content/public/browser/download_id.h

   1 // Copyright (c) 2012 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 CONTENT_PUBLIC_BROWSER_DOWNLOAD_ID_H_
   6 #define CONTENT_PUBLIC_BROWSER_DOWNLOAD_ID_H_
   7
   8 #include <iosfwd>
   9 #include <string>
  10
  11 #include "base/containers/hash_tables.h"
  12 #include "base/strings/stringprintf.h"
  13 #include "content/common/content_export.h"
  14
  15 namespace content {
  16
  17 // DownloadId combines per-profile Download ids with an indication of which
  18 // profile in order to be globally unique. DownloadIds are not persistent across
  19 // sessions, but their local() field is.
  20 class DownloadId {
  21  public:
  22   static DownloadId Invalid() { return DownloadId(); }
  23
  24   // Domain separates spaces of local ids.
  25   typedef const void* Domain;
  26
  27   DownloadId() : domain_(NULL), local_id_(-1) {}
  28
  29   DownloadId(Domain domain, int32 local_id)
  30     : domain_(domain),
  31       local_id_(local_id) {
  32   }
  33
  34   // Return the per-profile and persistent part of this DownloadId.
  35   int32 local() const { return local_id_; }
  36
  37   // Returns true if this DownloadId has been allocated and could possibly refer
  38   // to a DownloadItem that exists.
  39   bool IsValid() const { return ((domain_ != NULL) && (local_id_ >= 0)); }
  40
  41   // The following methods (operator==, hash(), copy, and assign) provide
  42   // support for STL containers such as hash_map.
  43
  44   bool operator==(const DownloadId& that) const {
  45     return ((that.local_id_ == local_id_) &&
  46             (that.domain_ == domain_));
  47   }
  48   bool operator<(const DownloadId& that) const {
  49     // Even though Domain::operator< is not well defined and
  50     // GCC does not require it for hash_map, MSVC requires operator< for
  51     // hash_map. We don't ifdef it out here because we will probably make a
  52     // set<DownloadId> at some point, when GCC will require it.
  53     return ((domain_ < that.domain_) ||
  54             ((domain_ == that.domain_) && (local_id_ < that.local_id_)));
  55   }
  56
  57   size_t hash() const {
  58     // The top half of domain_ is unlikely to be distinct, and the user is
  59     // unlikely to have >64K downloads. If these assumptions are incorrect, then
  60     // hash_maps containing DownloadIds might have a few collisions, but can
  61     // use operator== to safely disambiguate.
  62     return reinterpret_cast<size_t>(domain_) +
  63            (static_cast<size_t>(local_id_) << (4 * sizeof(size_t)));
  64   }
  65
  66   std::string DebugString() const {
  67     return base::StringPrintf("%p:%d", domain_, local_id_);
  68   }
  69
  70  private:
  71   Domain domain_;
  72
  73   int32 local_id_;
  74
  75   // Allow copy and assign.
  76 };
  77
  78 }  // namespace content
  79
  80 // Allow logging DownloadIds. Looks like "0x01234567:42".
  81 CONTENT_EXPORT std::ostream& operator<<(std::ostream& out,
  82                                         const content::DownloadId& global_id);
  83 inline std::ostream& operator<<(std::ostream& out,
  84                                 const content::DownloadId& global_id) {
  85   return out << global_id.DebugString();
  86 }
  87
  88 // Allow using DownloadIds as keys in hash_maps.
  89 namespace BASE_HASH_NAMESPACE {
  90 #if defined(COMPILER_GCC)
  91 template<> struct hash<content::DownloadId> {
  92   std::size_t operator()(const content::DownloadId& id) const {
  93     return id.hash();
  94   }
  95 };
  96 #elif defined(COMPILER_MSVC)
  97 inline size_t hash_value(const content::DownloadId& id) {
  98   return id.hash();
  99 }
 100 #endif  // COMPILER
 101 }
 102 #endif  // CONTENT_PUBLIC_BROWSER_DOWNLOAD_ID_H_