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Android的IPC机制Binder
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第一部分 Binder的組成?
1.1 驅(qū)動(dòng)程序部分驅(qū)動(dòng)程序的部分在以下的文件夾中：
Java代碼?
kernel/include/linux/binder.h ?? kernel/drivers/android/binder.c??
Java代碼??
kernel/include/linux/binder.h?? kernel/drivers/android/binder.c??
??? binder驅(qū)動(dòng)程序是一個(gè)miscdevice，主設(shè)備號(hào)為10，此設(shè)備號(hào)使用動(dòng)態(tài)獲得（MISC_DYNAMIC_MINOR），其設(shè)備的節(jié)點(diǎn)為：?
/dev/binder?
??? binder驅(qū)動(dòng)程序會(huì)在proc文件系統(tǒng)中建立自己的信息，其文件夾為/proc/binder，其中包含如下內(nèi)容：?
proc目錄：調(diào)用Binder各個(gè)進(jìn)程的內(nèi)容?
state文件：使用函數(shù)binder_read_proc_state?
stats文件：使用函數(shù)binder_read_proc_stats?
transactions文件：使用函數(shù)binder_read_proc_transactions?
transaction_log文件：使用函數(shù)binder_read_proc_transaction_log，其參數(shù)為binder_transaction_log (類型為struct binder_transaction_log)?
failed_transaction_log文件：使用函數(shù)binder_read_proc_transaction_log 其參數(shù)為?
binder_transaction_log_failed (類型為struct binder_transaction_log)?
??? 在binder文件被打開后，其私有數(shù)據(jù)（private_data）的類型：?
struct binder_proc?
??? 在這個(gè)數(shù)據(jù)結(jié)構(gòu)中，主要包含了當(dāng)前進(jìn)程、進(jìn)程ID、內(nèi)存映射信息、Binder的統(tǒng)計(jì)信息和線程信息等。?
??? 在用戶空間對(duì)Binder驅(qū)動(dòng)程序進(jìn)行控制主要使用的接口是mmap、poll和ioctl，ioctl主要使用的ID為：
Java代碼?
#define?BINDER_WRITE_READ????????_IOWR('b',?1,?struct?binder_write_read) ?? #define?BINDER_SET_IDLE_TIMEOUT??_IOW('b',?3,?int64_t) ?? #define?BINDER_SET_MAX_THREADS???_IOW('b',?5,?size_t) ?? #define?BINDER_SET_IDLE_PRIORITY?_IOW('b',?6,?int) ?? #define?BINDER_SET_CONTEXT_MGR???_IOW('b',?7,?int) ?? #define?BINDER_THREAD_EXIT???????_IOW('b',?8,?int) ?? #define?BINDER_VERSION???????????_IOWR('b',?9,?struct?binder_version)??
Java代碼??
#define?BINDER_WRITE_READ????????_IOWR('b',?1,?struct?binder_write_read)?? #define?BINDER_SET_IDLE_TIMEOUT??_IOW('b',?3,?int64_t)?? #define?BINDER_SET_MAX_THREADS???_IOW('b',?5,?size_t)?? #define?BINDER_SET_IDLE_PRIORITY?_IOW('b',?6,?int)?? #define?BINDER_SET_CONTEXT_MGR???_IOW('b',?7,?int)?? #define?BINDER_THREAD_EXIT???????_IOW('b',?8,?int)?? #define?BINDER_VERSION???????????_IOWR('b',?9,?struct?binder_version)??
??? BR_XXX等宏為BinderDriverReturnProtocol，表示Binder驅(qū)動(dòng)返回協(xié)議。?
??? BC_XXX等宏為BinderDriverCommandProtocol，表示Binder驅(qū)動(dòng)命令協(xié)議。?
??? binder_thread是Binder驅(qū)動(dòng)程序中使用的另外一個(gè)重要的數(shù)據(jù)結(jié)構(gòu)，數(shù)據(jù)結(jié)構(gòu)的定義如下所示：
Java代碼?
struct?binder_thread?{ ?? ??????struct?binder_proc?*proc; ?? ?????struct?rb_node?rb_node; ?? ?????int?pid; ?? ?????int?looper; ?? ?????struct?binder_transaction?*transaction_stack; ?? ?????struct?list_head?todo; ?? ?????uint32_t?return_error; ?? ?????uint32_t?return_error2; ?? ?????wait_queue_head_t?wait; ?? ?????struct?binder_stats?stats; ?? };??
Java代碼??
struct?binder_thread?{?? ??????struct?binder_proc?*proc;?? ?????struct?rb_node?rb_node;?? ?????int?pid;?? ?????int?looper;?? ?????struct?binder_transaction?*transaction_stack;?? ?????struct?list_head?todo;?? ?????uint32_t?return_error;?? ?????uint32_t?return_error2;?? ?????wait_queue_head_t?wait;?? ?????struct?binder_stats?stats;?? };??
??? binder_thread 的各個(gè)成員信息是從rb_node中得出。?
??? BINDER_WRITE_READ是最重要的ioctl，它使用一個(gè)數(shù)據(jù)結(jié)構(gòu)binder_write_read定義讀寫的數(shù)據(jù)。
Java代碼?
struct?binder_write_read?{ ?? ?????signed?long?write_size; ?? ?????signed?long?write_consumed; ?? ?????unsigned?long?write_buffer; ?? ?????signed?long?read_size; ?? ?????signed?long?read_consumed; ?? ?????unsigned?long?read_buffer; ?? };??
Java代碼??
struct?binder_write_read?{?? ?????signed?long?write_size;?? ?????signed?long?write_consumed;?? ?????unsigned?long?write_buffer;?? ?????signed?long?read_size;?? ?????signed?long?read_consumed;?? ?????unsigned?long?read_buffer;?? };??
1.2 servicemanager部分??????? servicemanager是一個(gè)守護(hù)進(jìn)程，用于這個(gè)進(jìn)程的和/dev/binder通訊，從而達(dá)到管理系統(tǒng)中各個(gè)服務(wù)的作用。?
??????? 可執(zhí)行程序的路徑：?
??????? /system/bin/servicemanager????????
開源版本文件的路徑：
Java代碼?
frameworks/base/cmds/servicemanager/binder.h ?? frameworks/base/cmds/servicemanager/binder.c ?? frameworks/base/cmds/servicemanager/service_manager.c??
Java代碼??
frameworks/base/cmds/servicemanager/binder.h?? frameworks/base/cmds/servicemanager/binder.c?? frameworks/base/cmds/servicemanager/service_manager.c??
?????? 程序執(zhí)行的流程：?
open()：打開binder驅(qū)動(dòng)?
mmap()：映射一個(gè)128*1024字節(jié)的內(nèi)存?
ioctl(BINDER_SET_CONTEXT_MGR)：設(shè)置上下文為mgr?
?????? 進(jìn)入主循環(huán)binder_loop()?
???????????? ioctl(BINDER_WRITE_READ)，讀取?
?????????????????????? binder_parse()進(jìn)入binder處理過程循環(huán)處理?
???????? binder_parse()的處理，調(diào)用返回值：?
??????? 當(dāng)處理BR_TRANSACTION的時(shí)候，調(diào)用svcmgr_handler()處理增加服務(wù)、檢查服務(wù)等工作。各種服務(wù)存放在一個(gè)鏈表（svclist）中。其中調(diào)用binder_等開頭的函數(shù)，又會(huì)調(diào)用ioctl的各種命令。?
??????? 處理BR_REPLY的時(shí)候，填充binder_io類型的數(shù)據(jù)結(jié)?
1.3 binder的庫(kù)的部分?
??? binder相關(guān)的文件作為Android的uitls庫(kù)的一部分，這個(gè)庫(kù)編譯后的名稱為libutils.so，是Android系統(tǒng)中的一個(gè)公共庫(kù)。?
??? 主要文件的路徑如下所示：
Java代碼?
frameworks/base/include/utils/* ?? frameworks/base/libs/utils/*??
Java代碼??
frameworks/base/include/utils/*?? frameworks/base/libs/utils/*??
???
??? 主要的類為：?
RefBase.h :?
??? 引用計(jì)數(shù)，定義類RefBase。?
Parcel.h :?
??? 為在IPC中傳輸?shù)臄?shù)據(jù)定義容器，定義類Parcel?
IBinder.h：?
??? Binder對(duì)象的抽象接口， 定義類IBinder?
Binder.h：?
??? Binder對(duì)象的基本功能， 定義類Binder和BpRefBase?
BpBinder.h：?
BpBinder的功能，定義類BpBinder?
IInterface.h：?
為抽象經(jīng)過Binder的接口定義通用類，?
??? 定義類IInterface，類模板BnInterface，類模板BpInterface?
ProcessState.h?
??? 表示進(jìn)程狀態(tài)的類，定義類ProcessState?
IPCThreadState.h?
??? 表示IPC線程的狀態(tài)，定義類IPCThreadState?
各個(gè)類之間的關(guān)系如下所示：?
??? 在IInterface.h中定義的BnInterface和BpInterface是兩個(gè)重要的模版，這是為各種程序中使用的。?
BnInterface模版的定義如下所示：
Java代碼?
template ?? class?BnInterface?:?public?INTERFACE,?public?BBinder ?? { ?? public: ?? ????virtual?sp??queryLocalInterface(const?String16&?_descriptor); ?? ????virtual?String16????????getInterfaceDescriptor()?const; ?? protected: ?? ????virtual?IBinder*????????onAsBinder(); ?? }; ?? ?????BnInterface模版的定義如下所示： ?? template ?? class?BpInterface?:?public?INTERFACE,?public?BpRefBase ?? { ?? public: ?? ????????????????????????????BpInterface(const?sp&?remote); ?? protected: ?? ????virtual?IBinder*????onAsBinder(); ?? };??
Java代碼??
template?? class?BnInterface?:?public?INTERFACE,?public?BBinder?? {?? public:?? ????virtual?sp??queryLocalInterface(const?String16&?_descriptor);?? ????virtual?String16????????getInterfaceDescriptor()?const;?? protected:?? ????virtual?IBinder*????????onAsBinder();?? };?? ?????BnInterface模版的定義如下所示：?? template?? class?BpInterface?:?public?INTERFACE,?public?BpRefBase?? {?? public:?? ????????????????????????????BpInterface(const?sp&?remote);?? protected:?? ????virtual?IBinder*????onAsBinder();?? };??
???????? 這兩個(gè)模版在使用的時(shí)候，起到得作用實(shí)際上都是雙繼承：使用者定義一個(gè)接口INTERFACE，然后使用BnInterface和BpInterface兩個(gè)模版結(jié)合自己的接口，構(gòu)建自己的BnXXX和BpXXX兩個(gè)類。?
???????? DECLARE_META_INTERFACE和IMPLEMENT_META_INTERFACE兩個(gè)宏用于幫助BpXXX類的實(shí)現(xiàn)：
Java代碼?
#define?DECLARE_META_INTERFACE(INTERFACE)???????????????????????????????\ ?? ????static?const?String16?descriptor;???????????????????????????????????\ ?? ????static?sp?asInterface(const?sp&?obj);????????\ ?? ????virtual?String16?getInterfaceDescriptor()?const;????????????????????\ ?? #define?IMPLEMENT_META_INTERFACE(INTERFACE,?NAME)???????????????????????\ ?? ????const?String16?I##INTERFACE::descriptor(NAME);??????????????????????\ ?? ????String16?I##INTERFACE::getInterfaceDescriptor()?const?{?????????????\ ?? ????????return?I##INTERFACE::descriptor;????????????????????????????????\ ?? ????}???????????????????????????????????????????????????????????????????\ ?? ????sp?I##INTERFACE::asInterface(const?sp&?obj)??\ ?? ????{???????????????????????????????????????????????????????????????????\ ?? ????????sp?intr;??????????????????????????????????????????\ ?? ????????if?(obj?!=?NULL)?{??????????????????????????????????????????????\ ?? ????????????intr?=?static_cast(??????????????????????????\ ?? ????????????????obj->queryLocalInterface(???????????????????????????????\ ?? ????????????????????????I##INTERFACE::descriptor).get());???????????????\ ?? ????????????if?(intr?==?NULL)?{?????????????????????????????????????????\ ?? ????????????????intr?=?new?Bp##INTERFACE(obj);??????????????????????????\ ?? ????????????}???????????????????????????????????????????????????????????\ ?? ????????}???????????????????????????????????????????????????????????????\ ?? ????????return?intr;????????????????????????????????????????????????????\ ?? ????}??
Java代碼??
#define?DECLARE_META_INTERFACE(INTERFACE)???????????????????????????????\?? ????static?const?String16?descriptor;???????????????????????????????????\?? ????static?sp?asInterface(const?sp&?obj);????????\?? ????virtual?String16?getInterfaceDescriptor()?const;????????????????????\?? #define?IMPLEMENT_META_INTERFACE(INTERFACE,?NAME)???????????????????????\?? ????const?String16?I##INTERFACE::descriptor(NAME);??????????????????????\?? ????String16?I##INTERFACE::getInterfaceDescriptor()?const?{?????????????\?? ????????return?I##INTERFACE::descriptor;????????????????????????????????\?? ????}???????????????????????????????????????????????????????????????????\?? ????sp?I##INTERFACE::asInterface(const?sp&?obj)??\?? ????{???????????????????????????????????????????????????????????????????\?? ????????sp?intr;??????????????????????????????????????????\?? ????????if?(obj?!=?NULL)?{??????????????????????????????????????????????\?? ????????????intr?=?static_cast(??????????????????????????\?? ????????????????obj->queryLocalInterface(???????????????????????????????\?? ????????????????????????I##INTERFACE::descriptor).get());???????????????\?? ????????????if?(intr?==?NULL)?{?????????????????????????????????????????\?? ????????????????intr?=?new?Bp##INTERFACE(obj);??????????????????????????\?? ????????????}???????????????????????????????????????????????????????????\?? ????????}???????????????????????????????????????????????????????????????\?? ????????return?intr;????????????????????????????????????????????????????\?? ????}??
??
?? 在定義自己的類的時(shí)候，只需要使用DECLARE_META_INTERFACE和IMPLEMENT_META_INTERFACE兩個(gè)接口，并?
結(jié)合類的名稱，就可以實(shí)現(xiàn)BpInterface中的asInterface()和getInterfaceDescriptor()兩個(gè)函數(shù)。?
第二部分 Binder的運(yùn)作?
2.1 Binder的工作機(jī)制?
????? Service Manager是一個(gè)守護(hù)進(jìn)程，它負(fù)責(zé)啟動(dòng)各個(gè)進(jìn)程之間的服務(wù)，對(duì)于相關(guān)的兩個(gè)需要通訊的進(jìn)程，它們通過調(diào)用libutil.so庫(kù)實(shí)現(xiàn)通訊，而真正通訊的機(jī)制，是內(nèi)核空間中的一塊共享內(nèi)存。?
??????
2.2 從應(yīng) 用程序的角度看Binder?
從應(yīng)用程序的角度看Binder一共有三個(gè)方面：?
Native 本地：例如BnABC，這是一個(gè)需要被繼承和實(shí)現(xiàn)的類。?
Proxy 代理：例如BpABC，這是一個(gè)在接口框架中被實(shí)現(xiàn)，但是在接口中沒有體現(xiàn)的類。?
客戶端：例如客戶端得到一個(gè)接口ABC，在調(diào)用的時(shí)候?qū)嶋H上被調(diào)用的是BpABC?
本地功能（Bn）部分做的：?
??? 實(shí)現(xiàn)BnABC:: BnTransact()?
??? 注冊(cè)服務(wù)：IServiceManager：：AddService?
代理部分（Bp）做的：?
??? 實(shí)現(xiàn)幾個(gè)功能函數(shù)，調(diào)用BpABC::remote()->transact()?
客戶端做的：?
??? 獲得ABC接口，然后調(diào)用接口（實(shí)際上調(diào)用了BpABC，繼而通過IPC調(diào)用了BnABC，然后調(diào)用了具體的功能）?
?????? 在程序的實(shí)現(xiàn)過程中BnABC和BpABC是雙繼承了接口ABC。一般來說BpABC是一個(gè)實(shí)現(xiàn)類，這個(gè)實(shí)現(xiàn)類不需要在接口中體現(xiàn)，它實(shí)際上負(fù)責(zé)的只是通訊功能，不執(zhí)行具體的功能；BnABC則是一個(gè)接口類，需要一個(gè)真正工作的類來繼承、實(shí)現(xiàn)它，這個(gè)類才是真正執(zhí)行具體功能的類。?
?????? 在客戶端中，從ISeriviceManager中獲得一個(gè)ABC的接口，客戶端調(diào)用這個(gè)接口，實(shí)際上是在調(diào)用BpABC，而BpABC又通過Binder的IPC機(jī)制和BnABC通訊，BnABC的實(shí)現(xiàn)類在后面執(zhí)行。?
事實(shí)上，?
服務(wù)器?
的具體實(shí)現(xiàn)和客戶端是兩個(gè)不同的進(jìn)程，如果不考慮進(jìn)程間通訊的過程，從調(diào)用者的角度，似乎客戶端在直接調(diào)用另外一個(gè)進(jìn)程間的函數(shù)——當(dāng)然這個(gè)函數(shù)必須是接口ABC中定義的。?
2.3 ISericeManager的作用?
??? ISericeManager涉及的兩個(gè)文件是ISericeManager.h和ISericeManager.cpp。這兩個(gè)文件基本上是?
ISericeManager。ISericeManager是系統(tǒng)最先被啟動(dòng)的服務(wù)。非常值得注意的是：ISericeManager本地功能并沒有使?
現(xiàn)，它實(shí)際上由ServiceManager守護(hù)進(jìn)程執(zhí)行，而用戶程序通過調(diào)用BpServiceManager來獲得其他的服務(wù)。?
????? 在ISericeManager.h中定義了一個(gè)接口，用于得到默認(rèn)的ISericeManager：?
??????? sp defaultServiceManager();?
???? 這時(shí)得到的ISericeManager實(shí)際上是一個(gè)全局的ISericeManager。?
第三部分 程序中Binder的具體實(shí)現(xiàn)?
3.1 一個(gè)利用接口的具體實(shí)現(xiàn)?
??? PermissionController也是libutils中定義的一個(gè)有關(guān)權(quán)限控制的接口，它一共包含兩個(gè)文件：IPermissionController.h和IPermissionController.cpp這個(gè)結(jié)構(gòu)在所有類的實(shí)現(xiàn)中都是類似的。?
???? 頭文件IPermissionController.h的主要內(nèi)容是定義IPermissionController接口和類BnPermissionController：
Java代碼?
class?IPermissionController?:?public?IInterface ?? { ?? public: ?? ????DECLARE_META_INTERFACE(PermissionController); ?? ????virtual?bool???checkPermission(const?String16&?permission,int32_t?pid,?int32_t?uid)?=?0; ?? ????enum?{ ?? ????????CHECK_PERMISSION_TRANSACTION?=?IBinder::FIRST_CALL_TRANSACTION ?? ????}; ?? }; ?? class?BnPermissionController?:?public?BnInterface ?? { ?? public: ?? ????virtual?status_t????onTransact(?uint32_t?code, ?? ????????????????????????????????????const?Parcel&?data, ?? ????????????????????????????????????Parcel*?reply, ?? ????????????????????????????????????uint32_t?flags?=?0); ?? };??
Java代碼??
class?IPermissionController?:?public?IInterface?? {?? public:?? ????DECLARE_META_INTERFACE(PermissionController);?? ????virtual?bool???checkPermission(const?String16&?permission,int32_t?pid,?int32_t?uid)?=?0;?? ????enum?{?? ????????CHECK_PERMISSION_TRANSACTION?=?IBinder::FIRST_CALL_TRANSACTION?? ????};?? };?? class?BnPermissionController?:?public?BnInterface?? {?? public:?? ????virtual?status_t????onTransact(?uint32_t?code,?? ????????????????????????????????????const?Parcel&?data,?? ????????????????????????????????????Parcel*?reply,?? ????????????????????????????????????uint32_t?flags?=?0);?? };??
??? IPermissionController是一個(gè)接口類，只有checkPermission()一個(gè)純虛函數(shù)。?
BnPermissionController繼承了以BnPermissionController實(shí)例化模版類BnInterface。因?
此，BnPermissionController，事實(shí)上BnPermissionController雙繼承了BBinder和?
IPermissionController。?
??? 實(shí)現(xiàn)文件IPermissionController.cpp中，首先實(shí)現(xiàn)了一個(gè)BpPermissionController。
Java代碼?
class?BpPermissionController?:?public?BpInterface ?? { ?? public: ?? ????BpPermissionController(const?sp&?impl) ?? ????????:?BpInterface(impl) ?? ????{ ?? ????} ?? ????virtual?bool?checkPermission(const?String16&?permission,?int32_t?pid,?int32_t?uid) ?? ????{ ?? ????????Parcel?data,?reply; ?? ????????data.writeInterfaceToken(IPermissionController:: ?? ???????????????????????????????????????getInterfaceDescriptor()); ?? ????????data.writeString16(permission); ?? ????????data.writeInt32(pid); ?? ????????data.writeInt32(uid); ?? ????????remote()->transact(CHECK_PERMISSION_TRANSACTION,?data,?&reply); ?? ????????if?(reply.readInt32()?!=?0)?return?0; ?? ????????return?reply.readInt32()?!=?0; ?? ????} ?? };??
Java代碼??
class?BpPermissionController?:?public?BpInterface?? {?? public:?? ????BpPermissionController(const?sp&?impl)?? ????????:?BpInterface(impl)?? ????{?? ????}?? ????virtual?bool?checkPermission(const?String16&?permission,?int32_t?pid,?int32_t?uid)?? ????{?? ????????Parcel?data,?reply;?? ????????data.writeInterfaceToken(IPermissionController::?? ???????????????????????????????????????getInterfaceDescriptor());?? ????????data.writeString16(permission);?? ????????data.writeInt32(pid);?? ????????data.writeInt32(uid);?? ????????remote()->transact(CHECK_PERMISSION_TRANSACTION,?data,?&reply);?? ????????if?(reply.readInt32()?!=?0)?return?0;?? ????????return?reply.readInt32()?!=?0;?? ????}?? };??
IMPLEMENT_META_INTERFACE(PermissionController, "android.os.IPermissionController");?
BpPermissionController繼承了BpInterface，它本身是一個(gè)?
已經(jīng)實(shí)現(xiàn)的類，而且并沒有在接口中體現(xiàn)。這個(gè)類按照格式寫就可以，在實(shí)現(xiàn)checkPermission()函數(shù)的過程中，使用Parcel作為傳輸數(shù)據(jù)?
的容器，傳輸中時(shí)候transact()函數(shù)，其參數(shù)需要包含枚舉值CHECK_PERMISSION_TRANSACTION。?
IMPLEMENT_META_INTERFACE用于扶助生成。?
??? BnPermissionController中實(shí)現(xiàn)的onTransact()函數(shù)如下所示：
Java代碼?
status_t?BnPermissionController::?BnTransact( ?? ????uint32_t?code,?const?Parcel&?data,?Parcel*?reply,?uint32_t?flags) ?? { ?? ????switch(code)?{ ?? ????????case?CHECK_PERMISSION_TRANSACTION:?{ ?? ????????????CHECK_INTERFACE(IPermissionController,?data,?reply); ?? ????????????String16?permission?=?data.readString16(); ?? ????????????int32_t?pid?=?data.readInt32(); ?? ????????????int32_t?uid?=?data.readInt32(); ?? ????????????bool?res?=?checkPermission(permission,?pid,?uid); ?? ????????????reply->writeInt32(0); ?? ????????????reply->writeInt32(res???1?:?0); ?? ????????????return?NO_ERROR; ?? ????????}?break; ?? ????????default: ?? ????????????return?BBinder::?BnTransact(code,?data,?reply,?flags); ?? ????} ?? }??
Java代碼??
status_t?BnPermissionController::?BnTransact(?? ????uint32_t?code,?const?Parcel&?data,?Parcel*?reply,?uint32_t?flags)?? {?? ????switch(code)?{?? ????????case?CHECK_PERMISSION_TRANSACTION:?{?? ????????????CHECK_INTERFACE(IPermissionController,?data,?reply);?? ????????????String16?permission?=?data.readString16();?? ????????????int32_t?pid?=?data.readInt32();?? ????????????int32_t?uid?=?data.readInt32();?? ????????????bool?res?=?checkPermission(permission,?pid,?uid);?? ????????????reply->writeInt32(0);?? ????????????reply->writeInt32(res???1?:?0);?? ????????????return?NO_ERROR;?? ????????}?break;?? ????????default:?? ????????????return?BBinder::?BnTransact(code,?data,?reply,?flags);?? ????}?? }??
???? 在onTransact()函數(shù)中根據(jù)枚舉值判斷數(shù)據(jù)使用的方式。注意，由于BnPermissionController也是繼承了類?
IPermissionController，但是純虛函數(shù)checkPermission()依然沒有實(shí)現(xiàn)。因此這個(gè)?
BnPermissionController類并不能實(shí)例化，它其實(shí)也還是一個(gè)接口，需要一個(gè)實(shí)現(xiàn)類來繼承它，那才是實(shí)現(xiàn)具體功能的類。?
3.2 BnABC的實(shí)現(xiàn)?
??? 本地服務(wù)啟動(dòng)后將形成一個(gè)守護(hù)進(jìn)程，具體的本地服務(wù)是由一個(gè)實(shí)現(xiàn)類繼承BnABC來實(shí)現(xiàn)的，這個(gè)服務(wù)的名稱通常叫做ABC。?
??? 在其中，通常包含了一個(gè)instantiate()函數(shù)，這個(gè)函數(shù)一般按照如下的方式實(shí)現(xiàn)：?
void ABC::instantiate() {?
??? defaultServiceManager()->addService(?
??????????? String16("XXX.ABC"), new ABC ());?
}?
??? 按照這種方式，通過調(diào)用defaultServiceManager()函數(shù)，將增加一個(gè)名為"XXX.ABC"的服務(wù)。?
??? 在這個(gè)defaultServiceManager()函數(shù)中調(diào)用了：?
ProcessState::self()->getContextObject(NULL));?
??? IPCThreadState* ipc = IPCThreadState::self();?
?? IPCThreadState::talkWithDriver()?
在ProcessState 類建立的過程中調(diào)用open_driver()打開?
驅(qū)動(dòng)?
程序，在talkWithDriver()的執(zhí)行過程中。?
3.3 BpABC調(diào)用的實(shí)現(xiàn)?
??? BpABC調(diào)用的過程主要通過mRemote()->transact() 來傳輸數(shù)據(jù)，mRemote()是BpRefBase的成員，它是一個(gè)IBinder。這個(gè)調(diào)用過程如下所示：?
???
Java代碼?
mRemote()->transact() ?? ????Process::self() ?? ????IPCThreadState::self()->transact() ?? ????writeTransactionData() ?? ????waitForResponse() ?? ????talkWithDriver() ?? ????ioctl(fd,?BINDER_WRITE_READ,?&bwr)??
Java代碼??
mRemote()->transact()?? ????Process::self()?? ????IPCThreadState::self()->transact()?? ????writeTransactionData()?? ????waitForResponse()?? ????talkWithDriver()?? ????ioctl(fd,?BINDER_WRITE_READ,?&bwr)??
??? 在IPCThreadState::executeCommand()函數(shù)中，實(shí)現(xiàn)傳輸操作。
(hanchao3c?Android開發(fā)者論壇原創(chuàng)）
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