274 lines
7.9 KiB
C++
274 lines
7.9 KiB
C++
/*
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* Copyright (C) 2008 The Android Open Source Project
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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#define LOG_TAG "PlatformLibrary"
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#include "utils/Log.h"
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#include <stdlib.h>
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#include <string.h>
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#include <unistd.h>
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#include <assert.h>
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#include "jni.h"
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// ----------------------------------------------------------------------------
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/*
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* Field/method IDs and class object references.
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*
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* You should not need to store the JNIEnv pointer in here. It is
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* thread-specific and will be passed back in on every call.
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*/
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static struct {
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jclass platformLibraryClass;
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jfieldID jniInt;
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jmethodID yodel;
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} gCachedState;
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// ----------------------------------------------------------------------------
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/*
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* Helper function to throw an arbitrary exception.
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*
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* Takes the exception class name, a format string, and one optional integer
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* argument (useful for including an error code, perhaps from errno).
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*/
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static void throwException(JNIEnv* env, const char* ex, const char* fmt,
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int data) {
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if (jclass cls = env->FindClass(ex)) {
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if (fmt != NULL) {
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char msg[1000];
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snprintf(msg, sizeof(msg), fmt, data);
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env->ThrowNew(cls, msg);
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} else {
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env->ThrowNew(cls, NULL);
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}
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/*
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* This is usually not necessary -- local references are released
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* automatically when the native code returns to the VM. It's
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* required if the code doesn't actually return, e.g. it's sitting
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* in a native event loop.
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*/
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env->DeleteLocalRef(cls);
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}
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}
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/*
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* Trivial sample method.
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*
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* If "bad" is true, this throws an exception. Otherwise, this sets the
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* "mJniInt" field to 42 and returns 24.
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*/
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static jint PlatformLibrary_getJniInt(JNIEnv* env, jobject thiz, jboolean bad) {
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if (bad) {
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throwException(env, "java/lang/IllegalStateException",
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"you are bad", 0);
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return 0; /* return value will be ignored */
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}
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env->SetIntField(thiz, gCachedState.jniInt, 42);
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return (jint)24;
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}
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/*
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* A more complex sample method.
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*
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* This takes a String as an argument, and returns a new String with
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* characters in reverse order. The new string is passed to another method.
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* This demonstrates basic String manipulation functions and method
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* invocation.
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*
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* This method is declared "static", so there's no "this" pointer; instead,
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* we get a pointer to the class object.
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*/
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static jstring PlatformLibrary_reverseString(JNIEnv* env, jclass clazz,
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jstring str) {
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if (str == NULL) {
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throwException(env, "java/lang/NullPointerException", NULL, 0);
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return NULL;
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}
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/*
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* Get a pointer to the string's UTF-16 character data. The data
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* may be a copy or a pointer to the original. Since String data
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* is immutable, we're not allowed to touch it.
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*/
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const jchar* strChars = env->GetStringChars(str, NULL);
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if (strChars == NULL) {
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/* something went wrong */
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ALOGW("Couldn't get string chars\n");
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return NULL;
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}
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jsize strLength = env->GetStringLength(str);
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/*
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* Write a progress message to the log. Log messages are UTF-8, so
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* we want to convert the string to show it.
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*/
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const char* printable = env->GetStringUTFChars(str, NULL);
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if (printable != NULL) {
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ALOGD("Reversing string '%s'\n", printable);
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env->ReleaseStringUTFChars(str, printable);
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}
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/*
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* Copy the characters to temporary storage, reversing as we go.
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*/
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jchar tempChars[strLength];
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for (int i = 0; i < strLength; i++) {
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tempChars[i] = strChars[strLength -1 -i];
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}
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/*
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* Release the original String. That way, if something fails later on,
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* we don't have to worry about this leading to a memory leak.
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*/
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env->ReleaseStringChars(str, strChars);
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strChars = NULL; /* this pointer no longer valid */
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/*
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* Create a new String with the chars.
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*/
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jstring result = env->NewString(tempChars, strLength);
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if (result == NULL) {
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ALOGE("NewString failed\n");
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return NULL;
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}
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/*
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* Now let's do something with it. We already have the methodID for
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* "yodel", so we can invoke it directly. It's in our class, so we
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* can use the Class object reference that was passed in.
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*/
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env->CallStaticVoidMethod(clazz, gCachedState.yodel, result);
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return result;
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}
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// ----------------------------------------------------------------------------
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/*
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* Array of methods.
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*
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* Each entry has three fields: the name of the method, the method
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* signature, and a pointer to the native implementation.
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*/
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static const JNINativeMethod gMethods[] = {
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{ "getJniInt", "(Z)I",
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(void*)PlatformLibrary_getJniInt },
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{ "reverseString", "(Ljava/lang/String;)Ljava/lang/String;",
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(void*)PlatformLibrary_reverseString },
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};
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/*
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* Do some (slow-ish) lookups now and save the results.
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*
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* Returns 0 on success.
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*/
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static int cacheIds(JNIEnv* env, jclass clazz) {
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/*
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* Save the class in case we want to use it later. Because this is a
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* reference to the Class object, we need to convert it to a JNI global
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* reference.
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*/
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gCachedState.platformLibraryClass = (jclass) env->NewGlobalRef(clazz);
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if (clazz == NULL) {
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ALOGE("Can't create new global ref\n");
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return -1;
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}
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/*
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* Cache field and method IDs. IDs are not references, which means we
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* don't need to call NewGlobalRef on them.
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*/
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gCachedState.jniInt = env->GetFieldID(clazz, "mJniInt", "I");
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if (gCachedState.jniInt == NULL) {
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ALOGE("Can't find PlatformLibrary.mJniInt\n");
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return -1;
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}
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gCachedState.yodel = env->GetStaticMethodID(clazz, "yodel",
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"(Ljava/lang/String;)V");
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if (gCachedState.yodel == NULL) {
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ALOGE("Can't find PlatformLibrary.yodel\n");
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return -1;
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}
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return 0;
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}
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/*
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* Explicitly register all methods for our class.
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*
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* While we're at it, cache some class references and method/field IDs.
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*
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* Returns 0 on success.
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*/
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static int registerMethods(JNIEnv* env) {
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static const char* const kClassName =
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"com/example/android/platform_library/PlatformLibrary";
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jclass clazz;
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/* look up the class */
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clazz = env->FindClass(kClassName);
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if (clazz == NULL) {
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ALOGE("Can't find class %s\n", kClassName);
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return -1;
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}
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/* register all the methods */
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if (env->RegisterNatives(clazz, gMethods,
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sizeof(gMethods) / sizeof(gMethods[0])) != JNI_OK)
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{
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ALOGE("Failed registering methods for %s\n", kClassName);
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return -1;
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}
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/* fill out the rest of the ID cache */
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return cacheIds(env, clazz);
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}
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// ----------------------------------------------------------------------------
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/*
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* This is called by the VM when the shared library is first loaded.
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*/
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jint JNI_OnLoad(JavaVM* vm, void* /*reserved*/) {
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JNIEnv* env = NULL;
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jint result = -1;
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if (vm->GetEnv((void**) &env, JNI_VERSION_1_4) != JNI_OK) {
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ALOGE("ERROR: GetEnv failed\n");
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goto bail;
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}
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assert(env != NULL);
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if (registerMethods(env) != 0) {
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ALOGE("ERROR: PlatformLibrary native registration failed\n");
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goto bail;
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}
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/* success -- return valid version number */
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result = JNI_VERSION_1_4;
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bail:
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return result;
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}
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