but also updates the flag |is_flush_posted_| to indicate
   // that a flush is no longer posted.
   void PostedFlush();
 
   // Post a call to PostedFlush() on the current thread's MessageLoop, if
   // |buffered_writes_| is non-empty and there isn't already a flush call
   // posted.
   void MaybePostFlush();
 
   std::unique_ptr<sql::Connection> db_;
 
   // Table that keeps track of URLs that are in the cache because of precaching,
   // and wouldn't be in the cache otherwise. If |buffered_writes_| is non-empty,
   // then this table will not be up to date until the next call to Flush().
   PrecacheURLTable precache_url_table_;
 
+  // Tables that persist the state required to pause and resume a precache
+  // session.
+  PrecacheSessionTables precache_session_tables_;
+
   // A vector of write operations to be run on the database.
   std::vector<base::Closure> buffered_writes_;
 
   // Set of URLs that have been modified in |buffered_writes_|. It's a hash set
   // of strings, and not GURLs, because there is no hash function on GURL.
   base::hash_set<std::string> buffered_urls_;
 
   // Flag indicating whether or not a call to Flush() has been posted to run in
   // the future.
   bool is_flush_posted_;
 
   // ThreadChecker used to ensure that all methods other than the constructor
   // or destructor are called on the same thread.
   base::ThreadChecker thread_checker_;
 
   base::WeakPtrFactory<PrecacheDatabase> weak_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(PrecacheDatabase);
 };
 
 }  // namespace precache
 
 #endif  // COMPONENTS_PRECACHE_CORE_PRECACHE_DATABASE_H_