Selectively perform JNI registration in render processes on Android.

base/android/jni_android.h

 // Copyright (c) 2012 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.
 
 #ifndef BASE_ANDROID_JNI_ANDROID_H_
 #define BASE_ANDROID_JNI_ANDROID_H_
 
 #include <jni.h>
 #include <sys/types.h>
 
@@ skipping 36 matching lines @@
 #define JNI_LINK_SAVED_FRAME_POINTER
 
 #endif  // HAVE_TRACE_STACK_FRAME_POINTERS
 
 namespace base {
 namespace android {
 
 // Used to mark symbols to be exported in a shared library's symbol table.
 #define JNI_EXPORT __attribute__ ((visibility("default")))
 
+// The level of JNI registration required for the current process.
+// GENERATED_JAVA_ENUM_PACKAGE: org.chromium.base
+enum JniRegistrationType {
+  // Indicates the JNI registration type hasn't yet been set.
+  UNINITIALIZED_JNI_REGISTRATION,
+  // Register all native methods.
+  ALL_JNI_REGISTRATION,
+  // Register some native methods, as controlled by the jni_generator.
+  SELECTIVE_JNI_REGISTRATION,
+  // Do not register any native methods.
+  NO_JNI_REGISTRATION,
+};
+
 // Used to disable manual JNI registration in binaries that prefer to use native
-// JNI exports for startup performance. This is not compatible with the crazy
-// linker and so defaults to off. Call DisableManualJniRegistration at the very
-// beginning of JNI_OnLoad to use this.
-BASE_EXPORT bool IsManualJniRegistrationDisabled();
+// JNI exports for startup performance. Call DisableManualJniRegistration at
+// the very beginning of JNI_OnLoad to use this.
 BASE_EXPORT void DisableManualJniRegistration();

[Torne, 2017/01/30 12:29:56]

So with this change we do all registration by default, and the child process
services switch to selective before loading native.

Then, separately, the Monochrome/WebView entry points call this to override it
to none?

That should work and I get why it's easier to do it that way (since it's the
entrypoint of the native code that knows whether it's compiled to need
registration or not). It is slightly weird that the value on the java side and
the native side end up different though..

[estevenson, 2017/01/30 19:19:27]

We could remove JniRegistrationType from the Java side + change
JNIUtils.setJniRegistrationType(JniRegistrationType) and
JNIUtils.getJniRegistrationType() to JNIUtils.enableSelectiveJniRegistration()
and JNIUtils.isSelectiveJniRegistrationEnabled().

Then have ONLY the native side worry about JniRegistrationType and set it in
each *_entry_point for more consistency.

Still not optimal, but might be a small improvement, wdyt?

 
+// Gets the JniRegistrationType from Java and caches it on the native side.
+BASE_EXPORT JniRegistrationType FetchJniRegistrationType();
+
 // Contains the registration method information for initializing JNI bindings.
 struct RegistrationMethod {
   const char* name;
   bool (*func)(JNIEnv* env);
 };
 
 // Attaches the current thread to the VM (if necessary) and return the JNIEnv*.
 BASE_EXPORT JNIEnv* AttachCurrentThread();
 
 // Same to AttachCurrentThread except that thread name will be set to
@@ skipping 96 matching lines @@
 
   DISALLOW_COPY_AND_ASSIGN(JNIStackFrameSaver);
 };
 
 #endif  // HAVE_TRACE_STACK_FRAME_POINTERS
 
 }  // namespace android
 }  // namespace base
 
 #endif  // BASE_ANDROID_JNI_ANDROID_H_