yoga/lib/fb/jni/Environment.cpp

/*
 * Copyright (c) 2015-present, Facebook, Inc.
 * All rights reserved.
 *
 * This source code is licensed under the BSD-style license found in the
 * LICENSE file in the root directory of this source tree. An additional grant
 * of patent rights can be found in the PATENTS file in the same directory.
 */

#include <pthread.h>
#include <fb/log.h>
#include <fb/StaticInitialized.h>
#include <fb/ThreadLocal.h>
#include <fb/Environment.h>
#include <fb/fbjni/CoreClasses.h>
#include <fb/fbjni/NativeRunnable.h>

#include <functional>

namespace facebook {
namespace jni {

namespace {
StaticInitialized<ThreadLocal<JNIEnv>> g_env;
JavaVM* g_vm = nullptr;

struct JThreadScopeSupport : JavaClass<JThreadScopeSupport> {
  static auto constexpr kJavaDescriptor = "Lcom/facebook/jni/ThreadScopeSupport;";

  // These reinterpret_casts are a totally dangerous pattern. Don't use them. Use HybridData instead.
  static void runStdFunction(std::function<void()>&& func) {
    static auto method = javaClassStatic()->getStaticMethod<void(jlong)>("runStdFunction");
    method(javaClassStatic(), reinterpret_cast<jlong>(&func));
  }

  static void runStdFunctionImpl(alias_ref<JClass>, jlong ptr) {
    (*reinterpret_cast<std::function<void()>*>(ptr))();
  }

  static void OnLoad() {
    // We need the javaClassStatic so that the class lookup is cached and that
    // runStdFunction can be called from a ThreadScope-attached thread.
    javaClassStatic()->registerNatives({
        makeNativeMethod("runStdFunctionImpl", runStdFunctionImpl),
      });
  }
};
}

/* static */
JNIEnv* Environment::current() {
  JNIEnv* env = g_env->get();
  if ((env == nullptr) && (g_vm != nullptr)) {
    if (g_vm->GetEnv((void**) &env, JNI_VERSION_1_6) != JNI_OK) {
      FBLOGE("Error retrieving JNI Environment, thread is probably not attached to JVM");
      // TODO(cjhopman): This should throw an exception.
      env = nullptr;
    } else {
      g_env->reset(env);
    }
  }
  return env;
}

/* static */
void Environment::detachCurrentThread() {
  auto env = g_env->get();
  if (env) {
    FBASSERT(g_vm);
    g_vm->DetachCurrentThread();
    g_env->reset();
  }
}

struct EnvironmentInitializer {
  EnvironmentInitializer(JavaVM* vm) {
      FBASSERT(!g_vm);
      FBASSERT(vm);
      g_vm = vm;
      g_env.initialize([] (void*) {});
  }
};

/* static */
void Environment::initialize(JavaVM* vm) {
  static EnvironmentInitializer init(vm);
}

/* static */
JNIEnv* Environment::ensureCurrentThreadIsAttached() {
  auto env = g_env->get();
  if (!env) {
    FBASSERT(g_vm);
    g_vm->AttachCurrentThread(&env, nullptr);
    g_env->reset(env);
  }
  return env;
}

ThreadScope::ThreadScope()
    : attachedWithThisScope_(false) {
  JNIEnv* env = nullptr;
  if (g_vm->GetEnv((void**) &env, JNI_VERSION_1_6) != JNI_EDETACHED) {
    return;
  }
  env = facebook::jni::Environment::ensureCurrentThreadIsAttached();
  FBASSERT(env);
  attachedWithThisScope_ = true;
}

ThreadScope::~ThreadScope() {
  if (attachedWithThisScope_) {
    Environment::detachCurrentThread();
  }
}

/* static */
void ThreadScope::OnLoad() {
  // These classes are required for ScopeWithClassLoader. Ensure they are looked up when loading.
  JThreadScopeSupport::OnLoad();
}

/* static */
void ThreadScope::WithClassLoader(std::function<void()>&& runnable) {
  // TODO(cjhopman): If the classloader is already available in this scope, we
  // shouldn't have to jump through java.
  ThreadScope ts;
  JThreadScopeSupport::runStdFunction(std::move(runnable));
}

} }