[英]Scoped mutex lock
I never really worked with mutexes before, but i need to control access to protected resources. 我以前从未真正使用过互斥锁,但是我需要控制对受保护资源的访问。 Looking through the new C++11 stuff, i cooked up this class:
查看新的C ++ 11内容,我完成了此类:
class CMutex
{
public:
class Lockable
{
friend class CMutex;
std::atomic_flag flag;
public:
Lockable()
{
flag.clear();
}
};
private:
Lockable * resource;
CMutex(const CMutex &);
public:
CMutex(Lockable * l)
{
resource = l;
acquire(l);
}
CMutex(Lockable & l)
{
resource = &l;
acquire(l);
}
CMutex()
: resource(nullptr)
{
}
~CMutex()
{
if (resource)
release(resource);
}
void acquire(Lockable * l)
{
if (!resource)
resource = l;
if (!spinLock(2000, resource))
//explode here
return;
}
void acquire(Lockable & l)
{
acquire(&l);
}
private:
void release(Lockable * l)
{
if (l)
l->flag.clear();
}
static bool spinLock(int ms, Lockable * bVal)
{
using namespace Misc;
long start;
int ret;
loop:
start = QuickTime();
while (bVal->flag.test_and_set()) {
if ((QuickTime() - start) > ms)
goto time_out;
// yield thread
Delay(0);
}
// normal exitpoint
return true;
// deadlock occurs
time_out:
// handle error ...
}
}
Usage like so: 用法如下:
class MyClass : public CMutex::lockable
{
...
void doStuff()
{
// lock data
CMutex(this);
// do stuff
...
// mutex should automagically be RAII released here
}
...
};
First of all, I'm interested in whether this concept actually works how it should (given the implementation of std::atomic etc.)? 首先,我对这个概念是否真正起作用感到兴趣(考虑到std :: atomic等的实现)?
Secondly, I noticed that it correctly obtains the lock, however it releases it instantly. 其次,我注意到它可以正确获取锁,但是会立即释放它。 I guess i should give the lock a name?
我想我应该给锁起个名字吗?
CMutex lock(this);
However, isn't the compiler free to destruct the object before the scope is left as an optimization provided it can guarantee that i wont interact more with the object? 但是,在保留范围作为优化之前,编译器是否可以自由地销毁对象,前提是它可以保证我不会与该对象进行更多的交互? This would defeat the purpose of this construct, if i can't guarantee that the destructor only will be called at scope exit.
如果我不能保证仅在范围出口处调用析构函数,这将破坏此构造的目的。
Regards 问候
No, the compiler is not free to destruct before the scope ends. 不,在范围结束之前,编译器不能随意销毁。
Per the C++ Standard section 12.4/10 — for constructed objects with automatic storage duration (3.7.3) when the block in which an object is created exit. 根据C ++标准第12.4 / 10节-当在其中创建对象的块退出时,具有自动存储持续时间(3.7.3)的构造对象。
Here is a trick that may come handy for you and it works with all mainstream (VC++, clang, gcc) compilers: 这是一个技巧,可能适合您,并且适用于所有主流(VC ++,clang和gcc)编译器:
#define APPEND_ID1(id1, id2) id1##id2
#define APPEND_ID2(id1, id2) APPEND_ID1(id1, id2)
#define APPEND_COUNTER(id) APPEND_ID2(id, __COUNTER__)
#define SCOPED_LOCK(lockable) CMutex APPEND_COUNTER(scoped_lock)(lockable)
class MyClass : public CMutex::lockable
{
...
void doStuff()
{
// lock data
SCOPED_LOCK(this);
// auto-generates a unique name, works even with multiple locks in the same scope..
SCOPED_LOCK(that);
// do stuff
...
// mutex should automagically be RAII released here
}
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