Improved iterator for persistent memory allocator.

base/metrics/persistent_sample_map.cc

 // Copyright 2016 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.
 
 #include "base/metrics/persistent_sample_map.h"
 
 #include "base/logging.h"
 #include "base/memory/ptr_util.h"
 #include "base/stl_util.h"
 
@@ skipping 78 matching lines @@
 // The type-id used to identify sample records inside an allocator.
 const uint32_t kTypeIdSampleRecord = 0x8FE6A69F + 1;  // SHA1(SampleRecord) v1
 
 }  // namespace
 
 PersistentSampleMap::PersistentSampleMap(
     uint64_t id,
     PersistentMemoryAllocator* allocator,
     Metadata* meta)
     : HistogramSamples(id, meta),
-      allocator_(allocator) {
-  // This is created once but will continue to return new iterables even when
-  // it has previously reached the end.
-  allocator->CreateIterator(&sample_iter_);
-
+      allocator_(allocator),
+      sample_iter_(allocator) {
   // Load all existing samples during construction. It's no worse to do it
   // here than at some point in the future and could be better if construction
   // takes place on some background thread. New samples could be created at
   // any time by parallel threads; if so, they'll get loaded when needed.
   ImportSamples(kAllSamples);
 }
 
 PersistentSampleMap::~PersistentSampleMap() {}
 
 void PersistentSampleMap::Accumulate(Sample value, Count count) {
@@ skipping 110 matching lines @@
   // relatively small, as is the current case.
   //
   // However, it is not so good for objects that are created, detroyed, and
   // recreated on a periodic basis, such as when making a snapshot of
   // sparse histograms owned by another, ongoing process. In that case, the
   // entire cost is compressed into a single sequential operation... on the
   // UI thread no less.
   //
   // This will be addressed in a future CL.
 
-  uint32_t type_id;
   PersistentMemoryAllocator::Reference ref;
-  while ((ref = allocator_->GetNextIterable(&sample_iter_, &type_id)) != 0) {
-    if (type_id == kTypeIdSampleRecord) {
-      SampleRecord* record =
-          allocator_->GetAsObject<SampleRecord>(ref, kTypeIdSampleRecord);
-      if (!record)
-        continue;
+  while ((ref = sample_iter_.GetNextOfType(kTypeIdSampleRecord)) != 0) {
+    SampleRecord* record =
+        allocator_->GetAsObject<SampleRecord>(ref, kTypeIdSampleRecord);
+    if (!record)
+      continue;
 
-      // A sample record has been found but may not be for this histogram.
-      if (record->id != id())
-        continue;
+    // A sample record has been found but may not be for this histogram.
+    if (record->id != id())
+      continue;
 
-      // Check if the record's value is already known.
-      if (!ContainsKey(sample_counts_, record->value)) {
-        // No: Add it to map of known values if the value is valid.
-        if (record->value >= 0)
-          sample_counts_[record->value] = &record->count;
-      } else {
-        // Yes: Ignore it; it's a duplicate caused by a race condition -- see
-        // code & comment in GetOrCreateSampleCountStorage() for details.
-        // Check that nothing ever operated on the duplicate record.
-        DCHECK_EQ(0, record->count);
-      }
+    // Check if the record's value is already known.
+    if (!ContainsKey(sample_counts_, record->value)) {
+      // No: Add it to map of known values if the value is valid.
+      if (record->value >= 0)
+        sample_counts_[record->value] = &record->count;
+    } else {
+      // Yes: Ignore it; it's a duplicate caused by a race condition -- see
+      // code & comment in GetOrCreateSampleCountStorage() for details.
+      // Check that nothing ever operated on the duplicate record.
+      DCHECK_EQ(0, record->count);
+    }
 
-      // Stop if it's the value being searched for.
-      if (record->value == until_value)
-        return &record->count;
-    }
+    // Stop if it's the value being searched for.
+    if (record->value == until_value)
+      return &record->count;
   }
 
   return nullptr;
 }
 
 }  // namespace base