技术标签: v8引擎源码分析
VirtualMemory是通过mmap申请一块内存,然后进行管理。
class VirtualMemory {
public:
// Reserves virtual memory with size. address_hint代表用户想映射的地址
VirtualMemory(size_t size, void* address_hint = 0);
~VirtualMemory();
// Returns whether the memory has been reserved.
bool IsReserved();
// Returns the start address of the reserved memory.
void* address() {
ASSERT(IsReserved());
return address_;
};
// Returns the size of the reserved memory.
size_t size() {
return size_; }
// Commits real memory. Returns whether the operation succeeded.
bool Commit(void* address, size_t size);
// Uncommit real memory. Returns whether the operation succeeded.
bool Uncommit(void* address, size_t size);
private:
// 管理的内存首地址,由mmap返回,用户可以自定义
void* address_; // Start address of the virtual memory.
// 管理的内存大小
size_t size_; // Size of the virtual memory.
};
// Constants used for mmap.
static const int kMmapFd = -1;
static const int kMmapFdOffset = 0;
VirtualMemory::VirtualMemory(size_t size, void* address_hint) {
// 映射一块内存,不能访问,私有的,不映射到文件,写的时候如果没有物理内存则报错
address_ = mmap(address_hint, size, PROT_NONE,
MAP_PRIVATE | MAP_ANONYMOUS | MAP_NORESERVE,
kMmapFd, kMmapFdOffset);
size_ = size;
}
VirtualMemory::~VirtualMemory() {
// 已经分配了虚拟内存则释放
if (IsReserved()) {
if (0 == munmap(address(), size())) address_ = MAP_FAILED;
}
}
// 是否分配了虚拟内存
bool VirtualMemory::IsReserved() {
return address_ != MAP_FAILED;
}
//
bool VirtualMemory::Commit(void* address, size_t size) {
// 修改一块虚拟内存的属性,MAP_FIXED说明分配的地址一定是address,而不能由操作系统自己选择,这里是修改属性,所以地址要固定。因为这块内存已经申请过了
if (MAP_FAILED == mmap(address, size, PROT_READ | PROT_WRITE | PROT_EXEC,
MAP_PRIVATE | MAP_ANONYMOUS | MAP_FIXED,
kMmapFd, kMmapFdOffset)) {
return false;
}
UpdateAllocatedSpaceLimits(address, size);
return true;
}
// 修改某块虚拟内存的属性,变成不可访问
bool VirtualMemory::Uncommit(void* address, size_t size) {
return mmap(address, size, PROT_NONE,
MAP_PRIVATE | MAP_ANONYMOUS | MAP_NORESERVE,
kMmapFd, kMmapFdOffset) != MAP_FAILED;
}
PlatformData 是管理线程中,不同系统中的数据。这里只看linux系统。只保存了线程id。
class ThreadHandle::PlatformData : public Malloced {
public:
explicit PlatformData(ThreadHandle::Kind kind) {
Initialize(kind);
}
void Initialize(ThreadHandle::Kind kind) {
switch (kind) {
case ThreadHandle::SELF: thread_ = pthread_self(); break;
case ThreadHandle::INVALID: thread_ = kNoThread; break;
}
}
pthread_t thread_; // Thread handle for pthread.
};
ThreadHandle是对PlatformData的封装。
ThreadHandle::ThreadHandle(Kind kind) {
data_ = new PlatformData(kind);
}
void ThreadHandle::Initialize(ThreadHandle::Kind kind) {
data_->Initialize(kind);
}
ThreadHandle::~ThreadHandle() {
delete data_;
}
bool ThreadHandle::IsSelf() const {
// 当前执行的线程是不是管理的线程
return pthread_equal(data_->thread_, pthread_self());
}
bool ThreadHandle::IsValid() const {
return data_->thread_ != kNoThread;
}
3 Thread
// Thread
//
// Thread objects are used for creating and running threads. When the start()
// method is called the new thread starts running the run() method in the new
// thread. The Thread object should not be deallocated before the thread has
// terminated.
class Thread: public ThreadHandle {
public:
// Opaque data type for thread-local storage keys.
enum LocalStorageKey {
};
// Create new thread.
Thread();
virtual ~Thread();
// Start new thread by calling the Run() method in the new thread.
void Start();
// Wait until thread terminates.
void Join();
// Abstract method for run handler.
virtual void Run() = 0;
// Thread-local storage.
static LocalStorageKey CreateThreadLocalKey();
static void DeleteThreadLocalKey(LocalStorageKey key);
static void* GetThreadLocal(LocalStorageKey key);
static void SetThreadLocal(LocalStorageKey key, void* value);
// A hint to the scheduler to let another thread run.
static void YieldCPU();
private:
class PlatformData;
PlatformData* data_;
DISALLOW_EVIL_CONSTRUCTORS(Thread);
};
Thread::Thread() : ThreadHandle(ThreadHandle::INVALID) {
}
Thread::~Thread() {
}
// arg是this指针,见Start函数
static void* ThreadEntry(void* arg) {
Thread* thread = reinterpret_cast<Thread*>(arg);
// This is also initialized by the first argument to pthread_create() but we
// don't know which thread will run first (the original thread or the new
// one) so we initialize it here too.
/*
这里也设置一下线程id,因为如果新建完线程后,是新建的线程先执行,
这时候pthread_create还没有给thread_赋值,然后在执行Run的时候如果使用thread_就有问题,还是空的
*/
thread->thread_handle_data()->thread_ = pthread_self();
ASSERT(thread->IsValid());
// 子类需要实现的函数
thread->Run();
return NULL;
}
void Thread::Start() {
// 创建一个线程,执行ThreadEntry函数,把线程id保存在thread_
pthread_create(&thread_handle_data()->thread_, NULL, ThreadEntry, this);
ASSERT(IsValid());
}
// 挂起,等待线程thread_结束
void Thread::Join() {
pthread_join(thread_handle_data()->thread_, NULL);
}
// 创建一个用于线程保存数据kv结构体。保存返回的key,通过key可以访问value
Thread::LocalStorageKey Thread::CreateThreadLocalKey() {
pthread_key_t key;
int result = pthread_key_create(&key, NULL);
USE(result);
ASSERT(result == 0);
return static_cast<LocalStorageKey>(key);
}
// 删除线程的数据
void Thread::DeleteThreadLocalKey(LocalStorageKey key) {
pthread_key_t pthread_key = static_cast<pthread_key_t>(key);
int result = pthread_key_delete(pthread_key);
USE(result);
ASSERT(result == 0);
}
// 通过key获取数据
void* Thread::GetThreadLocal(LocalStorageKey key) {
pthread_key_t pthread_key = static_cast<pthread_key_t>(key);
return pthread_getspecific(pthread_key);
}
// 通过key写入数据
void Thread::SetThreadLocal(LocalStorageKey key, void* value) {
pthread_key_t pthread_key = static_cast<pthread_key_t>(key);
pthread_setspecific(pthread_key, value);
}
// 让优先级比自己高或者等于自己的线程执行,如果没有,则自己继续执行
void Thread::YieldCPU() {
sched_yield();
}
Mutex是基类,具体实现在子类。
class Mutex {
public:
virtual ~Mutex() {
}
// Locks the given mutex. If the mutex is currently unlocked, it becomes
// locked and owned by the calling thread, and immediately. If the mutex
// is already locked by another thread, suspends the calling thread until
// the mutex is unlocked.
virtual int Lock() = 0;
// Unlocks the given mutex. The mutex is assumed to be locked and owned by
// the calling thread on entrance.
virtual int Unlock() = 0;
};
LinuxMutex 是对linux下线程的封装。
class LinuxMutex : public Mutex {
public:
LinuxMutex() {
pthread_mutexattr_t attrs;
// 初始化属性结构体,用于设置互斥的一些属性,或者说策略
int result = pthread_mutexattr_init(&attrs);
ASSERT(result == 0);
// 设置加锁类型,支持一个线程多次(递归)获得一个锁
result = pthread_mutexattr_settype(&attrs, PTHREAD_MUTEX_RECURSIVE);
ASSERT(result == 0);
// 初始化互斥变量
result = pthread_mutex_init(&mutex_, &attrs);
ASSERT(result == 0);
}
virtual ~LinuxMutex() {
pthread_mutex_destroy(&mutex_); }
// 对linx线程的封装
virtual int Lock() {
int result = pthread_mutex_lock(&mutex_);
return result;
}
virtual int Unlock() {
int result = pthread_mutex_unlock(&mutex_);
return result;
}
private:
pthread_mutex_t mutex_; // Pthread mutex for POSIX platforms.
};
// Semaphore
//
// A semaphore object is a synchronization object that maintains a count. The
// count is decremented each time a thread completes a wait for the semaphore
// object and incremented each time a thread signals the semaphore. When the
// count reaches zero, threads waiting for the semaphore blocks until the
// count becomes non-zero.
class Semaphore {
public:
virtual ~Semaphore() {
}
// Suspends the calling thread until the counter is non zero
// and then decrements the semaphore counter.
virtual void Wait() = 0;
// Increments the semaphore counter.
virtual void Signal() = 0;
};
class LinuxSemaphore : public Semaphore {
public:
// 初始化信号量,资源数是count个
explicit LinuxSemaphore(int count) {
sem_init(&sem_, 0, count); }
virtual ~LinuxSemaphore() {
sem_destroy(&sem_); }
// 没有可用资源,需要等待
virtual void Wait() {
sem_wait(&sem_); }
// 多一个可用资源,如果有线程等待,则会被唤醒
virtual void Signal() {
sem_post(&sem_); }
private:
// linux信号量结构体
sem_t sem_;
};
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