android JNIEnv实现

当用到JNI时，总不明白JNIEnv这个东东是个啥，有啥用；这次总算在源码中找到了它的实现，做个记录。。。。

android_source_code_dir\dalvik\libnativehelper\include\nativehelper\Jni.h

/*
 * C++ object wrapper.
 *
 * This is usually overlaid on a C struct whose first element is a
 * JNINativeInterface*.  We rely somewhat on compiler behavior.
 */
struct _JNIEnv {
    /* do not rename this; it does not seem to be entirely opaque */
    const struct JNINativeInterface* functions;

#if defined(__cplusplus)

    jint GetVersion()
    { return functions->GetVersion(this); }

    jclass DefineClass(const char *name, jobject loader, const jbyte* buf,
        jsize bufLen)
    { return functions->DefineClass(this, name, loader, buf, bufLen); }

    jclass FindClass(const char* name)
    { return functions->FindClass(this, name); }

    jmethodID FromReflectedMethod(jobject method)
    { return functions->FromReflectedMethod(this, method); }

    jfieldID FromReflectedField(jobject field)
    { return functions->FromReflectedField(this, field); }

    jobject ToReflectedMethod(jclass cls, jmethodID methodID, jboolean isStatic)
    { return functions->ToReflectedMethod(this, cls, methodID, isStatic); }

    jclass GetSuperclass(jclass clazz)
    { return functions->GetSuperclass(this, clazz); }

    jboolean IsAssignableFrom(jclass clazz1, jclass clazz2)
    { return functions->IsAssignableFrom(this, clazz1, clazz2); }

    jobject ToReflectedField(jclass cls, jfieldID fieldID, jboolean isStatic)
    { return functions->ToReflectedField(this, cls, fieldID, isStatic); }

    jint Throw(jthrowable obj)
    { return functions->Throw(this, obj); }

    jint ThrowNew(jclass clazz, const char* message)
    { return functions->ThrowNew(this, clazz, message); }

    jthrowable ExceptionOccurred()
    { return functions->ExceptionOccurred(this); }

    void ExceptionDescribe()
    { functions->ExceptionDescribe(this); }

    void ExceptionClear()
    { functions->ExceptionClear(this); }

    void FatalError(const char* msg)
    { functions->FatalError(this, msg); }

    jint PushLocalFrame(jint capacity)
    { return functions->PushLocalFrame(this, capacity); }

    jobject PopLocalFrame(jobject result)
    { return functions->PopLocalFrame(this, result); }

    jobject NewGlobalRef(jobject obj)
    { return functions->NewGlobalRef(this, obj); }

    void DeleteGlobalRef(jobject globalRef)
    { functions->DeleteGlobalRef(this, globalRef); }

    void DeleteLocalRef(jobject localRef)
    { functions->DeleteLocalRef(this, localRef); }

    jboolean IsSameObject(jobject ref1, jobject ref2)
    { return functions->IsSameObject(this, ref1, ref2); }

    jobject NewLocalRef(jobject ref)
    { return functions->NewLocalRef(this, ref); }

    jint EnsureLocalCapacity(jint capacity)
    { return functions->EnsureLocalCapacity(this, capacity); }

    jobject AllocObject(jclass clazz)
    { return functions->AllocObject(this, clazz); }

    jobject NewObject(jclass clazz, jmethodID methodID, ...)
    {
        va_list args;
        va_start(args, methodID);
        jobject result = functions->NewObjectV(this, clazz, methodID, args);
        va_end(args);
        return result;
    }

    jobject NewObjectV(jclass clazz, jmethodID methodID, va_list args)
    { return functions->NewObjectV(this, clazz, methodID, args); }

    jobject NewObjectA(jclass clazz, jmethodID methodID, jvalue* args)
    { return functions->NewObjectA(this, clazz, methodID, args); }

    jclass GetObjectClass(jobject obj)
    { return functions->GetObjectClass(this, obj); }

    jboolean IsInstanceOf(jobject obj, jclass clazz)
    { return functions->IsInstanceOf(this, obj, clazz); }

    jmethodID GetMethodID(jclass clazz, const char* name, const char* sig)
    { return functions->GetMethodID(this, clazz, name, sig); }

#define CALL_TYPE_METHOD(_jtype, _jname)                                    \
    _jtype Call##_jname##Method(jobject obj, jmethodID methodID, ...)       \
    {                                                                       \
        _jtype result;                                                      \
        va_list args;                                                       \
        va_start(args, methodID);                                           \
        result = functions->Call##_jname##MethodV(this, obj, methodID,      \
                    args);                                                  \
        va_end(args);                                                       \
        return result;                                                      \
    }
#define CALL_TYPE_METHODV(_jtype, _jname)                                   \
    _jtype Call##_jname##MethodV(jobject obj, jmethodID methodID,           \
        va_list args)                                                       \
    { return functions->Call##_jname##MethodV(this, obj, methodID, args); }
#define CALL_TYPE_METHODA(_jtype, _jname)                                   \
    _jtype Call##_jname##MethodA(jobject obj, jmethodID methodID,           \
        jvalue* args)                                                       \
    { return functions->Call##_jname##MethodA(this, obj, methodID, args); }

#define CALL_TYPE(_jtype, _jname)                                           \
    CALL_TYPE_METHOD(_jtype, _jname)                                        \
    CALL_TYPE_METHODV(_jtype, _jname)                                       \
    CALL_TYPE_METHODA(_jtype, _jname)

    CALL_TYPE(jobject, Object)
    CALL_TYPE(jboolean, Boolean)
    CALL_TYPE(jbyte, Byte)
    CALL_TYPE(jchar, Char)
    CALL_TYPE(jshort, Short)
    CALL_TYPE(jint, Int)
    CALL_TYPE(jlong, Long)
    CALL_TYPE(jfloat, Float)
    CALL_TYPE(jdouble, Double)

    void CallVoidMethod(jobject obj, jmethodID methodID, ...)
    {
        va_list args;
        va_start(args, methodID);
        functions->CallVoidMethodV(this, obj, methodID, args);
        va_end(args);
    }

.

.

.

省略一部分

#if defined(__cplusplus)
typedef _JNIEnv JNIEnv;
typedef _JavaVM JavaVM;
#else
typedef const struct JNINativeInterface* JNIEnv;
typedef const struct JNIInvokeInterface* JavaVM;
#endif

/*
 * Table of interface function pointers.
 */
struct JNINativeInterface {
    void*       reserved0;
    void*       reserved1;
    void*       reserved2;
    void*       reserved3;

    jint        (*GetVersion)(JNIEnv *);

    jclass      (*DefineClass)(JNIEnv*, const char*, jobject, const jbyte*,
                        jsize);
    jclass      (*FindClass)(JNIEnv*, const char*);

    jmethodID   (*FromReflectedMethod)(JNIEnv*, jobject);
    jfieldID    (*FromReflectedField)(JNIEnv*, jobject);
    /* spec doesn't show jboolean parameter */
    jobject     (*ToReflectedMethod)(JNIEnv*, jclass, jmethodID, jboolean);

    jclass      (*GetSuperclass)(JNIEnv*, jclass);
    jboolean    (*IsAssignableFrom)(JNIEnv*, jclass, jclass);

    /* spec doesn't show jboolean parameter */
    jobject     (*ToReflectedField)(JNIEnv*, jclass, jfieldID, jboolean);

    jint        (*Throw)(JNIEnv*, jthrowable);
    jint        (*ThrowNew)(JNIEnv *, jclass, const char *);
    jthrowable  (*ExceptionOccurred)(JNIEnv*);
    void        (*ExceptionDescribe)(JNIEnv*);
    void        (*ExceptionClear)(JNIEnv*);
    void        (*FatalError)(JNIEnv*, const char*);

    jint        (*PushLocalFrame)(JNIEnv*, jint);
    jobject     (*PopLocalFrame)(JNIEnv*, jobject);

    jobject     (*NewGlobalRef)(JNIEnv*, jobject);
    void        (*DeleteGlobalRef)(JNIEnv*, jobject);
    void        (*DeleteLocalRef)(JNIEnv*, jobject);
    jboolean    (*IsSameObject)(JNIEnv*, jobject, jobject);

    jobject     (*NewLocalRef)(JNIEnv*, jobject);
    jint        (*EnsureLocalCapacity)(JNIEnv*, jint);

    jobject     (*AllocObject)(JNIEnv*, jclass);
    jobject     (*NewObject)(JNIEnv*, jclass, jmethodID, ...);
    jobject     (*NewObjectV)(JNIEnv*, jclass, jmethodID, va_list);
    jobject     (*NewObjectA)(JNIEnv*, jclass, jmethodID, jvalue*);

    jclass      (*GetObjectClass)(JNIEnv*, jobject);
    jboolean    (*IsInstanceOf)(JNIEnv*, jobject, jclass);
    jmethodID   (*GetMethodID)(JNIEnv*, jclass, const char*, const char*);

    jobject     (*CallObjectMethod)(JNIEnv*, jobject, jmethodID, ...);
    jobject     (*CallObjectMethodV)(JNIEnv*, jobject, jmethodID, va_list);
    jobject     (*CallObjectMethodA)(JNIEnv*, jobject, jmethodID, jvalue*);
    jboolean    (*CallBooleanMethod)(JNIEnv*, jobject, jmethodID, ...);
    jboolean    (*CallBooleanMethodV)(JNIEnv*, jobject, jmethodID, va_list);
    jboolean    (*CallBooleanMethodA)(JNIEnv*, jobject, jmethodID, jvalue*);
    jbyte       (*CallByteMethod)(JNIEnv*, jobject, jmethodID, ...);
    jbyte       (*CallByteMethodV)(JNIEnv*, jobject, jmethodID, va_list);
    jbyte       (*CallByteMethodA)(JNIEnv*, jobject, jmethodID, jvalue*);
    jchar       (*CallCharMethod)(JNIEnv*, jobject, jmethodID, ...);
    jchar       (*CallCharMethodV)(JNIEnv*, jobject, jmethodID, va_list);
    jchar       (*CallCharMethodA)(JNIEnv*, jobject, jmethodID, jvalue*);
    jshort      (*CallShortMethod)(JNIEnv*, jobject, jmethodID, ...);
    jshort      (*CallShortMethodV)(JNIEnv*, jobject, jmethodID, va_list);
    jshort      (*CallShortMethodA)(JNIEnv*, jobject, jmethodID, jvalue*);
    jint        (*CallIntMethod)(JNIEnv*, jobject, jmethodID, ...);
    jint        (*CallIntMethodV)(JNIEnv*, jobject, jmethodID, va_list);
    jint        (*CallIntMethodA)(JNIEnv*, jobject, jmethodID, jvalue*);
    jlong       (*CallLongMethod)(JNIEnv*, jobject, jmethodID, ...);
    jlong       (*CallLongMethodV)(JNIEnv*, jobject, jmethodID, va_list);
    jlong       (*CallLongMethodA)(JNIEnv*, jobject, jmethodID, jvalue*);
    jfloat      (*CallFloatMethod)(JNIEnv*, jobject, jmethodID, ...);
    jfloat      (*CallFloatMethodV)(JNIEnv*, jobject, jmethodID, va_list);
    jfloat      (*CallFloatMethodA)(JNIEnv*, jobject, jmethodID, jvalue*);
    jdouble     (*CallDoubleMethod)(JNIEnv*, jobject, jmethodID, ...);
    jdouble     (*CallDoubleMethodV)(JNIEnv*, jobject, jmethodID, va_list);
    jdouble     (*CallDoubleMethodA)(JNIEnv*, jobject, jmethodID, jvalue*);
    void        (*CallVoidMethod)(JNIEnv*, jobject, jmethodID, ...);
    void        (*CallVoidMethodV)(JNIEnv*, jobject, jmethodID, va_list);
    void        (*CallVoidMethodA)(JNIEnv*, jobject, jmethodID, jvalue*);

android_source_code_dir\dalvik\vm\Jni.cpp

/*
 * Dalvik implementation of JNI interfaces.
 */
#include "Dalvik.h"
#include "JniInternal.h"
#include "ScopedPthreadMutexLock.h"
#include "UniquePtr.h"

#include <stdlib.h>
#include <stdarg.h>
#include <limits.h>
/*
 * ===========================================================================
 *      JNI implementation
 * ===========================================================================
 */

/*
 * Return the version of the native method interface.
 */
static jint GetVersion(JNIEnv* env) {
    /*
     * There is absolutely no need to toggle the mode for correct behavior.
     * However, it does provide native code with a simple "suspend self
     * if necessary" call.
     */
    ScopedJniThreadState ts(env);
    return JNI_VERSION_1_6;
}

/*
 * Create a new class from a bag of bytes.
 *
 * This is not currently supported within Dalvik.
 */
static jclass DefineClass(JNIEnv* env, const char *name, jobject loader,
    const jbyte* buf, jsize bufLen)
{
    UNUSED_PARAMETER(name);
    UNUSED_PARAMETER(loader);
    UNUSED_PARAMETER(buf);
    UNUSED_PARAMETER(bufLen);

    ScopedJniThreadState ts(env);
    LOGW("JNI DefineClass is not supported");
    return NULL;
}

/*
 * Find a class by name.
 *
 * We have to use the "no init" version of FindClass here, because we might
 * be getting the class prior to registering native methods that will be
 * used in <clinit>.
 *
 * We need to get the class loader associated with the current native
 * method.  If there is no native method, e.g. we're calling this from native
 * code right after creating the VM, the spec says we need to use the class
 * loader returned by "ClassLoader.getBaseClassLoader".  There is no such
 * method, but it's likely they meant ClassLoader.getSystemClassLoader.
 * We can't get that until after the VM has initialized though.
 */
static jclass FindClass(JNIEnv* env, const char* name) {
    ScopedJniThreadState ts(env);

    const Method* thisMethod = dvmGetCurrentJNIMethod();
    assert(thisMethod != NULL);

    Object* loader;
    Object* trackedLoader = NULL;
    if (ts.self()->classLoaderOverride != NULL) {
        /* hack for JNI_OnLoad */
        assert(strcmp(thisMethod->name, "nativeLoad") == 0);
        loader = ts.self()->classLoaderOverride;
    } else if (thisMethod == gDvm.methDalvikSystemNativeStart_main ||
               thisMethod == gDvm.methDalvikSystemNativeStart_run) {
        /* start point of invocation interface */
        if (!gDvm.initializing) {
            loader = trackedLoader = dvmGetSystemClassLoader();
        } else {
            loader = NULL;
        }
    } else {
        loader = thisMethod->clazz->classLoader;
    }

    char* descriptor = dvmNameToDescriptor(name);
    if (descriptor == NULL) {
        return NULL;
    }
    ClassObject* clazz = dvmFindClassNoInit(descriptor, loader);
    free(descriptor);

    jclass jclazz = (jclass) addLocalReference(ts.self(), (Object*) clazz);
    dvmReleaseTrackedAlloc(trackedLoader, ts.self());
    return jclazz;
}

/*
 * Return the superclass of a class.
 */
static jclass GetSuperclass(JNIEnv* env, jclass jclazz) {
    ScopedJniThreadState ts(env);
    ClassObject* clazz = (ClassObject*) dvmDecodeIndirectRef(ts.self(), jclazz);
    return (jclass) addLocalReference(ts.self(), (Object*)clazz->super);
}

/*
 * Determine whether an object of clazz1 can be safely cast to clazz2.
 *
 * Like IsInstanceOf, but with a pair of class objects instead of obj+class.
 */
static jboolean IsAssignableFrom(JNIEnv* env, jclass jclazz1, jclass jclazz2) {
    ScopedJniThreadState ts(env);
    ClassObject* clazz1 = (ClassObject*) dvmDecodeIndirectRef(ts.self(), jclazz1);
    ClassObject* clazz2 = (ClassObject*) dvmDecodeIndirectRef(ts.self(), jclazz2);
    return dvmInstanceof(clazz1, clazz2);
}

/*
 * Given a java.lang.reflect.Method or .Constructor, return a methodID.
 */
static jmethodID FromReflectedMethod(JNIEnv* env, jobject jmethod) {
    ScopedJniThreadState ts(env);
    Object* method = dvmDecodeIndirectRef(ts.self(), jmethod);
    return (jmethodID) dvmGetMethodFromReflectObj(method);
}

/*
 * Given a java.lang.reflect.Field, return a fieldID.
 */
static jfieldID FromReflectedField(JNIEnv* env, jobject jfield) {
    ScopedJniThreadState ts(env);
    Object* field = dvmDecodeIndirectRef(ts.self(), jfield);
    return (jfieldID) dvmGetFieldFromReflectObj(field);
}

其它省略