开场白
Block基本概念
中间态转换方法
Block编译后结果分析
Block运行时状态与编译状态对比
开场白
Object-C语言是对C语言的扩展，所以将OC源码进行编译的时候，会将OC源码会被转换成C\C++，所以想了解OC源码的实现细节，还是需要手动编译成中间状态进行观察。
命令1:
clang -rewrite-objc main.m
如果Xcode版本较高，可能会出现报错：
./block_VC.h::: fatal error: 'UIKit/UIKit.h' file not found
此时可尝试另一个命令：
clang -x objective-c -rewrite-objc -isysroot /Applications/Xcode.app/Contents/Developer/Platforms/iPhoneSimulator.platform/Developer/SDKs/iPhoneSimulator.sdk main.m
命令好长，每次输入这么长的指令很麻烦，此时可以考虑使用命令别名：alias
Block的基本概念
_NSConcreteGlobalBlock 全局的静态 block，不会访问任何外部变量。
_NSConcreteStackBlock 保存在栈中的 block，当函数返回时会被销毁。
_NSConcreteMallocBlock 保存在堆中的 block，当引用计数为 0 时会被销毁。
堆中的 block何时转换：
1.调用copy方法时
2.从一个函数返回时
3.将block传入dispatch等系统IPA参数block或者传递给带有usingBlock的Cocoa框架函数时。
4.将block赋给带有__strong修饰符的id类型或者Block类型时。
Block类型变换方式
1.没有捕获任何局部变量的block为_NSConcreteGlobalBlock，它以static函数的形式存储在代码区
2.捕获了局部变量的block为_NSConcreteStackBlock
3.当_NSConcreteStackBlock出现上面四种情况时，会变成_NSConcreteMallocBlock。（注意此时是调用了Block_Copy函数后）
Block编译后结果分析
基本类型变量
OC源码：
NSInteger age = ;
void(^completeBlock)(NSString *) = ^(NSString *name) {
NSString *info = [NSString stringWithFormat:@"name:%@ - age:%d",name,age];
NSLog(@"%@",info);
}; completeBlock(@"jack");
编译后的C\C++源码：
// __block_impl为block的基础struct
//1.*isa：当前block对象所属的类型（注意：在OC语言中带有isa指针的都是对象）
//2.Flags：标示位，当类型为NSConcreteMallocBlock时，表示需要ARC内存管理，其他默认不需要内存管理
//3.Reserved：预留标示位，暂时不管它
//4.block的实际static内部函数地址指针
struct __block_impl {
void *isa;
int Flags;
int Reserved;
void *FuncPtr;
}; // __main_block_impl_0为block的最终struct
//1.impl：为上面的__block_impl结构体实例
//2.Desc：为block的描述结构体__main_block_desc_0，里面包含了block结构体的信息描述，在下面讲解
//3.age：从外面补货的变量，block采用的方式是直接在block实例中定义一个变量，将捕获的值赋给它
//4.__main_block_impl_0：为block结构体的构造函数，参数中包含从外面捕获的变量值
struct __main_block_impl_0 {
struct __block_impl impl;
struct __main_block_desc_0* Desc;
NSInteger age;
__main_block_impl_0(void *fp, struct __main_block_desc_0 *desc, NSInteger _age, int flags=) : age(_age) {
impl.isa = &_NSConcreteStackBlock;
impl.Flags = flags;
impl.FuncPtr = fp;
Desc = desc;
}
}; //__main_block_func_0为block具体实现的函数载体，具体的block的任务实现在此函数内
//参数：1是block的实例指针，2是block的外部传参name
static void __main_block_func_0(struct __main_block_impl_0 *__cself, NSString *name) {
//从block实例中获取age变量的值
NSInteger age = __cself->age; // bound by copy //生成字符串NSString *info = [NSString stringWithFormat:@"name:%@ - age:%d",name,age];
NSString *info = ((NSString * _Nonnull (*)(id, SEL, NSString * _Nonnull, ...))(void *)objc_msgSend)((id)objc_getClass("NSString"), sel_registerName("stringWithFormat:"), (NSString *)&__NSConstantStringImpl__var_folders_4y_ks8945f50k51_0j95ytw7ss80000gn_T_main_83d55e_mi_0, (NSString *)name, (NSInteger)age); //打印NSLog(@"%@",info);
NSLog((NSString *)&__NSConstantStringImpl__var_folders_4y_ks8945f50k51_0j95ytw7ss80000gn_T_main_83d55e_mi_1,info);
} //reserved：保留字0
//Block_size:block实例在内存中占据内存大小
//__main_block_desc_0_DATA：默认desc结构体实例
static struct __main_block_desc_0 {
size_t reserved;
size_t Block_size;
} __main_block_desc_0_DATA = { , sizeof(struct __main_block_impl_0)}; //main函数
int main(int argc, char * argv[]) {
/* @autoreleasepool */ { __AtAutoreleasePool __autoreleasepool; NSInteger age = ;
void(*completeBlock)(NSString *) = ((void (*)(NSString *))&__main_block_impl_0((void *)__main_block_func_0, &__main_block_desc_0_DATA, age)); ((void (*)(__block_impl *, NSString *))((__block_impl *)completeBlock)->FuncPtr)((__block_impl *)completeBlock, (NSString *)&__NSConstantStringImpl__var_folders_4y_ks8945f50k51_0j95ytw7ss80000gn_T_main_83d55e_mi_2); return UIApplicationMain(argc, argv, __null, NSStringFromClass(((Class (*)(id, SEL))(void *)objc_msgSend)((id)objc_getClass("AppDelegate"), sel_registerName("class"))));
}
}
block简单结构布局
struct __block_impl
struct __main_block_impl_0
static void __main_block_func_0
static struct __main_block_desc_0
详细解释见上面的中间编译状态。
block实例中定义了一个age变量，并将外部的age传了过去
__block基本类型变量
OC源码：
__block NSInteger age = ;
void(^completeBlock)(NSString *) = ^(NSString *name) {
NSString *info = [NSString stringWithFormat:@"name:%@ - age:%d",name,age];
NSLog(@"%@",info);
}; completeBlock(@"jack");
编译后的C\C++源码：
struct __block_impl {
void *isa;
int Flags;
int Reserved;
void *FuncPtr;
};
//age的block变量实例__Block_byref_age
//__isa：age的block变量实例所属的类型
//__forwarding：age的block变量实例的指针
//__flags：变量是否被内存管理标示
//__size:所占内存大小
//age:age变量值
struct __Block_byref_age_0 {
void *__isa;
__Block_byref_age_0 *__forwarding;
int __flags;
int __size;
NSInteger age;
};
//原来的age变量值，变成了__Block_byref_age_0变量指针
struct __main_block_impl_0 {
struct __block_impl impl;
struct __main_block_desc_0* Desc;
__Block_byref_age_0 *age; // by ref
__main_block_impl_0(void *fp, struct __main_block_desc_0 *desc, __Block_byref_age_0 *_age, int flags=) : age(_age->__forwarding) {
impl.isa = &_NSConcreteStackBlock;
impl.Flags = flags;
impl.FuncPtr = fp;
Desc = desc;
}
};
static void __main_block_func_0(struct __main_block_impl_0 *__cself, NSString *name) {
//通过block实例获取变量的指针
__Block_byref_age_0 *age = __cself->age; // bound by ref
NSLog((NSString *)&__NSConstantStringImpl__var_folders_4y_ks8945f50k51_0j95ytw7ss80000gn_T_main_7acc63_mi_0,name,(age->__forwarding->age));
}
//当block从栈复制到堆上时，会对__Block_byref_age_0变量进行拷贝，也会从栈拷贝到堆上
static void __main_block_copy_0(struct __main_block_impl_0*dst, struct __main_block_impl_0*src) {_Block_object_assign((void*)&dst->age, (void*)src->age, /*BLOCK_FIELD_IS_BYREF*/);}
//__Block_byref_age_0变量的析构函数，当block实例的引用计数为0时，是否__Block_byref_age_0变量的内存空间
static void __main_block_dispose_0(struct __main_block_impl_0*src) {_Block_object_dispose((void*)src->age, /*BLOCK_FIELD_IS_BYREF*/);}
//desc结构体中新增了copy函数和dispose函数指针
static struct __main_block_desc_0 {
size_t reserved;
size_t Block_size;
void (*copy)(struct __main_block_impl_0*, struct __main_block_impl_0*);
void (*dispose)(struct __main_block_impl_0*);
} __main_block_desc_0_DATA = { , sizeof(struct __main_block_impl_0), __main_block_copy_0, __main_block_dispose_0};
int main(int argc, char * argv[]) {
/* @autoreleasepool */ { __AtAutoreleasePool __autoreleasepool;
//block变量实例
__attribute__((__blocks__(byref))) __Block_byref_age_0 age = {(void*),(__Block_byref_age_0 *)&age, , sizeof(__Block_byref_age_0), };
//block实例
void(*completeBlock)(NSString *) = ((void (*)(NSString *))&__main_block_impl_0((void *)__main_block_func_0, &__main_block_desc_0_DATA, (__Block_byref_age_0 *)&age, ));
((void (*)(__block_impl *, NSString *))((__block_impl *)completeBlock)->FuncPtr)((__block_impl *)completeBlock, (NSString *)&__NSConstantStringImpl__var_folders_4y_ks8945f50k51_0j95ytw7ss80000gn_T_main_7acc63_mi_1);
return UIApplicationMain(argc, argv, __null, NSStringFromClass(((Class (*)(id, SEL))(void *)objc_msgSend)((id)objc_getClass("AppDelegate"), sel_registerName("class"))));
}
}
简单结构布局
struct __block_impl
struct __main_block_impl_0
static void __main_block_func_0
static struct __main_block_desc_0
//新增
struct __Block_byref_age_0
static void __main_block_copy_0(
static void __main_block_dispose_0(
__block NSInteger age = 10;后，在简单布局结构中新增了3项
struct __Block_byref_age_0
static void __main_block_copy_0(
static void __main_block_dispose_0(
__Block_byref_age_0将基本变量转换成__block变量结构体实例指针
__main_block_copy_0和__main_block_dispose_0是对__block变量结构体实例的内存管理方法。
__block变量结构体实例从栈拷贝到堆时，调用方法：__main_block_copy_0
__block变量结构体实例引用计数为0时，调用方法：__main_block_dispose_0
指针类型变量
OC源码：
NSMutableArray *friends = [NSMutableArray array];;
void(^completeBlock)(NSString *) = ^(NSString *name) {
NSLog(@"%@--%@",name,friends);
}; completeBlock(@"jack");
编译后的C\C++源码：
struct __block_impl {
void *isa;
int Flags;
int Reserved;
void *FuncPtr;
};
struct __main_block_impl_0 {
struct __block_impl impl;
struct __main_block_desc_0* Desc;
NSMutableArray *friends;
__main_block_impl_0(void *fp, struct __main_block_desc_0 *desc, NSMutableArray *_friends, int flags=) : friends(_friends) {
impl.isa = &_NSConcreteStackBlock;
impl.Flags = flags;
impl.FuncPtr = fp;
Desc = desc;
}
};
static void __main_block_func_0(struct __main_block_impl_0 *__cself, NSString *name) {
NSMutableArray *friends = __cself->friends; // bound by copy
NSLog((NSString *)&__NSConstantStringImpl__var_folders_4y_ks8945f50k51_0j95ytw7ss80000gn_T_main_1b4a2f_mi_0,name,friends);
}
//block实例从栈复制到堆上时，将指针变量引用计数加一
static void __main_block_copy_0(struct __main_block_impl_0*dst, struct __main_block_impl_0*src) {_Block_object_assign((void*)&dst->friends, (void*)src->friends, /*BLOCK_FIELD_IS_OBJECT*/);}
//block实例引用计数为0时，析构指针变量对象
static void __main_block_dispose_0(struct __main_block_impl_0*src) {_Block_object_dispose((void*)src->friends, /*BLOCK_FIELD_IS_OBJECT*/);}
static struct __main_block_desc_0 {
size_t reserved;
size_t Block_size;
void (*copy)(struct __main_block_impl_0*, struct __main_block_impl_0*);
void (*dispose)(struct __main_block_impl_0*);
} __main_block_desc_0_DATA = { , sizeof(struct __main_block_impl_0), __main_block_copy_0, __main_block_dispose_0};
int main(int argc, char * argv[]) {
/* @autoreleasepool */ { __AtAutoreleasePool __autoreleasepool;
NSMutableArray *friends = ((NSMutableArray * _Nonnull (*)(id, SEL))(void *)objc_msgSend)((id)objc_getClass("NSMutableArray"), sel_registerName("array"));;
void(*completeBlock)(NSString *) = ((void (*)(NSString *))&__main_block_impl_0((void *)__main_block_func_0, &__main_block_desc_0_DATA, friends, ));
((void (*)(__block_impl *, NSString *))((__block_impl *)completeBlock)->FuncPtr)((__block_impl *)completeBlock, (NSString *)&__NSConstantStringImpl__var_folders_4y_ks8945f50k51_0j95ytw7ss80000gn_T_main_1b4a2f_mi_1);
return UIApplicationMain(argc, argv, __null, NSStringFromClass(((Class (*)(id, SEL))(void *)objc_msgSend)((id)objc_getClass("AppDelegate"), sel_registerName("class"))));
}
}
简单结构布局
struct __block_impl
struct __main_block_impl_0
static void __main_block_func_0
static struct __main_block_desc_0
static void __main_block_copy_0(
static void __main_block_dispose_0(
block实例中定义了一个NSMutableArray *friends;指针变量，并通过构造函数将指针传递给block实例
__main_block_copy_0：block实例从栈复制到堆上时，将指针变量引用计数加一
__main_block_dispose_0：block实例引用计数为0时，析构指针变量对象
__block指针类型变量
OC源码：
__block NSMutableArray *friends = [NSMutableArray array];;
void(^completeBlock)(NSString *) = ^(NSString *name) {
NSLog(@"%@--%@",name,friends);
}; completeBlock(@"jack");
编译后的C\C++源码：
struct __block_impl {
void *isa;
int Flags;
int Reserved;
void *FuncPtr;
};
//__Block_byref_friends_0结构体实例中包含了friends指针
//并且多了__Block_byref_id_object_copy函数：对friends进行copy
//多了__Block_byref_id_object_dispose函数：对friends进行析构
struct __Block_byref_friends_0 {
void *__isa;
__Block_byref_friends_0 *__forwarding;
int __flags;
int __size;
void (*__Block_byref_id_object_copy)(void*, void*);
void (*__Block_byref_id_object_dispose)(void*);
NSMutableArray *friends;
};
struct __main_block_impl_0 {
struct __block_impl impl;
struct __main_block_desc_0* Desc;
__Block_byref_friends_0 *friends; // by ref
__main_block_impl_0(void *fp, struct __main_block_desc_0 *desc, __Block_byref_friends_0 *_friends, int flags=) : friends(_friends->__forwarding) {
impl.isa = &_NSConcreteStackBlock;
impl.Flags = flags;
impl.FuncPtr = fp;
Desc = desc;
}
};
static void __main_block_func_0(struct __main_block_impl_0 *__cself, NSString *name) {
__Block_byref_friends_0 *friends = __cself->friends; // bound by ref
NSLog((NSString *)&__NSConstantStringImpl__var_folders_4y_ks8945f50k51_0j95ytw7ss80000gn_T_main_252d0c_mi_0,name,(friends->__forwarding->friends));
}
//block实例从栈复制到堆上时，__block变量结构体实例将指针变量引用计数加一，同时__block变量结构体实例内的NSMutableArray *friends变量也递归加一
static void __main_block_copy_0(struct __main_block_impl_0*dst, struct __main_block_impl_0*src) {_Block_object_assign((void*)&dst->friends, (void*)src->friends, /*BLOCK_FIELD_IS_BYREF*/);}
//block实例引用计数为0时，__block变量结构体实例被析构，同时__block变量结构体实例内的NSMutableArray *friends变量也递归析构
static void __main_block_dispose_0(struct __main_block_impl_0*src) {_Block_object_dispose((void*)src->friends, /*BLOCK_FIELD_IS_BYREF*/);}
static struct __main_block_desc_0 {
size_t reserved;
size_t Block_size;
void (*copy)(struct __main_block_impl_0*, struct __main_block_impl_0*);
void (*dispose)(struct __main_block_impl_0*);
} __main_block_desc_0_DATA = { , sizeof(struct __main_block_impl_0), __main_block_copy_0, __main_block_dispose_0};
int main(int argc, char * argv[]) {
/* @autoreleasepool */ { __AtAutoreleasePool __autoreleasepool;
__attribute__((__blocks__(byref))) __Block_byref_friends_0 friends = {(void*),(__Block_byref_friends_0 *)&friends, , sizeof(__Block_byref_friends_0), __Block_byref_id_object_copy_131, __Block_byref_id_object_dispose_131, ((NSMutableArray * _Nonnull (*)(id, SEL))(void *)objc_msgSend)((id)objc_getClass("NSMutableArray"), sel_registerName("array"))};;
void(*completeBlock)(NSString *) = ((void (*)(NSString *))&__main_block_impl_0((void *)__main_block_func_0, &__main_block_desc_0_DATA, (__Block_byref_friends_0 *)&friends, ));
((void (*)(__block_impl *, NSString *))((__block_impl *)completeBlock)->FuncPtr)((__block_impl *)completeBlock, (NSString *)&__NSConstantStringImpl__var_folders_4y_ks8945f50k51_0j95ytw7ss80000gn_T_main_252d0c_mi_1);
return UIApplicationMain(argc, argv, __null, NSStringFromClass(((Class (*)(id, SEL))(void *)objc_msgSend)((id)objc_getClass("AppDelegate"), sel_registerName("class"))));
}
}
简单结构变量
struct __block_impl
struct __main_block_impl_0
static void __main_block_func_0
static struct __main_block_desc_0
static void __main_block_copy_0(
static void __main_block_dispose_0(
//新增
struct __Block_byref_age_0
和__block普通变量一样，出现了__Block_byref_age_0结构体
__Block_byref_friends_0结构体实例中包含了friends指针
并且多了__Block_byref_id_object_copy函数：对friends进行copy
多了__Block_byref_id_object_dispose函数：对friends进行析构
同时在函数__main_block_copy_0和__main_block_dispose_0中，出现的也是对__Block_byref_age_0结构体的调用。它是在将__Block_byref_age_0结构体析构之前，先析构friends对象。
Block编译中间态与运行时状态对比
利用lldb打印出来的结果
局部*变量
//局部变量
__block NSMutableArray *friends = [NSMutableArray array];;
void(^completeBlock)(NSString *) = ^(NSString *name) {
NSLog(@"%@--%@",name,friends);
}; (lldb) expression -P -- completeBlock
(void (^)(NSString *)) $ = 0x000000010a061130 {
__isa = __NSMallocBlock__
__flags = -
__reserved =
__FuncPtr = 0x000000010a061130 (iOS_KnowledgeStructure`__main_block_invoke at main.m:) {}
}
利用clang转换后的C\C++源码
struct __main_block_impl_0 {
struct __block_impl impl;
struct __main_block_desc_0* Desc;
__Block_byref_friends_0 *friends; // by ref
__main_block_impl_0(void *fp, struct __main_block_desc_0 *desc, __Block_byref_friends_0 *_friends, int flags=) : friends(_friends->__forwarding) {
impl.isa = &_NSConcreteStackBlock;
impl.Flags = flags;
impl.FuncPtr = fp;
Desc = desc;
}
};
证明clang编译器和llvm编译器编译后的结果有出入。发现isa指针不一致。
编译后的为：impl.isa = &_NSConcreteStackBlock;
运行时的为：__isa = __NSMallocBlock__
原因是block类型转换情况4:“将block赋给带有__strong修饰符的id类型或者Block类型时。”
注意：
_NSConcreteMallocBlock一般不会在源码中出现，它通常在block copy到堆时出现，变化的源码：
static void *_Block_copy_internal(const void *arg, const int flags) {
struct Block_layout *aBlock;
const bool wantsOne = (WANTS_ONE & flags) == WANTS_ONE;
//
if (!arg) return NULL;
//
aBlock = (struct Block_layout *)arg;
//
if (aBlock->flags & BLOCK_NEEDS_FREE) {
// latches on high
latching_incr_int(&aBlock->flags);
return aBlock;
}
//
else if (aBlock->flags & BLOCK_IS_GLOBAL) {
return aBlock;
}
//
struct Block_layout *result = malloc(aBlock->descriptor->size);
if (!result) return (void *);
//
memmove(result, aBlock, aBlock->descriptor->size); // bitcopy first
//
result->flags &= ~(BLOCK_REFCOUNT_MASK); // XXX not needed
result->flags |= BLOCK_NEEDS_FREE | ;
//
result->isa = _NSConcreteMallocBlock;
//
if (result->flags & BLOCK_HAS_COPY_DISPOSE) {
(*aBlock->descriptor->copy)(result, aBlock); // do fixup
}
return result;
}