探索Android中的Parcel机制（上）

一．先从Serialize说起

我们都知道JAVA中的Serialize机制，译成串行化、序列化……，其作用是能将数据对象存入字节流其中，在须要时又一次生成对象。主要应用是利用外部存储设备保存对象状态，以及通过网络传输对象等。

二．Android中的新的序列化机制

在Android系统中，定位为针对内存受限的设备，因此对性能要求更高，另外系统中採用了新的IPC（进程间通信）机制，必定要求使用性能更出色的对象传输方式。在这种环境下，Parcel被设计出来，其定位就是轻量级的高效的对象序列化和反序列化机制。

三．Parcel类的背后

在Framework中有parcel类，源代码路径是：

Frameworks/base/core/java/android/os/Parcel.java

典型的源代码片断例如以下：

/**
* Write an integer value into the parcel at the current dataPosition(),
* growing dataCapacity() if needed.
*/
public final native void writeInt(int val);

/**
* Write a long integer value into the parcel at the current dataPosition(),
* growing dataCapacity() if needed.
*/
public final native void writeLong(long val);

从中我们看到，从这个源程序文件里我们看不到真正的功能是怎样实现的，必须透过JNI往下走了。于是，Frameworks/base/core/jni/android_util_Binder.cpp中找到了线索

static void android_os_Parcel_writeInt(JNIEnv* env, jobject clazz, jint val)
{
Parcel* parcel = parcelForJavaObject(env, clazz);
if (parcel != NULL) {
const status_t err = parcel->writeInt32(val);
if (err != NO_ERROR) {
jniThrowException(env, "java/lang/OutOfMemoryError", NULL);
}
}
}

static void android_os_Parcel_writeLong(JNIEnv* env, jobject clazz, jlong val)
{
Parcel* parcel = parcelForJavaObject(env, clazz);
if (parcel != NULL) {
const status_t err = parcel->writeInt64(val);
if (err != NO_ERROR) {
jniThrowException(env, "java/lang/OutOfMemoryError", NULL);
}
}
}

从这里我们能够得到的信息是函数的实现依赖于Parcel指针，因此还须要找到Parcel的类定义，注意，这里的类已经是用C++语言实现的了。

找到Frameworks/base/include/binder/parcel.h和Frameworks/base/libs/binder/parcel.cpp。最终找到了最终的实现代码了。

有兴趣的朋友能够自己读一下，不难理解，这里把主要的思路总结一下：

1.       整个读写全是在内存中进行，主要是通过malloc()、realloc()、memcpy()等内存操作进行，所以效率比JAVA序列化中使用外部存储器会高非常多；

2.       读写时是4字节对齐的，能够看到#define PAD_SIZE(s) (((s)+3)&~3)这句宏定义就是在做这件事情；

3.       假设预分配的空间不够时newSize = ((mDataSize+len)*3)/2;会一次多分配50%；

4.       对于普通数据，使用的是mData内存地址，对于IBinder类型的数据以及FileDescriptor使用的是mObjects内存地址。后者是通过flatten_binder()和unflatten_binder()实现的，目的是反序列化时读出的对象就是原对象而不用又一次new一个新对象。

好了，这就是Parcel背后的动作，全是在一块内存里进行读写操作，就不啰嗦了，把parcel的代码贴在这供没有源代码的朋友參考吧。接下来我会用一个小DEMO演示一下Parcel类在应用程序中的使用，详见《探索Android中的Parcel机制（下）》。

/*
* Copyright (C) 2005 The Android Open Source Project
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/

#ifndef ANDROID_PARCEL_H
#define ANDROID_PARCEL_H

#include <cutils/native_handle.h>
#include <utils/Errors.h>
#include <utils/RefBase.h>
#include <utils/String16.h>
#include <utils/Vector.h>

// ---------------------------------------------------------------------------
namespace android {

class IBinder;
class ProcessState;
class String8;
class TextOutput;
class Flattenable;

struct flat_binder_object; // defined in support_p/binder_module.h

class Parcel
{
public:
Parcel();
~Parcel();

const uint8_t* data() const;
size_t dataSize() const;
size_t dataAvail() const;
size_t dataPosition() const;
size_t dataCapacity() const;

status_t setDataSize(size_t size);
void setDataPosition(size_t pos) const;
status_t setDataCapacity(size_t size);

status_t setData(const uint8_t* buffer, size_t len);

status_t appendFrom(Parcel *parcel, size_t start, size_t len);

bool hasFileDescriptors() const;

status_t writeInterfaceToken(const String16& interface);
bool enforceInterface(const String16& interface) const;
bool checkInterface(IBinder*) const;

void freeData();

const size_t* objects() const;
size_t objectsCount() const;

status_t errorCheck() const;
void setError(status_t err);

status_t write(const void* data, size_t len);
void* writeInplace(size_t len);
status_t writeUnpadded(const void* data, size_t len);
status_t writeInt32(int32_t val);
status_t writeInt64(int64_t val);
status_t writeFloat(float val);
status_t writeDouble(double val);
status_t writeIntPtr(intptr_t val);
status_t writeCString(const char* str);
status_t writeString8(const String8& str);
status_t writeString16(const String16& str);
status_t writeString16(const char16_t* str, size_t len);
status_t writeStrongBinder(const sp<IBinder>& val);
status_t writeWeakBinder(const wp<IBinder>& val);
status_t write(const Flattenable& val);

// Place a native_handle into the parcel (the native_handle's file-
// descriptors are dup'ed, so it is safe to delete the native_handle
// when this function returns).
// Doesn't take ownership of the native_handle.
status_t writeNativeHandle(const native_handle* handle);

// Place a file descriptor into the parcel. The given fd must remain
// valid for the lifetime of the parcel.
status_t writeFileDescriptor(int fd);

// Place a file descriptor into the parcel. A dup of the fd is made, which
// will be closed once the parcel is destroyed.
status_t writeDupFileDescriptor(int fd);

status_t writeObject(const flat_binder_object& val, bool nullMetaData);

void remove(size_t start, size_t amt);

status_t read(void* outData, size_t len) const;
const void* readInplace(size_t len) const;
int32_t readInt32() const;
status_t readInt32(int32_t *pArg) const;
int64_t readInt64() const;
status_t readInt64(int64_t *pArg) const;
float readFloat() const;
status_t readFloat(float *pArg) const;
double readDouble() const;
status_t readDouble(double *pArg) const;
intptr_t readIntPtr() const;
status_t readIntPtr(intptr_t *pArg) const;

const char* readCString() const;
String8 readString8() const;
String16 readString16() const;
const char16_t* readString16Inplace(size_t* outLen) const;
sp<IBinder> readStrongBinder() const;
wp<IBinder> readWeakBinder() const;
status_t read(Flattenable& val) const;

// Retrieve native_handle from the parcel. This returns a copy of the
// parcel's native_handle (the caller takes ownership). The caller
// must free the native_handle with native_handle_close() and
// native_handle_delete().
native_handle* readNativeHandle() const;

// Retrieve a file descriptor from the parcel. This returns the raw fd
// in the parcel, which you do not own -- use dup() to get your own copy.
int readFileDescriptor() const;

const flat_binder_object* readObject(bool nullMetaData) const;

// Explicitly close all file descriptors in the parcel.
void closeFileDescriptors();

typedef void (*release_func)(Parcel* parcel,
const uint8_t* data, size_t dataSize,
const size_t* objects, size_t objectsSize,
void* cookie);

const uint8_t* ipcData() const;
size_t ipcDataSize() const;
const size_t* ipcObjects() const;
size_t ipcObjectsCount() const;
void ipcSetDataReference(const uint8_t* data, size_t dataSize,
const size_t* objects, size_t objectsCount,
release_func relFunc, void* relCookie);

void print(TextOutput& to, uint32_t flags = 0) const;

private:
Parcel(const Parcel& o);
Parcel& operator=(const Parcel& o);

status_t finishWrite(size_t len);
void releaseObjects();
void acquireObjects();
status_t growData(size_t len);
status_t restartWrite(size_t desired);
status_t continueWrite(size_t desired);
void freeDataNoInit();
void initState();
void scanForFds() const;

template<class T>
status_t readAligned(T *pArg) const;

template<class T> T readAligned() const;

template<class T>
status_t writeAligned(T val);

status_t mError;
uint8_t* mData;
size_t mDataSize;
size_t mDataCapacity;
mutable size_t mDataPos;
size_t* mObjects;
size_t mObjectsSize;
size_t mObjectsCapacity;
mutable size_t mNextObjectHint;

mutable bool mFdsKnown;
mutable bool mHasFds;

release_func mOwner;
void* mOwnerCookie;
};

// ---------------------------------------------------------------------------

inline TextOutput& operator<<(TextOutput& to, const Parcel& parcel)
{
parcel.print(to);
return to;
}

// ---------------------------------------------------------------------------

// Generic acquire and release of objects.
void acquire_object(const sp<ProcessState>& proc,
const flat_binder_object& obj, const void* who);
void release_object(const sp<ProcessState>& proc,
const flat_binder_object& obj, const void* who);

void flatten_binder(const sp<ProcessState>& proc,
const sp<IBinder>& binder, flat_binder_object* out);
void flatten_binder(const sp<ProcessState>& proc,
const wp<IBinder>& binder, flat_binder_object* out);
status_t unflatten_binder(const sp<ProcessState>& proc,
const flat_binder_object& flat, sp<IBinder>* out);
status_t unflatten_binder(const sp<ProcessState>& proc,
const flat_binder_object& flat, wp<IBinder>* out);

}; // namespace android

// ---------------------------------------------------------------------------

#endif // ANDROID_PARCEL_H

/*
* Copyright (C) 2005 The Android Open Source Project
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/

#define LOG_TAG "Parcel"
//#define LOG_NDEBUG 0

#include <binder/Parcel.h>

#include <binder/Binder.h>
#include <binder/BpBinder.h>
#include <utils/Debug.h>
#include <binder/ProcessState.h>
#include <utils/Log.h>
#include <utils/String8.h>
#include <utils/String16.h>
#include <utils/TextOutput.h>
#include <utils/misc.h>
#include <utils/Flattenable.h>

#include <private/binder/binder_module.h>

#include <stdio.h>
#include <stdlib.h>
#include <stdint.h>

#ifndef INT32_MAX
#define INT32_MAX ((int32_t)(2147483647))
#endif

#define LOG_REFS(...)
//#define LOG_REFS(...) LOG(LOG_DEBUG, "Parcel", __VA_ARGS__)

// ---------------------------------------------------------------------------

#define PAD_SIZE(s) (((s)+3)&~3)

// XXX This can be made public if we want to provide
// support for typed data.
struct small_flat_data
{
uint32_t type;
uint32_t data;
};

namespace android {

void acquire_object(const sp<ProcessState>& proc,
const flat_binder_object& obj, const void* who)
{
switch (obj.type) {
case BINDER_TYPE_BINDER:
if (obj.binder) {
LOG_REFS("Parcel %p acquiring reference on local %p", who, obj.cookie);
static_cast<IBinder*>(obj.cookie)->incStrong(who);
}
return;
case BINDER_TYPE_WEAK_BINDER:
if (obj.binder)
static_cast<RefBase::weakref_type*>(obj.binder)->incWeak(who);
return;
case BINDER_TYPE_HANDLE: {
const sp<IBinder> b = proc->getStrongProxyForHandle(obj.handle);
if (b != NULL) {
LOG_REFS("Parcel %p acquiring reference on remote %p", who, b.get());
b->incStrong(who);
}
return;
}
case BINDER_TYPE_WEAK_HANDLE: {
const wp<IBinder> b = proc->getWeakProxyForHandle(obj.handle);
if (b != NULL) b.get_refs()->incWeak(who);
return;
}
case BINDER_TYPE_FD: {
// intentionally blank -- nothing to do to acquire this, but we do
// recognize it as a legitimate object type.
return;
}
}

LOGD("Invalid object type 0x%08lx", obj.type);
}

void release_object(const sp<ProcessState>& proc,
const flat_binder_object& obj, const void* who)
{
switch (obj.type) {
case BINDER_TYPE_BINDER:
if (obj.binder) {
LOG_REFS("Parcel %p releasing reference on local %p", who, obj.cookie);
static_cast<IBinder*>(obj.cookie)->decStrong(who);
}
return;
case BINDER_TYPE_WEAK_BINDER:
if (obj.binder)
static_cast<RefBase::weakref_type*>(obj.binder)->decWeak(who);
return;
case BINDER_TYPE_HANDLE: {
const sp<IBinder> b = proc->getStrongProxyForHandle(obj.handle);
if (b != NULL) {
LOG_REFS("Parcel %p releasing reference on remote %p", who, b.get());
b->decStrong(who);
}
return;
}
case BINDER_TYPE_WEAK_HANDLE: {
const wp<IBinder> b = proc->getWeakProxyForHandle(obj.handle);
if (b != NULL) b.get_refs()->decWeak(who);
return;
}
case BINDER_TYPE_FD: {
if (obj.cookie != (void*)0) close(obj.handle);
return;
}
}

LOGE("Invalid object type 0x%08lx", obj.type);
}

inline static status_t finish_flatten_binder(
const sp<IBinder>& binder, const flat_binder_object& flat, Parcel* out)
{
return out->writeObject(flat, false);
}

status_t flatten_binder(const sp<ProcessState>& proc,
const sp<IBinder>& binder, Parcel* out)
{
flat_binder_object obj;

obj.flags = 0x7f | FLAT_BINDER_FLAG_ACCEPTS_FDS;
if (binder != NULL) {
IBinder *local = binder->localBinder();
if (!local) {
BpBinder *proxy = binder->remoteBinder();
if (proxy == NULL) {
LOGE("null proxy");
}
const int32_t handle = proxy ? proxy->handle() : 0;
obj.type = BINDER_TYPE_HANDLE;
obj.handle = handle;
obj.cookie = NULL;
} else {
obj.type = BINDER_TYPE_BINDER;
obj.binder = local->getWeakRefs();
obj.cookie = local;
}
} else {
obj.type = BINDER_TYPE_BINDER;
obj.binder = NULL;
obj.cookie = NULL;
}

return finish_flatten_binder(binder, obj, out);
}

status_t flatten_binder(const sp<ProcessState>& proc,
const wp<IBinder>& binder, Parcel* out)
{
flat_binder_object obj;

obj.flags = 0x7f | FLAT_BINDER_FLAG_ACCEPTS_FDS;
if (binder != NULL) {
sp<IBinder> real = binder.promote();
if (real != NULL) {
IBinder *local = real->localBinder();
if (!local) {
BpBinder *proxy = real->remoteBinder();
if (proxy == NULL) {
LOGE("null proxy");
}
const int32_t handle = proxy ? proxy->handle() : 0;
obj.type = BINDER_TYPE_WEAK_HANDLE;
obj.handle = handle;
obj.cookie = NULL;
} else {
obj.type = BINDER_TYPE_WEAK_BINDER;
obj.binder = binder.get_refs();
obj.cookie = binder.unsafe_get();
}
return finish_flatten_binder(real, obj, out);
}

// XXX How to deal? In order to flatten the given binder,
// we need to probe it for information, which requires a primary
// reference... but we don't have one.
//
// The OpenBinder implementation uses a dynamic_cast<> here,
// but we can't do that with the different reference counting
// implementation we are using.
LOGE("Unable to unflatten Binder weak reference!");
obj.type = BINDER_TYPE_BINDER;
obj.binder = NULL;
obj.cookie = NULL;
return finish_flatten_binder(NULL, obj, out);

} else {
obj.type = BINDER_TYPE_BINDER;
obj.binder = NULL;
obj.cookie = NULL;
return finish_flatten_binder(NULL, obj, out);
}
}

inline static status_t finish_unflatten_binder(
BpBinder* proxy, const flat_binder_object& flat, const Parcel& in)
{
return NO_ERROR;
}

status_t unflatten_binder(const sp<ProcessState>& proc,
const Parcel& in, sp<IBinder>* out)
{
const flat_binder_object* flat = in.readObject(false);

if (flat) {
switch (flat->type) {
case BINDER_TYPE_BINDER:
*out = static_cast<IBinder*>(flat->cookie);
return finish_unflatten_binder(NULL, *flat, in);
case BINDER_TYPE_HANDLE:
*out = proc->getStrongProxyForHandle(flat->handle);
return finish_unflatten_binder(
static_cast<BpBinder*>(out->get()), *flat, in);
}
}
return BAD_TYPE;
}

status_t unflatten_binder(const sp<ProcessState>& proc,
const Parcel& in, wp<IBinder>* out)
{
const flat_binder_object* flat = in.readObject(false);

if (flat) {
switch (flat->type) {
case BINDER_TYPE_BINDER:
*out = static_cast<IBinder*>(flat->cookie);
return finish_unflatten_binder(NULL, *flat, in);
case BINDER_TYPE_WEAK_BINDER:
if (flat->binder != NULL) {
out->set_object_and_refs(
static_cast<IBinder*>(flat->cookie),
static_cast<RefBase::weakref_type*>(flat->binder));
} else {
*out = NULL;
}
return finish_unflatten_binder(NULL, *flat, in);
case BINDER_TYPE_HANDLE:
case BINDER_TYPE_WEAK_HANDLE:
*out = proc->getWeakProxyForHandle(flat->handle);
return finish_unflatten_binder(
static_cast<BpBinder*>(out->unsafe_get()), *flat, in);
}
}
return BAD_TYPE;
}

// ---------------------------------------------------------------------------

Parcel::Parcel()
{
initState();
}

Parcel::~Parcel()
{
freeDataNoInit();
}

const uint8_t* Parcel::data() const
{
return mData;
}

size_t Parcel::dataSize() const
{
return (mDataSize > mDataPos ? mDataSize : mDataPos);
}

size_t Parcel::dataAvail() const
{
// TODO: decide what to do about the possibility that this can
// report an available-data size that exceeds a Java int's max
// positive value, causing havoc. Fortunately this will only
// happen if someone constructs a Parcel containing more than two
// gigabytes of data, which on typical phone hardware is simply
// not possible.
return dataSize() - dataPosition();
}

size_t Parcel::dataPosition() const
{
return mDataPos;
}

size_t Parcel::dataCapacity() const
{
return mDataCapacity;
}

status_t Parcel::setDataSize(size_t size)
{
status_t err;
err = continueWrite(size);
if (err == NO_ERROR) {
mDataSize = size;
LOGV("setDataSize Setting data size of %p to %d/n", this, mDataSize);
}
return err;
}

void Parcel::setDataPosition(size_t pos) const
{
mDataPos = pos;
mNextObjectHint = 0;
}

status_t Parcel::setDataCapacity(size_t size)
{
if (size > mDataSize) return continueWrite(size);
return NO_ERROR;
}

status_t Parcel::setData(const uint8_t* buffer, size_t len)
{
status_t err = restartWrite(len);
if (err == NO_ERROR) {
memcpy(const_cast<uint8_t*>(data()), buffer, len);
mDataSize = len;
mFdsKnown = false;
}
return err;
}

status_t Parcel::appendFrom(Parcel *parcel, size_t offset, size_t len)
{
const sp<ProcessState> proc(ProcessState::self());
status_t err;
uint8_t *data = parcel->mData;
size_t *objects = parcel->mObjects;
size_t size = parcel->mObjectsSize;
int startPos = mDataPos;
int firstIndex = -1, lastIndex = -2;

if (len == 0) {
return NO_ERROR;
}

// range checks against the source parcel size
if ((offset > parcel->mDataSize)
|| (len > parcel->mDataSize)
|| (offset + len > parcel->mDataSize)) {
return BAD_VALUE;
}

// Count objects in range
for (int i = 0; i < (int) size; i++) {
size_t off = objects[i];
if ((off >= offset) && (off < offset + len)) {
if (firstIndex == -1) {
firstIndex = i;
}
lastIndex = i;
}
}
int numObjects = lastIndex - firstIndex + 1;

// grow data
err = growData(len);
if (err != NO_ERROR) {
return err;
}

// append data
memcpy(mData + mDataPos, data + offset, len);
mDataPos += len;
mDataSize += len;

if (numObjects > 0) {
// grow objects
if (mObjectsCapacity < mObjectsSize + numObjects) {
int newSize = ((mObjectsSize + numObjects)*3)/2;
size_t *objects =
(size_t*)realloc(mObjects, newSize*sizeof(size_t));
if (objects == (size_t*)0) {
return NO_MEMORY;
}
mObjects = objects;
mObjectsCapacity = newSize;
}

// append and acquire objects
int idx = mObjectsSize;
for (int i = firstIndex; i <= lastIndex; i++) {
size_t off = objects[i] - offset + startPos;
mObjects[idx++] = off;
mObjectsSize++;

flat_binder_object* flat
= reinterpret_cast<flat_binder_object*>(mData + off);
acquire_object(proc, *flat, this);

if (flat->type == BINDER_TYPE_FD) {
// If this is a file descriptor, we need to dup it so the
// new Parcel now owns its own fd, and can declare that we
// officially know we have fds.
flat->handle = dup(flat->handle);
flat->cookie = (void*)1;
mHasFds = mFdsKnown = true;
}
}
}

return NO_ERROR;
}

bool Parcel::hasFileDescriptors() const
{
if (!mFdsKnown) {
scanForFds();
}
return mHasFds;
}

status_t Parcel::writeInterfaceToken(const String16& interface)
{
// currently the interface identification token is just its name as a string
return writeString16(interface);
}

bool Parcel::checkInterface(IBinder* binder) const
{
return enforceInterface(binder->getInterfaceDescriptor());
}

bool Parcel::enforceInterface(const String16& interface) const
{
const String16 str(readString16());
if (str == interface) {
return true;
} else {
LOGW("**** enforceInterface() expected '%s' but read '%s'/n",
String8(interface).string(), String8(str).string());
return false;
}
}

const size_t* Parcel::objects() const
{
return mObjects;
}

size_t Parcel::objectsCount() const
{
return mObjectsSize;
}

status_t Parcel::errorCheck() const
{
return mError;
}

void Parcel::setError(status_t err)
{
mError = err;
}

status_t Parcel::finishWrite(size_t len)
{
//printf("Finish write of %d/n", len);
mDataPos += len;
LOGV("finishWrite Setting data pos of %p to %d/n", this, mDataPos);
if (mDataPos > mDataSize) {
mDataSize = mDataPos;
LOGV("finishWrite Setting data size of %p to %d/n", this, mDataSize);
}
//printf("New pos=%d, size=%d/n", mDataPos, mDataSize);
return NO_ERROR;
}

status_t Parcel::writeUnpadded(const void* data, size_t len)
{
size_t end = mDataPos + len;
if (end < mDataPos) {
// integer overflow
return BAD_VALUE;
}

if (end <= mDataCapacity) {
restart_write:
memcpy(mData+mDataPos, data, len);
return finishWrite(len);
}

status_t err = growData(len);
if (err == NO_ERROR) goto restart_write;
return err;
}

status_t Parcel::write(const void* data, size_t len)
{
void* const d = writeInplace(len);
if (d) {
memcpy(d, data, len);
return NO_ERROR;
}
return mError;
}

void* Parcel::writeInplace(size_t len)
{
const size_t padded = PAD_SIZE(len);

// sanity check for integer overflow
if (mDataPos+padded < mDataPos) {
return NULL;
}

if ((mDataPos+padded) <= mDataCapacity) {
restart_write:
//printf("Writing %ld bytes, padded to %ld/n", len, padded);
uint8_t* const data = mData+mDataPos;

// Need to pad at end?
if (padded != len) {
#if BYTE_ORDER == BIG_ENDIAN
static const uint32_t mask[4] = {
0x00000000, 0xffffff00, 0xffff0000, 0xff000000
};
#endif
#if BYTE_ORDER == LITTLE_ENDIAN
static const uint32_t mask[4] = {
0x00000000, 0x00ffffff, 0x0000ffff, 0x000000ff
};
#endif
//printf("Applying pad mask: %p to %p/n", (void*)mask[padded-len],
// *reinterpret_cast<void**>(data+padded-4));
*reinterpret_cast<uint32_t*>(data+padded-4) &= mask[padded-len];
}

finishWrite(padded);
return data;
}

status_t err = growData(padded);
if (err == NO_ERROR) goto restart_write;
return NULL;
}

status_t Parcel::writeInt32(int32_t val)
{
return writeAligned(val);
}

status_t Parcel::writeInt64(int64_t val)
{
return writeAligned(val);
}

status_t Parcel::writeFloat(float val)
{
return writeAligned(val);
}

status_t Parcel::writeDouble(double val)
{
return writeAligned(val);
}

status_t Parcel::writeIntPtr(intptr_t val)
{
return writeAligned(val);
}

status_t Parcel::writeCString(const char* str)
{
return write(str, strlen(str)+1);
}

status_t Parcel::writeString8(const String8& str)
{
status_t err = writeInt32(str.bytes());
if (err == NO_ERROR) {
err = write(str.string(), str.bytes()+1);
}
return err;
}

status_t Parcel::writeString16(const String16& str)
{
return writeString16(str.string(), str.size());
}

status_t Parcel::writeString16(const char16_t* str, size_t len)
{
if (str == NULL) return writeInt32(-1);

status_t err = writeInt32(len);
if (err == NO_ERROR) {
len *= sizeof(char16_t);
uint8_t* data = (uint8_t*)writeInplace(len+sizeof(char16_t));
if (data) {
memcpy(data, str, len);
*reinterpret_cast<char16_t*>(data+len) = 0;
return NO_ERROR;
}
err = mError;
}
return err;
}

status_t Parcel::writeStrongBinder(const sp<IBinder>& val)
{
return flatten_binder(ProcessState::self(), val, this);
}

status_t Parcel::writeWeakBinder(const wp<IBinder>& val)
{
return flatten_binder(ProcessState::self(), val, this);
}

status_t Parcel::writeNativeHandle(const native_handle* handle)
{
if (!handle || handle->version != sizeof(native_handle))
return BAD_TYPE;

status_t err;
err = writeInt32(handle->numFds);
if (err != NO_ERROR) return err;

err = writeInt32(handle->numInts);
if (err != NO_ERROR) return err;

for (int i=0 ; err==NO_ERROR && i<handle->numFds ; i++)
err = writeDupFileDescriptor(handle->data[i]);

if (err != NO_ERROR) {
LOGD("write native handle, write dup fd failed");
return err;
}
err = write(handle->data + handle->numFds, sizeof(int)*handle->numInts);
return err;
}

status_t Parcel::writeFileDescriptor(int fd)
{
flat_binder_object obj;
obj.type = BINDER_TYPE_FD;
obj.flags = 0x7f | FLAT_BINDER_FLAG_ACCEPTS_FDS;
obj.handle = fd;
obj.cookie = (void*)0;
return writeObject(obj, true);
}

status_t Parcel::writeDupFileDescriptor(int fd)
{
flat_binder_object obj;
obj.type = BINDER_TYPE_FD;
obj.flags = 0x7f | FLAT_BINDER_FLAG_ACCEPTS_FDS;
obj.handle = dup(fd);
obj.cookie = (void*)1;
return writeObject(obj, true);
}

status_t Parcel::write(const Flattenable& val)
{
status_t err;

// size if needed
size_t len = val.getFlattenedSize();
size_t fd_count = val.getFdCount();

err = this->writeInt32(len);
if (err) return err;

err = this->writeInt32(fd_count);
if (err) return err;

// payload
void* buf = this->writeInplace(PAD_SIZE(len));
if (buf == NULL)
return BAD_VALUE;

int* fds = NULL;
if (fd_count) {
fds = new int[fd_count];
}

err = val.flatten(buf, len, fds, fd_count);
for (size_t i=0 ; i<fd_count && err==NO_ERROR ; i++) {
err = this->writeDupFileDescriptor( fds[i] );
}

if (fd_count) {
delete [] fds;
}

return err;
}

status_t Parcel::writeObject(const flat_binder_object& val, bool nullMetaData)
{
const bool enoughData = (mDataPos+sizeof(val)) <= mDataCapacity;
const bool enoughObjects = mObjectsSize < mObjectsCapacity;
if (enoughData && enoughObjects) {
restart_write:
*reinterpret_cast<flat_binder_object*>(mData+mDataPos) = val;

// Need to write meta-data?
if (nullMetaData || val.binder != NULL) {
mObjects[mObjectsSize] = mDataPos;
acquire_object(ProcessState::self(), val, this);
mObjectsSize++;
}

// remember if it's a file descriptor
if (val.type == BINDER_TYPE_FD) {
mHasFds = mFdsKnown = true;
}

return finishWrite(sizeof(flat_binder_object));
}

if (!enoughData) {
const status_t err = growData(sizeof(val));
if (err != NO_ERROR) return err;
}
if (!enoughObjects) {
size_t newSize = ((mObjectsSize+2)*3)/2;
size_t* objects = (size_t*)realloc(mObjects, newSize*sizeof(size_t));
if (objects == NULL) return NO_MEMORY;
mObjects = objects;
mObjectsCapacity = newSize;
}

goto restart_write;
}

void Parcel::remove(size_t start, size_t amt)
{
LOG_ALWAYS_FATAL("Parcel::remove() not yet implemented!");
}

status_t Parcel::read(void* outData, size_t len) const
{
if ((mDataPos+PAD_SIZE(len)) >= mDataPos && (mDataPos+PAD_SIZE(len)) <= mDataSize) {
memcpy(outData, mData+mDataPos, len);
mDataPos += PAD_SIZE(len);
LOGV("read Setting data pos of %p to %d/n", this, mDataPos);
return NO_ERROR;
}
return NOT_ENOUGH_DATA;
}

const void* Parcel::readInplace(size_t len) const
{
if ((mDataPos+PAD_SIZE(len)) >= mDataPos && (mDataPos+PAD_SIZE(len)) <= mDataSize) {
const void* data = mData+mDataPos;
mDataPos += PAD_SIZE(len);
LOGV("readInplace Setting data pos of %p to %d/n", this, mDataPos);
return data;
}
return NULL;
}

template<class T>
status_t Parcel::readAligned(T *pArg) const {
COMPILE_TIME_ASSERT_FUNCTION_SCOPE(PAD_SIZE(sizeof(T)) == sizeof(T));

if ((mDataPos+sizeof(T)) <= mDataSize) {
const void* data = mData+mDataPos;
mDataPos += sizeof(T);
*pArg = *reinterpret_cast<const T*>(data);
return NO_ERROR;
} else {
return NOT_ENOUGH_DATA;
}
}

template<class T>
T Parcel::readAligned() const {
T result;
if (readAligned(&result) != NO_ERROR) {
result = 0;
}

return result;
}

template<class T>
status_t Parcel::writeAligned(T val) {
COMPILE_TIME_ASSERT_FUNCTION_SCOPE(PAD_SIZE(sizeof(T)) == sizeof(T));

if ((mDataPos+sizeof(val)) <= mDataCapacity) {
restart_write:
*reinterpret_cast<T*>(mData+mDataPos) = val;
return finishWrite(sizeof(val));
}

status_t err = growData(sizeof(val));
if (err == NO_ERROR) goto restart_write;
return err;
}

status_t Parcel::readInt32(int32_t *pArg) const
{
return readAligned(pArg);
}

int32_t Parcel::readInt32() const
{
return readAligned<int32_t>();
}

status_t Parcel::readInt64(int64_t *pArg) const
{
return readAligned(pArg);
}

int64_t Parcel::readInt64() const
{
return readAligned<int64_t>();
}

status_t Parcel::readFloat(float *pArg) const
{
return readAligned(pArg);
}

float Parcel::readFloat() const
{
return readAligned<float>();
}

status_t Parcel::readDouble(double *pArg) const
{
return readAligned(pArg);
}

double Parcel::readDouble() const
{
return readAligned<double>();
}

status_t Parcel::readIntPtr(intptr_t *pArg) const
{
return readAligned(pArg);
}

intptr_t Parcel::readIntPtr() const
{
return readAligned<intptr_t>();
}

const char* Parcel::readCString() const
{
const size_t avail = mDataSize-mDataPos;
if (avail > 0) {
const char* str = reinterpret_cast<const char*>(mData+mDataPos);
// is the string's trailing NUL within the parcel's valid bounds?
const char* eos = reinterpret_cast<const char*>(memchr(str, 0, avail));
if (eos) {
const size_t len = eos - str;
mDataPos += PAD_SIZE(len+1);
LOGV("readCString Setting data pos of %p to %d/n", this, mDataPos);
return str;
}
}
return NULL;
}

String8 Parcel::readString8() const
{
int32_t size = readInt32();
// watch for potential int overflow adding 1 for trailing NUL
if (size > 0 && size < INT32_MAX) {
const char* str = (const char*)readInplace(size+1);
if (str) return String8(str, size);
}
return String8();
}

String16 Parcel::readString16() const
{
size_t len;
const char16_t* str = readString16Inplace(&len);
if (str) return String16(str, len);
LOGE("Reading a NULL string not supported here.");
return String16();
}

const char16_t* Parcel::readString16Inplace(size_t* outLen) const
{
int32_t size = readInt32();
// watch for potential int overflow from size+1
if (size >= 0 && size < INT32_MAX) {
*outLen = size;
const char16_t* str = (const char16_t*)readInplace((size+1)*sizeof(char16_t));
if (str != NULL) {
return str;
}
}
*outLen = 0;
return NULL;
}

sp<IBinder> Parcel::readStrongBinder() const
{
sp<IBinder> val;
unflatten_binder(ProcessState::self(), *this, &val);
return val;
}

wp<IBinder> Parcel::readWeakBinder() const
{
wp<IBinder> val;
unflatten_binder(ProcessState::self(), *this, &val);
return val;
}

native_handle* Parcel::readNativeHandle() const
{
int numFds, numInts;
status_t err;
err = readInt32(&numFds);
if (err != NO_ERROR) return 0;
err = readInt32(&numInts);
if (err != NO_ERROR) return 0;

native_handle* h = native_handle_create(numFds, numInts);
for (int i=0 ; err==NO_ERROR && i<numFds ; i++) {
h->data[i] = dup(readFileDescriptor());
if (h->data[i] < 0) err = BAD_VALUE;
}
err = read(h->data + numFds, sizeof(int)*numInts);
if (err != NO_ERROR) {
native_handle_close(h);
native_handle_delete(h);
h = 0;
}
return h;
}

int Parcel::readFileDescriptor() const
{
const flat_binder_object* flat = readObject(true);
if (flat) {
switch (flat->type) {
case BINDER_TYPE_FD:
//LOGI("Returning file descriptor %ld from parcel %p/n", flat->handle, this);
return flat->handle;
}
}
return BAD_TYPE;
}

status_t Parcel::read(Flattenable& val) const
{
// size
const size_t len = this->readInt32();
const size_t fd_count = this->readInt32();

// payload
void const* buf = this->readInplace(PAD_SIZE(len));
if (buf == NULL)
return BAD_VALUE;

int* fds = NULL;
if (fd_count) {
fds = new int[fd_count];
}

status_t err = NO_ERROR;
for (size_t i=0 ; i<fd_count && err==NO_ERROR ; i++) {
fds[i] = dup(this->readFileDescriptor());
if (fds[i] < 0) err = BAD_VALUE;
}

if (err == NO_ERROR) {
err = val.unflatten(buf, len, fds, fd_count);
}

if (fd_count) {
delete [] fds;
}

return err;
}
const flat_binder_object* Parcel::readObject(bool nullMetaData) const
{
const size_t DPOS = mDataPos;
if ((DPOS+sizeof(flat_binder_object)) <= mDataSize) {
const flat_binder_object* obj
= reinterpret_cast<const flat_binder_object*>(mData+DPOS);
mDataPos = DPOS + sizeof(flat_binder_object);
if (!nullMetaData && (obj->cookie == NULL && obj->binder == NULL)) {
// When transferring a NULL object, we don't write it into
// the object list, so we don't want to check for it when
// reading.
LOGV("readObject Setting data pos of %p to %d/n", this, mDataPos);
return obj;
}

// Ensure that this object is valid...
size_t* const OBJS = mObjects;
const size_t N = mObjectsSize;
size_t opos = mNextObjectHint;

if (N > 0) {
LOGV("Parcel %p looking for obj at %d, hint=%d/n",
this, DPOS, opos);

// Start at the current hint position, looking for an object at
// the current data position.
if (opos < N) {
while (opos < (N-1) && OBJS[opos] < DPOS) {
opos++;
}
} else {
opos = N-1;
}
if (OBJS[opos] == DPOS) {
// Found it!
LOGV("Parcel found obj %d at index %d with forward search",
this, DPOS, opos);
mNextObjectHint = opos+1;
LOGV("readObject Setting data pos of %p to %d/n", this, mDataPos);
return obj;
}

// Look backwards for it...
while (opos > 0 && OBJS[opos] > DPOS) {
opos--;
}
if (OBJS[opos] == DPOS) {
// Found it!
LOGV("Parcel found obj %d at index %d with backward search",
this, DPOS, opos);
mNextObjectHint = opos+1;
LOGV("readObject Setting data pos of %p to %d/n", this, mDataPos);
return obj;
}
}
LOGW("Attempt to read object from Parcel %p at offset %d that is not in the object list",
this, DPOS);
}
return NULL;
}

void Parcel::closeFileDescriptors()
{
size_t i = mObjectsSize;
if (i > 0) {
//LOGI("Closing file descriptors for %d objects...", mObjectsSize);
}
while (i > 0) {
i--;
const flat_binder_object* flat
= reinterpret_cast<flat_binder_object*>(mData+mObjects[i]);
if (flat->type == BINDER_TYPE_FD) {
//LOGI("Closing fd: %ld/n", flat->handle);
close(flat->handle);
}
}
}

const uint8_t* Parcel::ipcData() const
{
return mData;
}

size_t Parcel::ipcDataSize() const
{
return (mDataSize > mDataPos ? mDataSize : mDataPos);
}

const size_t* Parcel::ipcObjects() const
{
return mObjects;
}

size_t Parcel::ipcObjectsCount() const
{
return mObjectsSize;
}

void Parcel::ipcSetDataReference(const uint8_t* data, size_t dataSize,
const size_t* objects, size_t objectsCount, release_func relFunc, void* relCookie)
{
freeDataNoInit();
mError = NO_ERROR;
mData = const_cast<uint8_t*>(data);
mDataSize = mDataCapacity = dataSize;
//LOGI("setDataReference Setting data size of %p to %lu (pid=%d)/n", this, mDataSize, getpid());
mDataPos = 0;
LOGV("setDataReference Setting data pos of %p to %d/n", this, mDataPos);
mObjects = const_cast<size_t*>(objects);
mObjectsSize = mObjectsCapacity = objectsCount;
mNextObjectHint = 0;
mOwner = relFunc;
mOwnerCookie = relCookie;
scanForFds();
}

void Parcel::print(TextOutput& to, uint32_t flags) const
{
to << "Parcel(";

if (errorCheck() != NO_ERROR) {
const status_t err = errorCheck();
to << "Error: " << (void*)err << " /"" << strerror(-err) << "/"";
} else if (dataSize() > 0) {
const uint8_t* DATA = data();
to << indent << HexDump(DATA, dataSize()) << dedent;
const size_t* OBJS = objects();
const size_t N = objectsCount();
for (size_t i=0; i<N; i++) {
const flat_binder_object* flat
= reinterpret_cast<const flat_binder_object*>(DATA+OBJS[i]);
to << endl << "Object #" << i << " @ " << (void*)OBJS[i] << ": "
<< TypeCode(flat->type & 0x7f7f7f00)
<< " = " << flat->binder;
}
} else {
to << "NULL";
}

to << ")";
}

void Parcel::releaseObjects()
{
const sp<ProcessState> proc(ProcessState::self());
size_t i = mObjectsSize;
uint8_t* const data = mData;
size_t* const objects = mObjects;
while (i > 0) {
i--;
const flat_binder_object* flat
= reinterpret_cast<flat_binder_object*>(data+objects[i]);
release_object(proc, *flat, this);
}
}

void Parcel::acquireObjects()
{
const sp<ProcessState> proc(ProcessState::self());
size_t i = mObjectsSize;
uint8_t* const data = mData;
size_t* const objects = mObjects;
while (i > 0) {
i--;
const flat_binder_object* flat
= reinterpret_cast<flat_binder_object*>(data+objects[i]);
acquire_object(proc, *flat, this);
}
}

void Parcel::freeData()
{
freeDataNoInit();
initState();
}

void Parcel::freeDataNoInit()
{
if (mOwner) {
//LOGI("Freeing data ref of %p (pid=%d)/n", this, getpid());
mOwner(this, mData, mDataSize, mObjects, mObjectsSize, mOwnerCookie);
} else {
releaseObjects();
if (mData) free(mData);
if (mObjects) free(mObjects);
}
}

status_t Parcel::growData(size_t len)
{
size_t newSize = ((mDataSize+len)*3)/2;
return (newSize <= mDataSize)
? (status_t) NO_MEMORY
: continueWrite(newSize);
}

status_t Parcel::restartWrite(size_t desired)
{
if (mOwner) {
freeData();
return continueWrite(desired);
}

uint8_t* data = (uint8_t*)realloc(mData, desired);
if (!data && desired > mDataCapacity) {
mError = NO_MEMORY;
return NO_MEMORY;
}

releaseObjects();

if (data) {
mData = data;
mDataCapacity = desired;
}

mDataSize = mDataPos = 0;
LOGV("restartWrite Setting data size of %p to %d/n", this, mDataSize);
LOGV("restartWrite Setting data pos of %p to %d/n", this, mDataPos);

free(mObjects);
mObjects = NULL;
mObjectsSize = mObjectsCapacity = 0;
mNextObjectHint = 0;
mHasFds = false;
mFdsKnown = true;

return NO_ERROR;
}

status_t Parcel::continueWrite(size_t desired)
{
// If shrinking, first adjust for any objects that appear
// after the new data size.
size_t objectsSize = mObjectsSize;
if (desired < mDataSize) {
if (desired == 0) {
objectsSize = 0;
} else {
while (objectsSize > 0) {
if (mObjects[objectsSize-1] < desired)
break;
objectsSize--;
}
}
}

if (mOwner) {
// If the size is going to zero, just release the owner's data.
if (desired == 0) {
freeData();
return NO_ERROR;
}

// If there is a different owner, we need to take
// posession.
uint8_t* data = (uint8_t*)malloc(desired);
if (!data) {
mError = NO_MEMORY;
return NO_MEMORY;
}
size_t* objects = NULL;

if (objectsSize) {
objects = (size_t*)malloc(objectsSize*sizeof(size_t));
if (!objects) {
mError = NO_MEMORY;
return NO_MEMORY;
}

// Little hack to only acquire references on objects
// we will be keeping.
size_t oldObjectsSize = mObjectsSize;
mObjectsSize = objectsSize;
acquireObjects();
mObjectsSize = oldObjectsSize;
}

if (mData) {
memcpy(data, mData, mDataSize < desired ? mDataSize : desired);
}
if (objects && mObjects) {
memcpy(objects, mObjects, objectsSize*sizeof(size_t));
}
//LOGI("Freeing data ref of %p (pid=%d)/n", this, getpid());
mOwner(this, mData, mDataSize, mObjects, mObjectsSize, mOwnerCookie);
mOwner = NULL;

mData = data;
mObjects = objects;
mDataSize = (mDataSize < desired) ? mDataSize : desired;
LOGV("continueWrite Setting data size of %p to %d/n", this, mDataSize);
mDataCapacity = desired;
mObjectsSize = mObjectsCapacity = objectsSize;
mNextObjectHint = 0;

} else if (mData) {
if (objectsSize < mObjectsSize) {
// Need to release refs on any objects we are dropping.
const sp<ProcessState> proc(ProcessState::self());
for (size_t i=objectsSize; i<mObjectsSize; i++) {
const flat_binder_object* flat
= reinterpret_cast<flat_binder_object*>(mData+mObjects[i]);
if (flat->type == BINDER_TYPE_FD) {
// will need to rescan because we may have lopped off the only FDs
mFdsKnown = false;
}
release_object(proc, *flat, this);
}
size_t* objects =
(size_t*)realloc(mObjects, objectsSize*sizeof(size_t));
if (objects) {
mObjects = objects;
}
mObjectsSize = objectsSize;
mNextObjectHint = 0;
}

// We own the data, so we can just do a realloc().
if (desired > mDataCapacity) {
uint8_t* data = (uint8_t*)realloc(mData, desired);
if (data) {
mData = data;
mDataCapacity = desired;
} else if (desired > mDataCapacity) {
mError = NO_MEMORY;
return NO_MEMORY;
}
} else {
mDataSize = desired;
LOGV("continueWrite Setting data size of %p to %d/n", this, mDataSize);
if (mDataPos > desired) {
mDataPos = desired;
LOGV("continueWrite Setting data pos of %p to %d/n", this, mDataPos);
}
}

} else {
// This is the first data. Easy!
uint8_t* data = (uint8_t*)malloc(desired);
if (!data) {
mError = NO_MEMORY;
return NO_MEMORY;
}

if(!(mDataCapacity == 0 && mObjects == NULL
&& mObjectsCapacity == 0)) {
LOGE("continueWrite: %d/%p/%d/%d", mDataCapacity, mObjects, mObjectsCapacity, desired);
}

mData = data;
mDataSize = mDataPos = 0;
LOGV("continueWrite Setting data size of %p to %d/n", this, mDataSize);
LOGV("continueWrite Setting data pos of %p to %d/n", this, mDataPos);
mDataCapacity = desired;
}

return NO_ERROR;
}

void Parcel::initState()
{
mError = NO_ERROR;
mData = 0;
mDataSize = 0;
mDataCapacity = 0;
mDataPos = 0;
LOGV("initState Setting data size of %p to %d/n", this, mDataSize);
LOGV("initState Setting data pos of %p to %d/n", this, mDataPos);
mObjects = NULL;
mObjectsSize = 0;
mObjectsCapacity = 0;
mNextObjectHint = 0;
mHasFds = false;
mFdsKnown = true;
mOwner = NULL;
}

void Parcel::scanForFds() const
{
bool hasFds = false;
for (size_t i=0; i<mObjectsSize; i++) {
const flat_binder_object* flat
= reinterpret_cast<const flat_binder_object*>(mData + mObjects[i]);
if (flat->type == BINDER_TYPE_FD) {
hasFds = true;
break;
}
}
mHasFds = hasFds;
mFdsKnown = true;
}

}; // namespace android

本文的源代码使用的是Android 2.1版本号。

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