Offer to write Strings through Parcels as UTF-8.

Recently while investigating some Binder limits, I discovered that
we're still sending Strings across Binder as UTF-16, which is very
wasteful for two reasons:

1. The majority of data flowing through APIs like PackageManager is
already limited to US-ASCII, and by sending UTF-16 we're wasting
half of our transactions on null-byte overhead.

2. Internally ART is already "compressing" simple strings by storing
them as US-ASCII instead of UTF-16, meaning every time we want to
write a simple string to Binder, we're forced to first inflate it
to UTF-16.

This change first updates Parcel.cpp to accept char* UTF-8 strings,
similar to how it accepts char16_t* for UTF-16.  It then offers
both UTF-8 and UTF-16 variants to Parcel.java via JNI.  We also
update the String8 handling to behave identical to String16.

This change adds benchmarking to show that these new methods are
about 50% faster for US-ASCII strings, and about 68% faster for
complex strings that reference higher Unicode planes.  (So an
improvement in both cases!)

Bug: 154436100
Test: atest FrameworksCoreTests:ParcelTest
Test: make core-libart conscrypt okhttp bouncycastle vogar caliper && vogar --mode app_process --benchmark frameworks/base/core/tests/benchmarks/src/android/os/ParcelStringBenchmark.java
Change-Id: I22a11d3497486d922ec8e14c85df66ca096b8f2a

1 files changed, 72 insertions, 0 deletions

diff --git a/core/tests/benchmarks/src/android/os/ParcelStringBenchmark.java b/core/tests/benchmarks/src/android/os/ParcelStringBenchmark.java
new file mode 100644
index 000000000000..daa90c28e0c4
--- /dev/null
+++ b/core/tests/benchmarks/src/android/os/ParcelStringBenchmark.java
@@ -0,0 +1,72 @@
+/*
+ * Copyright (C) 2020 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package android.os;
+
+import com.google.caliper.AfterExperiment;
+import com.google.caliper.BeforeExperiment;
+import com.google.caliper.Param;
+
+public class ParcelStringBenchmark {
+
+    @Param({"com.example.typical_package_name", "從不喜歡孤單一個 - 蘇永康／吳雨霏"})
+    String mValue;
+
+    private Parcel mParcel;
+
+    @BeforeExperiment
+    protected void setUp() {
+        mParcel = Parcel.obtain();
+    }
+
+    @AfterExperiment
+    protected void tearDown() {
+        mParcel.recycle();
+        mParcel = null;
+    }
+
+    public void timeWriteString8(int reps) {
+        for (int i = 0; i < reps; i++) {
+            mParcel.setDataPosition(0);
+            mParcel.writeString8(mValue);
+        }
+    }
+
+    public void timeReadString8(int reps) {
+        mParcel.writeString8(mValue);
+
+        for (int i = 0; i < reps; i++) {
+            mParcel.setDataPosition(0);
+            mParcel.readString8();
+        }
+    }
+
+    public void timeWriteString16(int reps) {
+        for (int i = 0; i < reps; i++) {
+            mParcel.setDataPosition(0);
+            mParcel.writeString16(mValue);
+        }
+    }
+
+    public void timeReadString16(int reps) {
+        mParcel.writeString16(mValue);
+
+        for (int i = 0; i < reps; i++) {
+            mParcel.setDataPosition(0);
+            mParcel.readString16();
+        }
+    }
+}