1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
|
// Copyright 2018 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#include "components/sessions/core/session_id_generator.h"
#include <ostream>
#include "base/functional/bind.h"
#include "base/metrics/histogram_functions.h"
#include "base/rand_util.h"
#include "components/prefs/pref_registry_simple.h"
#include "components/prefs/pref_service.h"
namespace sessions {
namespace {
const char kLastValuePref[] = "session_id_generator_last_value";
// On startup, we increment the internal counter by |kCautionaryIdPadding| to
// mitigate issues during ungraceful shutdown, where prefs might not have
// managed to persist the latest generated session IDs, but other databases
// (e.g. sync) might have stored those IDs.
const int kCautionaryIdPadding = 50;
SessionID::id_type DefaultRandGenerator() {
return base::RandGenerator(std::numeric_limits<SessionID::id_type>::max());
}
} // namespace
// static
SessionIdGenerator* SessionIdGenerator::GetInstance() {
return base::Singleton<SessionIdGenerator>::get();
}
// static
void SessionIdGenerator::RegisterPrefs(PrefRegistrySimple* prefs) {
prefs->RegisterInt64Pref(kLastValuePref, 0);
}
void SessionIdGenerator::Init(PrefService* local_state) {
DCHECK(local_state);
DCHECK(!local_state_);
DCHECK_EQ(0, last_value_) << "NewUnique() used before Init()";
local_state_ = local_state;
last_value_ = local_state_->GetInt64(kLastValuePref);
if (last_value_ <= 0) {
last_value_ = rand_generator_.Run();
}
// Increment by a constant to mitigate issues during ungraceful shutdown,
// where prefs might not have managed to persist the latest generated session
// IDs, but other databases (e.g. sync) might have stored those IDs.
IncrementValueBy(kCautionaryIdPadding);
}
void SessionIdGenerator::Shutdown() {
local_state_ = nullptr;
last_value_ = 0;
}
SessionID SessionIdGenerator::NewUnique() {
DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_);
IncrementValueBy(1);
DCHECK(SessionID::IsValidValue(last_value_));
return SessionID::FromSerializedValue(last_value_);
}
void SessionIdGenerator::SetHighestRestoredID(SessionID highest_restored_id) {
DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_);
SessionID::id_type difference = 0;
if (last_value_ < highest_restored_id.id() &&
highest_restored_id.id() - last_value_ <
std::numeric_limits<SessionID::id_type>::max() / 2) {
// Only do the check if the two numbers are not too far apart to prevent
// issues when the `last_value_` is looping back to 0.
difference = highest_restored_id.id() - last_value_;
IncrementValueBy(difference);
}
base::UmaHistogramCounts100("Session.ID.RestoredDifference", difference);
}
// static
std::string SessionIdGenerator::GetLastValuePrefNameForTest() {
return kLastValuePref;
}
void SessionIdGenerator::SetRandomGeneratorForTest(
const RandomGenerator& rand_generator) {
rand_generator_ = rand_generator;
}
SessionIdGenerator::SessionIdGenerator()
: local_state_(nullptr),
last_value_(0),
rand_generator_(base::BindRepeating(&DefaultRandGenerator)) {}
SessionIdGenerator::~SessionIdGenerator() = default;
void SessionIdGenerator::IncrementValueBy(int increment) {
DCHECK_LT(0, increment);
DCHECK_LE(0, last_value_);
if (last_value_ >
std::numeric_limits<SessionID::id_type>::max() - increment) {
last_value_ = 0;
}
last_value_ += increment;
// Init() should have been called in production (which initializes
// |local_state_|), but for test convenience, we allow operating even without
// underlying prefs.
if (local_state_) {
local_state_->SetInt64(kLastValuePref, last_value_);
}
}
bool SessionIdGenerator::IsInitializedForTest() const {
return local_state_ != nullptr;
}
} // namespace sessions
|
