Created
December 4, 2020 15:50
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First draft at a lock-free vector
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namespace fbw { | |
template<typename T> | |
class atomic_vector { | |
public: | |
atomic_vector(N) { | |
buffer* b = aligned_alloc( | |
alignof(buffer), | |
sizeof(buffer) + | |
N * sizeof(atomic<T>) | |
); | |
b->buffer(); | |
for(int i=0;i<N;i++){ | |
b->array[i].store(T(), | |
mo_relaxed); | |
} | |
apbuff.store(b, | |
mo_relaxed); | |
size.store(0,mo_relaxed); | |
} | |
~atomic_vector_base() { | |
buffer* b = apbuff.load( | |
mo_relaxed); | |
int N = b->capacity; | |
for(int i=0; i<N; i++) { | |
b->array[i].~T(); | |
}; | |
aligned_free(b); | |
} | |
emplace_back(T val) { | |
int idx = | |
size.fetch_add(1); | |
T temp; | |
while(!CASimpl(temp,val)); | |
} | |
pop_back() { | |
size.fetch_sub(1); | |
} | |
shrink_to_fit() { | |
shrink_impl(); | |
} | |
clear() { | |
size.store(0); | |
shrink_impl(); | |
} | |
reference | |
operator[](size_t idx) { | |
return reference(idx,this); | |
} | |
class reference { | |
size_t idx | |
atomic_vector* v; | |
operator T() { | |
return load(); | |
} | |
T load() { | |
T temp = T(); | |
T other = T(); | |
v->CASimpl(idx,temp,other) | |
return temp; | |
} | |
T exchange(T val) { | |
T temp; | |
while(! | |
v->CASimpl(idx,temp,val)); | |
} | |
void store(T val) { | |
return (void)exchange(val); | |
} | |
bool compare_exchange( | |
T& expected, | |
T& desired){ | |
return v->CASimpl( | |
idx,expected, | |
desired); | |
} | |
}; // class reference | |
friend class reference; | |
private: | |
atomic<buffer*> apbuff; | |
atomic<long> size; | |
void reserveimpl(size_t idx){ | |
buffer* b = | |
aligned_alloc( | |
alignof(buffer), | |
sizeof(buffer)+ | |
idx*sizeof(T); | |
b->capacity = idx; | |
dptr d; | |
do { | |
d = {getptr(),nullptr}; | |
} while(ptr.cas(d,{b,d.new}; | |
hptr<0>().store(nullptr); | |
} | |
buffer* getsizebuffer( | |
size_t idx) { | |
buffer* b = getptr(); | |
if(idx > b->capacity) { | |
reserve( | |
max(idx,b->size*2)); | |
continue; | |
} | |
size_t sizel; | |
while(!size.casw(sizel, | |
max(sizel,idx); | |
return b; | |
} | |
bool CASimpl(size_t idx, | |
T& expected, | |
T desired) { | |
T temp = expected; | |
do { | |
buffer* b = getbuffer(idx); | |
} while( | |
b->array[idx].cas(old,new) | |
&& b==getptr() | |
&& temp == expected | |
); | |
hp_thread<0>() | |
.store(nullptr); | |
delete_pending_hazards(); | |
} | |
shrink_impl() { | |
buffer* b = getptr(); | |
buffer* temp; | |
do { | |
temp=b; | |
size_t s = b->size.load(); | |
reserveimpl(s); | |
temp=b; | |
b = getptr(); | |
while(b==temp); | |
} | |
struct buffer { | |
size_t capacity; | |
atomic<T> array[0]; | |
}; | |
struct dptr { | |
buffer* new; | |
buffer* old; | |
}; | |
copy(buffer* oldbuff, | |
buffer* newbuff) { | |
size_t temp newbuff-> | |
size.load(); | |
oldbuff.store(temp); | |
for(int i=0; i<ms; i++) { | |
T temp = | |
oldbuff->array[i].load() | |
newbuff->array[i].store( | |
temp); | |
} | |
} | |
buffer* getptr() { | |
dptr d = | |
set_hazard(ptr); | |
while(d.old) { | |
copy(d.old, d.new); | |
if(ptr.cas(d, | |
{d.new,nullptr}){ | |
delete_hazards(d.old); | |
} | |
d = set_hazard(ptr); | |
} | |
return d.new; | |
} | |
set_hazard( | |
atomic<dptr>& atom) { | |
dptr v = atom.load(); | |
do { | |
dptr temp = v; | |
hptr<0>().store(temp.new); | |
hptr<1>().store(temp.old); | |
} while (v!=temp); | |
return v; | |
} | |
}; // class atomic_vector | |
} // namespace fbw |
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