SERVER-36108 speed up BSONArrayBuilder by counting in decimal

Now removed constexpr that broke Windows build.

3 files changed, 96 insertions, 36 deletions

diff --git a/src/mongo/bson/SConscript b/src/mongo/bson/SConscript
index fbe9ef1dae0..f1d9ab122ea 100644
--- a/src/mongo/bson/SConscript
+++ b/src/mongo/bson/SConscript
@@ -65,6 +65,16 @@ env.CppUnitTest(
     ],
 )
 
+env.Benchmark(
+    target='bsonobjbuilder_bm',
+    source=[
+        'bsonobjbuilder_bm.cpp',
+    ],
+    LIBDEPS=[
+        '$BUILD_DIR/mongo/base',
+    ],
+)
+
 env.CppUnitTest(
     target='bsonelement_test',
     source=[
diff --git a/src/mongo/bson/bsonobjbuilder.h b/src/mongo/bson/bsonobjbuilder.h
index 6162495c1cd..ef92065d9a0 100644
--- a/src/mongo/bson/bsonobjbuilder.h
+++ b/src/mongo/bson/bsonobjbuilder.h
@@ -48,7 +48,7 @@
 #include "mongo/bson/util/builder.h"
 #include "mongo/platform/decimal128.h"
 #include "mongo/stdx/type_traits.h"
-#include "mongo/util/itoa.h"
+#include "mongo/util/decimal_counter.h"
 
 namespace mongo {
 
@@ -810,20 +810,20 @@ private:
 
 class BSONArrayBuilder {
 public:
-    BSONArrayBuilder() : _i(0), _b() {}
-    BSONArrayBuilder(BufBuilder& _b) : _i(0), _b(_b) {}
-    BSONArrayBuilder(int initialSize) : _i(0), _b(initialSize) {}
+    BSONArrayBuilder() {}
+    BSONArrayBuilder(BufBuilder& _b) : _b(_b) {}
+    BSONArrayBuilder(int initialSize) : _b(initialSize) {}
 
     template <typename T>
     BSONArrayBuilder& append(const T& x) {
-        ItoA itoa(_i++);
-        _b.append(itoa, x);
+        _b.append(_fieldCount, x);
+        ++_fieldCount;
         return *this;
     }
 
     BSONArrayBuilder& append(const BSONElement& e) {
-        ItoA itoa(_i++);
-        _b.appendAs(e, itoa);
+        _b.appendAs(e, _fieldCount);
+        ++_fieldCount;
         return *this;
     }
 
@@ -833,19 +833,19 @@ public:
 
     template <typename T>
     BSONArrayBuilder& operator<<(const T& x) {
-        ItoA itoa(_i++);
-        _b << itoa << x;
+        _b << _fieldCount << x;
+        ++_fieldCount;
         return *this;
     }
 
     void appendNull() {
-        ItoA itoa(_i++);
-        _b.appendNull(itoa);
+        _b.appendNull(_fieldCount);
+        ++_fieldCount;
     }
 
     void appendUndefined() {
-        ItoA itoa(_i++);
-        _b.appendUndefined(itoa);
+        _b.appendUndefined(_fieldCount);
+        ++_fieldCount;
     }
 
     /**
@@ -875,59 +875,57 @@ public:
 
     // These two just use next position
     BufBuilder& subobjStart() {
-        ItoA itoa(_i++);
-        return _b.subobjStart(itoa);
+        return _b.subobjStart(_fieldCount++);
     }
     BufBuilder& subarrayStart() {
-        ItoA itoa(_i++);
-        return _b.subarrayStart(itoa);
+        return _b.subarrayStart(_fieldCount++);
     }
 
     BSONArrayBuilder& appendRegex(StringData regex, StringData options = "") {
-        ItoA itoa(_i++);
-        _b.appendRegex(itoa, regex, options);
+        _b.appendRegex(_fieldCount, regex, options);
+        ++_fieldCount;
         return *this;
     }
 
     BSONArrayBuilder& appendBinData(int len, BinDataType type, const void* data) {
-        ItoA itoa(_i++);
-        _b.appendBinData(itoa, len, type, data);
+        _b.appendBinData(_fieldCount, len, type, data);
+        ++_fieldCount;
         return *this;
     }
 
     BSONArrayBuilder& appendCode(StringData code) {
-        ItoA itoa(_i++);
-        _b.appendCode(itoa, code);
+        _b.appendCode(_fieldCount, code);
+        ++_fieldCount;
         return *this;
     }
 
     BSONArrayBuilder& appendCodeWScope(StringData code, const BSONObj& scope) {
-        ItoA itoa(_i++);
-        _b.appendCodeWScope(itoa, code, scope);
+        _b.appendCodeWScope(_fieldCount, code, scope);
+        ++_fieldCount;
         return *this;
     }
 
     BSONArrayBuilder& appendTimeT(time_t dt) {
-        ItoA itoa(_i++);
-        _b.appendTimeT(itoa, dt);
+        _b.appendTimeT(_fieldCount, dt);
+        ++_fieldCount;
         return *this;
     }
 
     BSONArrayBuilder& appendDate(Date_t dt) {
-        ItoA itoa(_i++);
-        _b.appendDate(itoa, dt);
+        _b.appendDate(_fieldCount, dt);
+        ++_fieldCount;
         return *this;
     }
 
     BSONArrayBuilder& appendBool(bool val) {
-        ItoA itoa(_i++);
-        _b.appendBool(itoa, val);
+        _b.appendBool(_fieldCount, val);
+        ++_fieldCount;
         return *this;
     }
 
     BSONArrayBuilder& appendTimestamp(unsigned long long ts) {
-        ItoA itoa(_i++);
-        _b.appendTimestamp(itoa, ts);
+        _b.appendTimestamp(_fieldCount, ts);
+        ++_fieldCount;
         return *this;
     }
 
@@ -939,7 +937,7 @@ public:
         return _b.len();
     }
     int arrSize() const {
-        return _i;
+        return _fieldCount;
     }
 
     BufBuilder& bb() {
@@ -947,7 +945,7 @@ public:
     }
 
 private:
-    std::uint32_t _i;
+    DecimalCounter<uint32_t> _fieldCount;
     BSONObjBuilder _b;
 };
 
diff --git a/src/mongo/bson/bsonobjbuilder_bm.cpp b/src/mongo/bson/bsonobjbuilder_bm.cpp
new file mode 100644
index 00000000000..53410f72615
--- /dev/null
+++ b/src/mongo/bson/bsonobjbuilder_bm.cpp
@@ -0,0 +1,52 @@
+/**
+ *    Copyright (C) 2018 MongoDB Inc.
+ *
+ *    This program is free software: you can redistribute it and/or  modify
+ *    it under the terms of the GNU Affero General Public License, version 3,
+ *    as published by the Free Software Foundation.
+ *
+ *    This program is distributed in the hope that it will be useful,
+ *    but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *    GNU Affero General Public License for more details.
+ *
+ *    You should have received a copy of the GNU Affero General Public License
+ *    along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ *    As a special exception, the copyright holders give permission to link the
+ *    code of portions of this program with the OpenSSL library under certain
+ *    conditions as described in each individual source file and distribute
+ *    linked combinations including the program with the OpenSSL library. You
+ *    must comply with the GNU Affero General Public License in all respects for
+ *    all of the code used other than as permitted herein. If you modify file(s)
+ *    with this exception, you may extend this exception to your version of the
+ *    file(s), but you are not obligated to do so. If you do not wish to do so,
+ *    delete this exception statement from your version. If you delete this
+ *    exception statement from all source files in the program, then also delete
+ *    it in the license file.
+ */
+
+#include "mongo/platform/basic.h"
+
+#include <benchmark/benchmark.h>
+
+#include "mongo/bson/bsonobjbuilder.h"
+
+namespace mongo {
+
+void BM_arrayBuilder(benchmark::State& state) {
+    size_t totalBytes = 0;
+    for (auto _ : state) {
+        benchmark::ClobberMemory();
+        BSONArrayBuilder array;
+        for (auto j = 0; j < state.range(0); j++)
+            array.append(j);
+        totalBytes += array.len();
+        benchmark::DoNotOptimize(array.done());
+    }
+    state.SetBytesProcessed(totalBytes);
+}
+
+BENCHMARK(BM_arrayBuilder)->Ranges({{{1}, {100'000}}});
+
+}  // namespace mongo