Block学习笔记一之结构探究

Block代码实现探究

#import "stdio.h"

int main()
{
    void (^blk)(void) = ^{
      printf("block/n");
    };

    blk();
    return 0;
};

使用clang命令

clang -rewrite-objc block.m

其中block.m是文件的名字，转换为可读的源代码：block.cpp

block的本质是结构体，基本定义的源码定义如下：

struct __block_impl {
  void *isa;
  int Flags;
  int Reserved;
  void *FuncPtr;
};

我们写的

void (^blk)(void) = ^{
      printf("block/n");
    };

转化成了

//生成对应的结构体声明
struct __main_block_impl_0 {
  struct __block_impl impl;
  struct __main_block_desc_0* Desc;
  
  //构造函数
  __main_block_impl_0(void *fp, struct __main_block_desc_0 *desc, int flags=0) {
     //&_NSConcreteStackBlock block结构体实例
    impl.isa = &_NSConcreteStackBlock;
    impl.Flags = flags;
    impl.FuncPtr = fp;
    Desc = desc;
  }
};
//void 是返回类型 __main_block_func_0是函数名称 *__cself是参数 这里相当于self
// 这个是block里面的方法实现
static void __main_block_func_0(struct __main_block_impl_0 *__cself) {

      printf("block/n");
    }

//根据__main_block_impl_0的大小进行初始化
static struct __main_block_desc_0 {
  size_t reserved;
  size_t Block_size;
} __main_block_desc_0_DATA = { 0, sizeof(struct __main_block_impl_0)};

整个main函数转化为：

int main()
{
    //使用__main_block_impl_0的构造函数 生成结构体对象并将指针赋值给blk
    void (*blk)(void) = ((void (*)())&__main_block_impl_0((void *)__main_block_func_0, &__main_block_desc_0_DATA));
    //blk的调用 除去类型转换简化为 
    // (*blk->impl.FuncPtr)(blk);
    ((void (*)(__block_impl *))((__block_impl *)blk)->FuncPtr)((__block_impl *)blk);
    return 0;
};

Block和Objective-C中类的实现原理基本一致，都是使用结构体。

下面是一个基于objc_class的class_t的结构体样式。

struct class_t{
        struct class_t *isa;
        struct class_t *superclass;
        Cache cache;
        IMP *vtable;
        uintptr_t data_NEVER_USE;
}

Block其实和其他类实现一样，是Objective-C的对象。

附录

clang解析的完整代码（有点多）有兴趣的朋友可以按上面的clang命令自己解析看看。

#ifndef __OBJC2__
#define __OBJC2__
#endif
struct objc_selector; struct objc_class;
struct __rw_objc_super { 
    struct objc_object *object; 
    struct objc_object *superClass; 
    __rw_objc_super(struct objc_object *o, struct objc_object *s) : object(o), superClass(s) {} 
};
#ifndef _REWRITER_typedef_Protocol
typedef struct objc_object Protocol;
#define _REWRITER_typedef_Protocol
#endif
#define __OBJC_RW_DLLIMPORT extern
__OBJC_RW_DLLIMPORT void objc_msgSend(void);
__OBJC_RW_DLLIMPORT void objc_msgSendSuper(void);
__OBJC_RW_DLLIMPORT void objc_msgSend_stret(void);
__OBJC_RW_DLLIMPORT void objc_msgSendSuper_stret(void);
__OBJC_RW_DLLIMPORT void objc_msgSend_fpret(void);
__OBJC_RW_DLLIMPORT struct objc_class *objc_getClass(const char *);
__OBJC_RW_DLLIMPORT struct objc_class *class_getSuperclass(struct objc_class *);
__OBJC_RW_DLLIMPORT struct objc_class *objc_getMetaClass(const char *);
__OBJC_RW_DLLIMPORT void objc_exception_throw( struct objc_object *);
__OBJC_RW_DLLIMPORT int objc_sync_enter( struct objc_object *);
__OBJC_RW_DLLIMPORT int objc_sync_exit( struct objc_object *);
__OBJC_RW_DLLIMPORT Protocol *objc_getProtocol(const char *);
#ifdef _WIN64
typedef unsigned long long  _WIN_NSUInteger;
#else
typedef unsigned int _WIN_NSUInteger;
#endif
#ifndef __FASTENUMERATIONSTATE
struct __objcFastEnumerationState {
    unsigned long state;
    void **itemsPtr;
    unsigned long *mutationsPtr;
    unsigned long extra[5];
};
__OBJC_RW_DLLIMPORT void objc_enumerationMutation(struct objc_object *);
#define __FASTENUMERATIONSTATE
#endif
#ifndef __NSCONSTANTSTRINGIMPL
struct __NSConstantStringImpl {
  int *isa;
  int flags;
  char *str;
#if _WIN64
  long long length;
#else
  long length;
#endif
};
#ifdef CF_EXPORT_CONSTANT_STRING
extern "C" __declspec(dllexport) int __CFConstantStringClassReference[];
#else
__OBJC_RW_DLLIMPORT int __CFConstantStringClassReference[];
#endif
#define __NSCONSTANTSTRINGIMPL
#endif
#ifndef BLOCK_IMPL
#define BLOCK_IMPL
struct __block_impl {
  void *isa;
  int Flags;
  int Reserved;
  void *FuncPtr;
};
// Runtime copy/destroy helper functions (from Block_private.h)
#ifdef __OBJC_EXPORT_BLOCKS
extern "C" __declspec(dllexport) void _Block_object_assign(void *, const void *, const int);
extern "C" __declspec(dllexport) void _Block_object_dispose(const void *, const int);
extern "C" __declspec(dllexport) void *_NSConcreteGlobalBlock[32];
extern "C" __declspec(dllexport) void *_NSConcreteStackBlock[32];
#else
__OBJC_RW_DLLIMPORT void _Block_object_assign(void *, const void *, const int);
__OBJC_RW_DLLIMPORT void _Block_object_dispose(const void *, const int);
__OBJC_RW_DLLIMPORT void *_NSConcreteGlobalBlock[32];
__OBJC_RW_DLLIMPORT void *_NSConcreteStackBlock[32];
#endif
#endif
#define __block
#define __weak

#include <stdarg.h>
struct __NSContainer_literal {
  void * *arr;
  __NSContainer_literal (unsigned int count, ...) {
    va_list marker;
    va_start(marker, count);
    arr = new void *[count];
    for (unsigned i = 0; i < count; i++)
      arr[i] = va_arg(marker, void *);
    va_end( marker );
  };
  ~__NSContainer_literal() {
    delete[] arr;
  }
};
extern "C" __declspec(dllimport) void * objc_autoreleasePoolPush(void);
extern "C" __declspec(dllimport) void objc_autoreleasePoolPop(void *);

struct __AtAutoreleasePool {
  __AtAutoreleasePool() {atautoreleasepoolobj = objc_autoreleasePoolPush();}
  ~__AtAutoreleasePool() {objc_autoreleasePoolPop(atautoreleasepoolobj);}
  void * atautoreleasepoolobj;
};

#define __OFFSETOFIVAR__(TYPE, MEMBER) ((long long) &((TYPE *)0)->MEMBER)

typedef signed char __int8_t;



typedef unsigned char __uint8_t;
typedef short __int16_t;
typedef unsigned short __uint16_t;
typedef int __int32_t;
typedef unsigned int __uint32_t;
typedef long long __int64_t;
typedef unsigned long long __uint64_t;

typedef long __darwin_intptr_t;
typedef unsigned int __darwin_natural_t;
typedef int __darwin_ct_rune_t;





typedef union {
 char __mbstate8[128];
 long long _mbstateL;
} __mbstate_t;

typedef __mbstate_t __darwin_mbstate_t;


typedef long int __darwin_ptrdiff_t;







typedef long unsigned int __darwin_size_t;





typedef __builtin_va_list __darwin_va_list;





typedef int __darwin_wchar_t;




typedef __darwin_wchar_t __darwin_rune_t;


typedef int __darwin_wint_t;




typedef unsigned long __darwin_clock_t;
typedef __uint32_t __darwin_socklen_t;
typedef long __darwin_ssize_t;
typedef long __darwin_time_t;
typedef __int64_t __darwin_blkcnt_t;
typedef __int32_t __darwin_blksize_t;
typedef __int32_t __darwin_dev_t;
typedef unsigned int __darwin_fsblkcnt_t;
typedef unsigned int __darwin_fsfilcnt_t;
typedef __uint32_t __darwin_gid_t;
typedef __uint32_t __darwin_id_t;
typedef __uint64_t __darwin_ino64_t;

typedef __darwin_ino64_t __darwin_ino_t;



typedef __darwin_natural_t __darwin_mach_port_name_t;
typedef __darwin_mach_port_name_t __darwin_mach_port_t;
typedef __uint16_t __darwin_mode_t;
typedef __int64_t __darwin_off_t;
typedef __int32_t __darwin_pid_t;
typedef __uint32_t __darwin_sigset_t;
typedef __int32_t __darwin_suseconds_t;
typedef __uint32_t __darwin_uid_t;
typedef __uint32_t __darwin_useconds_t;
typedef unsigned char __darwin_uuid_t[16];
typedef char __darwin_uuid_string_t[37];


struct __darwin_pthread_handler_rec {
 void (*__routine)(void *);
 void *__arg;
 struct __darwin_pthread_handler_rec *__next;
};

struct _opaque_pthread_attr_t {
 long __sig;
 char __opaque[56];
};

struct _opaque_pthread_cond_t {
 long __sig;
 char __opaque[40];
};

struct _opaque_pthread_condattr_t {
 long __sig;
 char __opaque[8];
};

struct _opaque_pthread_mutex_t {
 long __sig;
 char __opaque[56];
};

struct _opaque_pthread_mutexattr_t {
 long __sig;
 char __opaque[8];
};

struct _opaque_pthread_once_t {
 long __sig;
 char __opaque[8];
};

struct _opaque_pthread_rwlock_t {
 long __sig;
 char __opaque[192];
};

struct _opaque_pthread_rwlockattr_t {
 long __sig;
 char __opaque[16];
};

struct _opaque_pthread_t {
 long __sig;
 struct __darwin_pthread_handler_rec *__cleanup_stack;
 char __opaque[8176];
};

typedef struct _opaque_pthread_attr_t __darwin_pthread_attr_t;
typedef struct _opaque_pthread_cond_t __darwin_pthread_cond_t;
typedef struct _opaque_pthread_condattr_t __darwin_pthread_condattr_t;
typedef unsigned long __darwin_pthread_key_t;
typedef struct _opaque_pthread_mutex_t __darwin_pthread_mutex_t;
typedef struct _opaque_pthread_mutexattr_t __darwin_pthread_mutexattr_t;
typedef struct _opaque_pthread_once_t __darwin_pthread_once_t;
typedef struct _opaque_pthread_rwlock_t __darwin_pthread_rwlock_t;
typedef struct _opaque_pthread_rwlockattr_t __darwin_pthread_rwlockattr_t;
typedef struct _opaque_pthread_t *__darwin_pthread_t;
typedef int __darwin_nl_item;
typedef int __darwin_wctrans_t;

typedef __uint32_t __darwin_wctype_t;



typedef __darwin_va_list va_list;
typedef __darwin_size_t size_t;

extern "C" {

int renameat(int, const char *, int, const char *) __attribute__((availability(macosx,introduced=10.10)));






int renamex_np(const char *, const char *, unsigned int) __attribute__((availability(macosx,introduced=10.12))) __attribute__((availability(ios,introduced=10.0))) __attribute__((availability(tvos,introduced=10.0))) __attribute__((availability(watchos,introduced=3.0)));
int renameatx_np(int, const char *, int, const char *, unsigned int) __attribute__((availability(macosx,introduced=10.12))) __attribute__((availability(ios,introduced=10.0))) __attribute__((availability(tvos,introduced=10.0))) __attribute__((availability(watchos,introduced=3.0)));



}

typedef __darwin_off_t fpos_t;
struct __sbuf {
 unsigned char *_base;
 int _size;
};


struct __sFILEX;
typedef struct __sFILE {
 unsigned char *_p;
 int _r;
 int _w;
 short _flags;
 short _file;
 struct __sbuf _bf;
 int _lbfsize;


 void *_cookie;
 int (* _Nullable _close)(void *);
 int (* _Nullable _read) (void *, char *, int);
 fpos_t (* _Nullable _seek) (void *, fpos_t, int);
 int (* _Nullable _write)(void *, const char *, int);


 struct __sbuf _ub;
 struct __sFILEX *_extra;
 int _ur;


 unsigned char _ubuf[3];
 unsigned char _nbuf[1];


 struct __sbuf _lb;


 int _blksize;
 fpos_t _offset;
} FILE;

extern "C" {
extern FILE *__stdinp;
extern FILE *__stdoutp;
extern FILE *__stderrp;
}
extern "C" {
void clearerr(FILE *);
int fclose(FILE *);
int feof(FILE *);
int ferror(FILE *);
int fflush(FILE *);
int fgetc(FILE *);
int fgetpos(FILE * , fpos_t *);
char *fgets(char * , int, FILE *);



FILE *fopen(const char * __filename, const char * __mode) __asm("_" "fopen" );

int fprintf(FILE * , const char * , ...) __attribute__((__format__ (__printf__, 2, 3)));
int fputc(int, FILE *);
int fputs(const char * , FILE * ) __asm("_" "fputs" );
size_t fread(void * __ptr, size_t __size, size_t __nitems, FILE * __stream);
FILE *freopen(const char * , const char * ,
                 FILE * ) __asm("_" "freopen" );
int fscanf(FILE * , const char * , ...) __attribute__((__format__ (__scanf__, 2, 3)));
int fseek(FILE *, long, int);
int fsetpos(FILE *, const fpos_t *);
long ftell(FILE *);
size_t fwrite(const void * __ptr, size_t __size, size_t __nitems, FILE * __stream) __asm("_" "fwrite" );
int getc(FILE *);
int getchar(void);
char *gets(char *);
void perror(const char *);
int printf(const char * , ...) __attribute__((__format__ (__printf__, 1, 2)));
int putc(int, FILE *);
int putchar(int);
int puts(const char *);
int remove(const char *);
int rename (const char *__old, const char *__new);
void rewind(FILE *);
int scanf(const char * , ...) __attribute__((__format__ (__scanf__, 1, 2)));
void setbuf(FILE * , char * );
int setvbuf(FILE * , char * , int, size_t);
int sprintf(char * , const char * , ...) __attribute__((__format__ (__printf__, 2, 3))) __attribute__((__availability__(swift, unavailable, message="Use snprintf instead.")));
int sscanf(const char * , const char * , ...) __attribute__((__format__ (__scanf__, 2, 3)));
FILE *tmpfile(void);

__attribute__((__availability__(swift, unavailable, message="Use mkstemp(3) instead.")))

__attribute__((deprecated("This function is provided for compatibility reasons only.  Due to security concerns inherent in the design of tmpnam(3), it is highly recommended that you use mkstemp(3) instead.")))

char *tmpnam(char *);
int ungetc(int, FILE *);
int vfprintf(FILE * , const char * , va_list) __attribute__((__format__ (__printf__, 2, 0)));
int vprintf(const char * , va_list) __attribute__((__format__ (__printf__, 1, 0)));
int vsprintf(char * , const char * , va_list) __attribute__((__format__ (__printf__, 2, 0))) __attribute__((__availability__(swift, unavailable, message="Use vsnprintf instead.")));
}
extern "C" {



char *ctermid(char *);





FILE *fdopen(int, const char *) __asm("_" "fdopen" );

int fileno(FILE *);
}
extern "C" {
int pclose(FILE *) __attribute__((__availability__(swift, unavailable, message="Use posix_spawn APIs or NSTask instead.")));



FILE *popen(const char *, const char *) __asm("_" "popen" ) __attribute__((__availability__(swift, unavailable, message="Use posix_spawn APIs or NSTask instead.")));

}
extern "C" {
int __srget(FILE *);
int __svfscanf(FILE *, const char *, va_list) __attribute__((__format__ (__scanf__, 2, 0)));
int __swbuf(int, FILE *);
}







inline __attribute__ ((__always_inline__)) int __sputc(int _c, FILE *_p) {
 if (--_p->_w >= 0 || (_p->_w >= _p->_lbfsize && (char)_c != '\n'))
  return (*_p->_p++ = _c);
 else
  return (__swbuf(_c, _p));
}
extern "C" {
void flockfile(FILE *);
int ftrylockfile(FILE *);
void funlockfile(FILE *);
int getc_unlocked(FILE *);
int getchar_unlocked(void);
int putc_unlocked(int, FILE *);
int putchar_unlocked(int);



int getw(FILE *);
int putw(int, FILE *);


__attribute__((__availability__(swift, unavailable, message="Use mkstemp(3) instead.")))

__attribute__((deprecated("This function is provided for compatibility reasons only.  Due to security concerns inherent in the design of tempnam(3), it is highly recommended that you use mkstemp(3) instead.")))

char *tempnam(const char *__dir, const char *__prefix) __asm("_" "tempnam" );
}
typedef __darwin_off_t off_t;

extern "C" {
int fseeko(FILE * __stream, off_t __offset, int __whence);
off_t ftello(FILE * __stream);
}



extern "C" {
int snprintf(char * __str, size_t __size, const char * __format, ...) __attribute__((__format__ (__printf__, 3, 4)));
int vfscanf(FILE * __stream, const char * __format, va_list) __attribute__((__format__ (__scanf__, 2, 0)));
int vscanf(const char * __format, va_list) __attribute__((__format__ (__scanf__, 1, 0)));
int vsnprintf(char * __str, size_t __size, const char * __format, va_list) __attribute__((__format__ (__printf__, 3, 0)));
int vsscanf(const char * __str, const char * __format, va_list) __attribute__((__format__ (__scanf__, 2, 0)));
}
typedef __darwin_ssize_t ssize_t;

extern "C" {
int dprintf(int, const char * , ...) __attribute__((__format__ (__printf__, 2, 3))) __attribute__((availability(macosx,introduced=10.7)));
int vdprintf(int, const char * , va_list) __attribute__((__format__ (__printf__, 2, 0))) __attribute__((availability(macosx,introduced=10.7)));
ssize_t getdelim(char ** __linep, size_t * __linecapp, int __delimiter, FILE * __stream) __attribute__((availability(macosx,introduced=10.7)));
ssize_t getline(char ** __linep, size_t * __linecapp, FILE * __stream) __attribute__((availability(macosx,introduced=10.7)));
}







extern "C" {
extern const int sys_nerr;
extern const char *const sys_errlist[];

int asprintf(char ** , const char * , ...) __attribute__((__format__ (__printf__, 2, 3)));
char *ctermid_r(char *);
char *fgetln(FILE *, size_t *);
const char *fmtcheck(const char *, const char *);
int fpurge(FILE *);
void setbuffer(FILE *, char *, int);
int setlinebuf(FILE *);
int vasprintf(char ** , const char * , va_list) __attribute__((__format__ (__printf__, 2, 0)));
FILE *zopen(const char *, const char *, int);





FILE *funopen(const void *,
                 int (* _Nullable)(void *, char *, int),
                 int (* _Nullable)(void *, const char *, int),
                 fpos_t (* _Nullable)(void *, fpos_t, int),
                 int (* _Nullable)(void *));
}


struct __main_block_impl_0 {
  struct __block_impl impl;
  struct __main_block_desc_0* Desc;
  __main_block_impl_0(void *fp, struct __main_block_desc_0 *desc, int flags=0) {
    impl.isa = &_NSConcreteStackBlock;
    impl.Flags = flags;
    impl.FuncPtr = fp;
    Desc = desc;
  }
};
static void __main_block_func_0(struct __main_block_impl_0 *__cself) {

      printf("block/n");
    }

static struct __main_block_desc_0 {
  size_t reserved;
  size_t Block_size;
} __main_block_desc_0_DATA = { 0, sizeof(struct __main_block_impl_0)};
int main()
{
    void (*blk)(void) = ((void (*)())&__main_block_impl_0((void *)__main_block_func_0, &__main_block_desc_0_DATA));

    ((void (*)(__block_impl *))((__block_impl *)blk)->FuncPtr)((__block_impl *)blk);
    return 0;
};
static struct IMAGE_INFO { unsigned version; unsigned flag; } _OBJC_IMAGE_INFO = { 0, 2 };