[Cronet] Add ExperimentalCronetEngine.Builder.setThreadPriority() API

components/cronet/android/java/src/org/chromium/net/impl/CronetEngineBuilderImpl.java

 // 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.
 package org.chromium.net.impl;
 
+import static android.os.Process.THREAD_PRIORITY_LOWEST;
+
 import android.content.Context;
 import android.support.annotation.IntDef;
 import android.support.annotation.VisibleForTesting;
 
 import static org.chromium.net.CronetEngine.Builder.HTTP_CACHE_DISABLED;
 import static org.chromium.net.CronetEngine.Builder.HTTP_CACHE_DISK;
 import static org.chromium.net.CronetEngine.Builder.HTTP_CACHE_DISK_NO_HTTP;
 import static org.chromium.net.CronetEngine.Builder.HTTP_CACHE_IN_MEMORY;
 
 import org.chromium.net.CronetEngine;
@@ skipping 48 matching lines @@
         Pkp(String host, byte[][] hashes, boolean includeSubdomains, Date expirationDate) {
             mHost = host;
             mHashes = hashes;
             mIncludeSubdomains = includeSubdomains;
             mExpirationDate = expirationDate;
         }
     }
 
     private static final Pattern INVALID_PKP_HOST_NAME = Pattern.compile("^[0-9\\.]*$");
 
+    private static final int INVALID_THREAD_PRIORITY = THREAD_PRIORITY_LOWEST + 1;
+
     // Private fields are simply storage of configuration for the resulting CronetEngine.
     // See setters below for verbose descriptions.
     private final Context mApplicationContext;
     private final List<QuicHint> mQuicHints = new LinkedList<>();
     private final List<Pkp> mPkps = new LinkedList<>();
     private boolean mPublicKeyPinningBypassForLocalTrustAnchorsEnabled;
     private String mUserAgent;
     private String mStoragePath;
     private VersionSafeCallbacks.LibraryLoader mLibraryLoader;
     private boolean mQuicEnabled;
     private boolean mHttp2Enabled;
     private boolean mSdchEnabled;
     private boolean mBrotiEnabled;
     private boolean mDisableCache;
     private int mHttpCacheMode;
     private long mHttpCacheMaxSize;
     private String mExperimentalOptions;
     protected long mMockCertVerifier;
     private boolean mNetworkQualityEstimatorEnabled;
     private String mCertVerifierData;
+    private int mThreadPriority = INVALID_THREAD_PRIORITY;
 
     /**
      * Default config enables SPDY, disables QUIC, SDCH and HTTP cache.
      * @param context Android {@link Context} for engine to use.
      */
     public CronetEngineBuilderImpl(Context context) {
         mApplicationContext = context.getApplicationContext();
         enableQuic(false);
         enableHttp2(true);
         enableSdch(false);
@@ skipping 276 matching lines @@
     @Override
     public CronetEngineBuilderImpl enableNetworkQualityEstimator(boolean value) {
         mNetworkQualityEstimatorEnabled = value;
         return this;
     }
 
     String certVerifierData() {
         return mCertVerifierData;
     }
 
+    @Override
+    public CronetEngineBuilderImpl setThreadPriority(int priority) {
+        if (priority > THREAD_PRIORITY_LOWEST || priority < -20) {
+            throw new IllegalArgumentException("Thread priority invalid");
+        }
+        mThreadPriority = priority;
+        return this;
+    }
+
+    /**
+     * @returns thread priority provided by user, or {@code defaultThreadPriority} if none provided.
+     */
+    int threadPriority(int defaultThreadPriority) {
+        return mThreadPriority == INVALID_THREAD_PRIORITY ? defaultThreadPriority : mThreadPriority;

[mef, 2017/05/15 17:20:11]

can we just default |mThreadPriority| to sensible defaultThreadPriority?

[pauljensen, 2017/05/15 19:03:25]

I feel that could have significant impact on performance.  I think we should
have an embedder experiment with the background+1 priority, and if that looks
good, then use it for the default.

[mef, 2017/05/16 15:51:29]

Sounds good, it makes sense to experiment.

+    }
+
     /**
      * Returns {@link Context} for builder.
      *
      * @return {@link Context} for builder.
      */
     Context getContext() {
         return mApplicationContext;
     }
 }