转载：http://blog.csdn.net/innost/article/details/6041412

ANDROID搞了大概5个月了，总感觉到它的这个java封装非常的不爽。这次下载了Froyo的源码，准备好好分析下Android的运行流程。一直有个暗想--能否替换掉JAVA层？搞android最麻烦的就是老记不住它那几个文件的位置，这里将给出详细的路径，方便其他看客了解。

没有固定的顺序，不过大概就是从启动开始的一些东西吧。我的想法是对android了解越多，才越可能在此基础上做最好最完善的改动。真的很不喜欢它的java层。

一 用户空间init

我这里不分析linux启动的那第一个程序init。

init代码在/system/core/init/init.c。感兴趣的可从main函数开始分析

android的其他重要进程都是init加载init.rc配置文件来fork的。其中，最重要的init.rc位于source/system/core/rootdir下。

init.rc有它特有的语法，可google一下就知道了。

二 zygote的诞生

zygote程序是有app_process弄出来的，app_process的启动在init.rc中有对应行。

service zygote /system/bin/app_process -Xzygote /system/bin --zygote --start-system-server

//第一个zygote是这个服务的名字，实际启动的程序位于system/bin下的app_process,后面是这个程序的启动参数
socket zygote stream 666

//这个表示init将创建一个unix域的socket，666是rwx的读写执行权限。
onrestart write /sys/android_power/request_state wake
onrestart write /sys/power/state on
onrestart restart media

其中，app_process位于/frameworks/base/cmds/app_process/app_main.cpp中。

下面分析它的mian函数。

[cpp] view plain copy print ?

1. intmain(intargc,constchar*constargv[])
2. {
3. //argc=5
4. //argv=["/system/bin/app_process""-Xzygote""/system/bin""--zygote""--start-system-server"]
5. //TheseareglobalvariablesinProcessState.cpp
6. mArgC=argc;//全局变量
7. mArgV=argv;//全局变量
9. mArgLen=0;
10. for(inti=0;i<argc;i++){
11. mArgLen+=strlen(argv[i])+1;
12. }
13. mArgLen--;
15. AppRuntimeruntime;//定义AppRuntime
16. constchar*arg;
17. constchar*argv0;
19. argv0=argv[0];//argv0="/system/bin/app_process"
21. //Processcommandlinearguments
22. //ignoreargv[0]
23. argc--;
24. argv++;
26. //Everythingupto'--'orfirstnon'-'arggoestothevm
28. inti=runtime.addVmArguments(argc,argv);//将参数加到虚拟机，待会分析,应该是把-Xzygote加入虚拟机了
30. //Nextargisparentdirectory
31. if(i<argc){
32. runtime.mParentDir=argv[i++];//设置父目录为/system/bin
33. }
34. //
35. //Nextargisstartupclassnameor"--zygote"
36. if(i<argc){
37. arg=argv[i++];
38. if(0==strcmp("--zygote",arg)){
39. boolstartSystemServer=(i<argc)?
40. strcmp(argv[i],"--start-system-server")==0:false;//正常情况是true
41. setArgv0(argv0,"zygote");
42. set_process_name("zygote");
43. runtime.start("com.android.internal.os.ZygoteInit",
44. startSystemServer);//启动java的zygoteInit
45. }else{
46. set_process_name(argv0);
48. runtime.mClassName=arg;
50. //Remainderofargsgetpassedtostartupclassmain()
51. runtime.mArgC=argc-i;
52. runtime.mArgV=argv+i;
54. LOGV("Appprocessisstartingwithpid=%d,class=%s./n",
55. getpid(),runtime.getClassName());
56. runtime.start();
57. }
58. }else{
59. LOG_ALWAYS_FATAL("app_process:noclassnameor--zygotesupplied.");
60. fprintf(stderr,"Error:noclassnameor--zygotesupplied./n");
61. app_usage();
62. return10;
63. }
65. }

int main(int argc, const char* const argv[]) { //argc = 5 //argv=["/system/bin/app_process" "-Xzygote" "/system/bin" "--zygote" "--start-system-server"] // These are global variables in ProcessState.cpp mArgC = argc; //全局变量 mArgV = argv; //全局变量 mArgLen = 0; for (int i=0; i<argc; i++) { mArgLen += strlen(argv[i]) + 1; } mArgLen--; AppRuntime runtime;//定义AppRuntime const char *arg; const char *argv0; argv0 = argv[0]; //argv0="/system/bin/app_process" // Process command line arguments // ignore argv[0] argc--; argv++; // Everything up to '--' or first non '-' arg goes to the vm int i = runtime.addVmArguments(argc, argv);//将参数加到虚拟机，待会分析,应该是把-Xzygote加入虚拟机了 // Next arg is parent directory if (i < argc) { runtime.mParentDir = argv[i++]; //设置父目录为/system/bin } // // Next arg is startup classname or "--zygote" if (i < argc) { arg = argv[i++]; if (0 == strcmp("--zygote", arg)) { bool startSystemServer = (i < argc) ? strcmp(argv[i], "--start-system-server") == 0 : false;//正常情况是true setArgv0(argv0, "zygote"); set_process_name("zygote"); runtime.start("com.android.internal.os.ZygoteInit", startSystemServer);//启动java的zygoteInit } else { set_process_name(argv0); runtime.mClassName = arg; // Remainder of args get passed to startup class main() runtime.mArgC = argc-i; runtime.mArgV = argv+i; LOGV("App process is starting with pid=%d, class=%s./n", getpid(), runtime.getClassName()); runtime.start(); } } else { LOG_ALWAYS_FATAL("app_process: no class name or --zygote supplied."); fprintf(stderr, "Error: no class name or --zygote supplied./n"); app_usage(); return 10; } }

从上面代码注释可以看出，很多工作都交给了Runtime对象来处理，这个runtime对象也是在这个cpp文件中定义的。我们来看一下。

[cpp:collapse] + expand source view plain copy print ?

1. classAppRuntime:publicAndroidRuntime//基类是AndroidRuntime，待会分析下是干嘛的
2. {
3. public:
4. AppRuntime()
5. :mParentDir(NULL)
6. ,mClassName(NULL)
7. ,mArgC(0)
8. ,mArgV(NULL)
9. {
10. }
12. #if0
13. //thisappearstobeunused
14. constchar*getParentDir()const
15. {
16. returnmParentDir;
17. }
18. #endif
20. constchar*getClassName()const
21. {
22. returnmClassName;
23. }
25. virtualvoidonStarted()//下面几个onXXX应该是回调用的，可能是JNI回调
26. {
27. sp<ProcessState>proc=ProcessState::self();
28. if(proc->supportsProcesses()){
29. LOGV("Appprocess:startingthreadpool./n");
30. proc->startThreadPool();
31. }
33. app_init(mClassName,mArgC,mArgV);
35. if(ProcessState::self()->supportsProcesses()){
36. IPCThreadState::self()->stopProcess();
37. }
38. }
40. virtualvoidonZygoteInit()
41. {
42. sp<ProcessState>proc=ProcessState::self();
43. if(proc->supportsProcesses()){
44. LOGV("Appprocess:startingthreadpool./n");
45. proc->startThreadPool();
46. }
47. }
49. virtualvoidonExit(intcode)
50. {
51. if(mClassName==NULL){
52. //ifzygote
53. if(ProcessState::self()->supportsProcesses()){
54. IPCThreadState::self()->stopProcess();
55. }
56. }
58. AndroidRuntime::onExit(code);
59. }
62. constchar*mParentDir;
63. constchar*mClassName;
64. intmArgC;
65. constchar*const*mArgV;
66. };
68. }

class AppRuntime : public AndroidRuntime //基类是AndroidRuntime，待会分析下是干嘛的 { public: AppRuntime() : mParentDir(NULL) , mClassName(NULL) , mArgC(0) , mArgV(NULL) { } #if 0 // this appears to be unused const char* getParentDir() const { return mParentDir; } #endif const char* getClassName() const { return mClassName; } virtual void onStarted() //下面几个onXXX应该是回调用的，可能是JNI回调 { sp<ProcessState> proc = ProcessState::self(); if (proc->supportsProcesses()) { LOGV("App process: starting thread pool./n"); proc->startThreadPool(); } app_init(mClassName, mArgC, mArgV); if (ProcessState::self()->supportsProcesses()) { IPCThreadState::self()->stopProcess(); } } virtual void onZygoteInit() { sp<ProcessState> proc = ProcessState::self(); if (proc->supportsProcesses()) { LOGV("App process: starting thread pool./n"); proc->startThreadPool(); } } virtual void onExit(int code) { if (mClassName == NULL) { // if zygote if (ProcessState::self()->supportsProcesses()) { IPCThreadState::self()->stopProcess(); } } AndroidRuntime::onExit(code); } const char* mParentDir; const char* mClassName; int mArgC; const char* const* mArgV; }; }

其中，基类AndroidRuntime.h在frameworks/base/include/android_runtime/AndroidRuntime.h中定义。大概看看里边都定义了些什么。

[cpp:collapse] + expand source view plain copy print ?

1. namespaceandroid{
2. //这个类是与java虚拟机交互的一个类。
3. //估计java虚拟机由它启动了
4. classAndroidRuntime
5. {
6. public:
7. AndroidRuntime();
8. virtual~AndroidRuntime();
10. /**
11. *Registerasetofmethodsinthespecifiedclass.
12. */
13. staticintregisterNativeMethods(JNIEnv*env,
14. constchar*className,constJNINativeMethod*gMethods,intnumMethods);
16. /**
17. *CallastaticJavafunctionthattakesnoargumentsandreturnsvoid.
18. */
19. status_tcallStatic(constchar*className,constchar*methodName);
21. /**
22. *Callaclass'sstaticmainmethodwiththegivenarguments,
23. */
24. status_tcallMain(constchar*className,intargc,constchar*constargv[]);
26. /**
27. *Findaclass,withtheinputeitheroftheform
28. *"package/class"or"package.class".
29. */
30. staticjclassfindClass(JNIEnv*env,constchar*className);
32. intaddVmArguments(intargc,constchar*constargv[]);
34. voidstart(constchar*classname,constboolstartSystemServer);
35. voidstart();//startinandroid.util.RuntimeInit
37. staticAndroidRuntime*getRuntime();
39. /**
40. *ThisgetscalledaftertheJavaVMhasinitialized.Overrideit
41. *withthesystem'snativeentrypoint.
42. */
43. virtualvoidonStarted()=0;
45. /**
46. *ThisgetscalledaftertheJavaVMhasinitializedafteraZygote
47. *fork.Overrideittoinitializethreads,etc.Uponreturn,the
48. *correctstaticmainwillbeinvoked.
49. */
50. virtualvoidonZygoteInit(){};
53. /**
54. *CalledwhentheJavaapplicationexits.Thedefault
55. *implementationcallsexit(code).
56. */
57. virtualvoidonExit(intcode);
59. /**createanewthreadthatisvisiblefromJava*/
60. staticvoidcreateJavaThread(constchar*name,void(*start)(void*),
61. void*arg);
63. /**returnapointertotheVMrunninginthisprocess*/
64. staticJavaVM*getJavaVM(){returnmJavaVM;}
66. /**returnapointertotheJNIEnvpointerforthisthread*/
67. staticJNIEnv*getJNIEnv();
69. private:
70. staticintstartReg(JNIEnv*env);
71. intstartVm(JavaVM**pJavaVM,JNIEnv**pEnv);
73. Vector<JavaVMOption>mOptions;
75. /*JNIJavaVMpointer*/
76. staticJavaVM*mJavaVM;
78. /*
79. *Threadcreationhelpers.
80. */
81. staticintjavaCreateThreadEtc(
82. android_thread_func_tentryFunction,
83. void*userData,
84. constchar*threadName,
85. int32_tthreadPriority,
86. size_tthreadStackSize,
87. android_thread_id_t*threadId);
88. staticintjavaThreadShell(void*args);
89. };
91. //ReturnstheUnixfiledescriptorforaParcelFileDescriptorobject
92. externintgetParcelFileDescriptorFD(JNIEnv*env,jobjectobject);
94. }

namespace android { //这个类是与java虚拟机交互的一个类。 //估计java虚拟机由它启动了 class AndroidRuntime { public: AndroidRuntime(); virtual ~AndroidRuntime(); /** * Register a set of methods in the specified class. */ static int registerNativeMethods(JNIEnv* env, const char* className, const JNINativeMethod* gMethods, int numMethods); /** * Call a static Java function that takes no arguments and returns void. */ status_t callStatic(const char* className, const char* methodName); /** * Call a class's static main method with the given arguments, */ status_t callMain(const char* className, int argc, const char* const argv[]); /** * Find a class, with the input either of the form * "package/class" or "package.class". */ static jclass findClass(JNIEnv* env, const char* className); int addVmArguments(int argc, const char* const argv[]); void start(const char *classname, const bool startSystemServer); void start(); // start in android.util.RuntimeInit static AndroidRuntime* getRuntime(); /** * This gets called after the JavaVM has initialized. Override it * with the system's native entry point. */ virtual void onStarted() = 0; /** * This gets called after the JavaVM has initialized after a Zygote * fork. Override it to initialize threads, etc. Upon return, the * correct static main will be invoked. */ virtual void onZygoteInit() {}; /** * Called when the Java application exits. The default * implementation calls exit(code). */ virtual void onExit(int code); /** create a new thread that is visible from Java */ static void createJavaThread(const char* name, void (*start)(void *), void* arg); /** return a pointer to the VM running in this process */ static JavaVM* getJavaVM() { return mJavaVM; } /** return a pointer to the JNIEnv pointer for this thread */ static JNIEnv* getJNIEnv(); private: static int startReg(JNIEnv* env); int startVm(JavaVM** pJavaVM, JNIEnv** pEnv); Vector<JavaVMOption> mOptions; /* JNI JavaVM pointer */ static JavaVM* mJavaVM; /* * Thread creation helpers. */ static int javaCreateThreadEtc( android_thread_func_t entryFunction, void* userData, const char* threadName, int32_t threadPriority, size_t threadStackSize, android_thread_id_t* threadId); static int javaThreadShell(void* args); }; // Returns the Unix file descriptor for a ParcelFileDescriptor object extern int getParcelFileDescriptorFD(JNIEnv* env, jobject object); }

AndroidRuntime类主要是和java打交道，而且好像只能由framework调用才能起作用，一般我自己的jni库都不用AndroidRuntime里边定义的方便函数，虽然都是static。原因如下（必须看看它的实现文件才知道原因）

[cpp] view plain copy print ?

1. //看来系统有一个全局的mJavaVM
2. JavaVM*AndroidRuntime::mJavaVM=NULL;
3. //整个系统范围内，第一次调用构造函数的应该就是在app_process中的吧？！
4. AndroidRuntime::AndroidRuntime()
5. {
6. SkGraphics::Init();
7. //thissetsourpreferencefor16bitimagesduringdecode
8. //incasethesrcisopaqueand24bit
9. SkImageDecoder::SetDeviceConfig(SkBitmap::kRGB_565_Config);
10. //Thiscacheissharedbetweenbrowsernativeimages,andjava"purgeable"
11. //bitmaps.Thisglobalpoolisforimagesthatdonoteitherusethejava
12. //heap,orarenotbackedbyashmem.SeeBitmapFactory.cppforthekey
13. //javacallsite.
14. SkImageRef_GlobalPool::SetRAMBudget(512*1024);
15. //Thereisalsoaglobalfontcache,butitsbudgetisspecifiedincode
16. //seeSkFontHost_android.cpp
18. //Pre-allocateenoughspacetoholdafairnumberofoptions.
19. mOptions.setCapacity(20);
21. assert(gCurRuntime==NULL);//oneperprocess
22. gCurRuntime=this;
23. }
24. //刚才那几个onXXX函数就是在这里调用的，估计是java层调用的
25. staticvoidcom_android_internal_os_RuntimeInit_finishInit(JNIEnv*env,jobjectclazz)
26. {
27. gCurRuntime->onStarted();
28. }
30. staticvoidcom_android_internal_os_RuntimeInit_zygoteInit(JNIEnv*env,jobjectclazz)
31. {
32. gCurRuntime->onZygoteInit();
33. }
35. staticjintcom_android_internal_os_RuntimeInit_isComputerOn(JNIEnv*env,jobjectclazz)
36. {
37. return1;
38. }
40. staticvoidcom_android_internal_os_RuntimeInit_turnComputerOn(JNIEnv*env,jobjectclazz)
41. {
42. }
44. staticjintcom_android_internal_os_RuntimeInit_getQwertyKeyboard(JNIEnv*env,jobjectclazz)
45. {
46. char*value=getenv("qwerty");
47. if(value!=NULL&&strcmp(value,"true")==0){
48. return1;
49. }
51. return0;
52. }
53. //略去一些
54. intAndroidRuntime::addVmArguments(intargc,constchar*constargv[])
55. {
56. inti;
58. for(i=0;i<argc;i++){
59. if(argv[i][0]!='-'){
60. returni;
61. }
62. if(argv[i][1]=='-'&&argv[i][2]==0){
63. returni+1;
64. }
65. //此时虚拟机还没有起来，先把这些options保存起来
66. JavaVMOptionopt;
67. memset(&opt,0,sizeof(opt));
68. opt.optionString=(char*)argv[i];
69. mOptions.add(opt);
70. }
71. returni;
72. }

//看来系统有一个全局的mJavaVM JavaVM* AndroidRuntime::mJavaVM = NULL; //整个系统范围内，第一次调用构造函数的应该就是在app_process中的吧？！ AndroidRuntime::AndroidRuntime() { SkGraphics::Init(); // this sets our preference for 16bit images during decode // in case the src is opaque and 24bit SkImageDecoder::SetDeviceConfig(SkBitmap::kRGB_565_Config); // This cache is shared between browser native images, and java "purgeable" // bitmaps. This globalpool is for images that do not either use the java // heap, or are not backed by ashmem. See BitmapFactory.cpp for the key // java call site. SkImageRef_GlobalPool::SetRAMBudget(512 * 1024); // There is also a global font cache, but its budget is specified in code // see SkFontHost_android.cpp // Pre-allocate enough space to hold a fair number of options. mOptions.setCapacity(20); assert(gCurRuntime == NULL); // one per process gCurRuntime = this; } //刚才那几个onXXX函数就是在这里调用的，估计是java层调用的 static void com_android_internal_os_RuntimeInit_finishInit(JNIEnv* env, jobject clazz) { gCurRuntime->onStarted(); } static void com_android_internal_os_RuntimeInit_zygoteInit(JNIEnv* env, jobject clazz) { gCurRuntime->onZygoteInit(); } static jint com_android_internal_os_RuntimeInit_isComputerOn(JNIEnv* env, jobject clazz) { return 1; } static void com_android_internal_os_RuntimeInit_turnComputerOn(JNIEnv* env, jobject clazz) { } static jint com_android_internal_os_RuntimeInit_getQwertyKeyboard(JNIEnv* env, jobject clazz) { char* value = getenv("qwerty"); if (value != NULL && strcmp(value, "true") == 0) { return 1; } return 0; } //略去一些 int AndroidRuntime::addVmArguments(int argc, const char* const argv[]) { int i; for (i = 0; i<argc; i++) { if (argv[i][0] != '-') { return i; } if (argv[i][1] == '-' && argv[i][2] == 0) { return i+1; } //此时虚拟机还没有起来，先把这些options保存起来 JavaVMOption opt; memset(&opt, 0, sizeof(opt)); opt.optionString = (char*)argv[i]; mOptions.add(opt); } return i; }

该cpp位置在/frameworks/base/core/jni/AndroidRuntime.cpp中。

回到app_process的main中，此处已运到到runtime.start("com.android.internal.os.ZygoteInit", startSystemServer)这句话来了，应进去看看start到底干了什么。

说来说去，不如看代码分析。

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