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51 lines
1.8 KiB
C++
51 lines
1.8 KiB
C++
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// Copyright 2018 The Chromium Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style license that can be
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// found in the LICENSE file.
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#include "base/metrics/ukm_source_id.h"
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#include "base/atomic_sequence_num.h"
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#include "base/logging.h"
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#include "base/rand_util.h"
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namespace base {
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namespace {
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const int64_t kLowBitsMask = (INT64_C(1) << 32) - 1;
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const int64_t kNumTypeBits = 2;
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const int64_t kTypeMask = (INT64_C(1) << kNumTypeBits) - 1;
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} // namespace
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// static
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UkmSourceId UkmSourceId::New() {
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// Generate some bits which are unique to this process, so we can generate
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// IDs independently in different processes. IDs generated by this method may
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// collide, but it should be sufficiently rare enough to not impact data
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// quality.
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const static int64_t process_id_bits =
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static_cast<int64_t>(RandUint64()) & ~kLowBitsMask;
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// Generate some bits which are unique within the process, using a counter.
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static AtomicSequenceNumber seq;
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UkmSourceId local_id = FromOtherId(seq.GetNext() + 1, UkmSourceId::Type::UKM);
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// Combine the local and process bits to generate a unique ID.
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return UkmSourceId((local_id.value_ & kLowBitsMask) | process_id_bits);
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}
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// static
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UkmSourceId UkmSourceId::FromOtherId(int64_t other_id, UkmSourceId::Type type) {
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const int64_t type_bits = static_cast<int64_t>(type);
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DCHECK_EQ(type_bits, type_bits & kTypeMask);
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// Stores the the type ID in the low bits of the source id, and shift the rest
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// of the ID to make room. This could cause the original ID to overflow, but
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// that should be rare enough that it won't matter for UKM's purposes.
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return UkmSourceId((other_id << kNumTypeBits) | type_bits);
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}
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UkmSourceId::Type UkmSourceId::GetType() const {
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return static_cast<UkmSourceId::Type>(value_ & kTypeMask);
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}
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} // namespace base
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