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#ifndef _JFLIB_POOL_H_
#define _JFLIB_POOL_H_
#include <jellyfish/circular_buffer.hpp>
#include <jellyfish/locks_pthread.hpp>
#include <vector>
#include <stdexcept>
namespace jflib {
/** Fixed size pool of objects with lock-free access. Conceptually,
* there are two sides: A and B. There are 2 FIFOs in opposite
* direction between A and B. One "get" an element from one side
* (say A) and then "release" it. This correspond to dequeue from
* the queue B->A then enqueueing into A->B. To get an element can
* block if the queue is empty but to release never does.
*
* The class itself manages 'size' elements in the queues and are
* initialized with 'value'. Initially, all the elements are in the
* B->A queue.
*
* The elements of type T in the pool should not be accessed
* unless one has the obtained the elt object and has not released
* (or destructed) it.
*
* WARNING: The iterator on the elements does not check any of this
* and is not thread-safe.
*/
template<typename T, typename CV = jellyfish::locks::pthread::cond>
class pool {
class side;
public:
// typedef typename std::vector<T> Tvec;
typedef T* iterator;
pool(size_t size) :
size_(size), elts_(new T[size]), B2A(size, elts_), A2B(size, elts_)
{
B2A.other_ = &A2B;
A2B.other_ = &B2A;
for(uint32_t i = 0; i < size_; ++i)
B2A.fifo_.enqueue(i);
}
virtual ~pool() {
delete [] elts_;
}
size_t size() const { return size_; }
/** Get the side A. Used to get an element from side A. */
side &get_A() { return B2A; }
/** Get the side B. Used to get an element from side B. */
side &get_B() { return A2B; }
void close_A_to_B() { A2B.fifo_.close(); A2B.signal(true); }
void close_B_to_A() { B2A.fifo_.close(); B2A.signal(true); }
bool is_closed_A_to_B() const { return A2B.fifo_.is_closed(); }
bool is_closed_B_to_A() const { return B2A.fifo_.is_closed(); }
/** Iterators on the elements. Unlike other
*/
T* begin() { return elts_; }
T* end() { return elts_ + size_; }
/** A wrapper around an element of type T. The element can be
* obtained with operator* or operator->. release() is called by
* the destructor to requeue the element in to the double
* fifo. When the double fifo is empty and closed, the element
* obtained is_empty() method returns true.
*/
class elt {
public:
elt() : i_(cbT::guard), v_(0), s_(0) { }
elt(side &s) : i_(s.get()), v_(s[i_]), s_(s.other_) { }
~elt() { release(); }
elt &operator=(side &s) {
release();
i_ = s.get();
v_ = s[i_];
s_ = s.other_;
return *this;
}
void release() {
if(v_)
s_->release(i_);
v_ = 0;
}
bool is_empty() const { return v_ == 0; }
T &operator*() { return *v_; }
T *operator->() { return v_; }
friend class pool;
private:
elt(const elt &rhs) { }
elt &operator=(const elt &rhs) { }
uint32_t i_; // Index of stored value
T *v_; // Stored value
side *s_; // Side to release to
};
static const elt closed;
private:
typedef circular_buffer<uint32_t> cbT;
/** A circular buffer with a conditional variable to wait in the
* empty event and a pointer to the other direction circular
* buffer. Every method is private and are accessible only by its
* friends :)
*/
class side {
private:
friend class pool;
friend class elt;
enum State { NONE, WAITING, CLOSED };
side(size_t size, T* elts) :
fifo_(2*size), state_(NONE), other_(0), elts_(elts) { }
uint32_t get();
T *operator[](uint32_t i);
void release(uint32_t i);
void signal(bool force = false);
cbT fifo_;
CV cond_;
State state_;
side *other_;
T *elts_;
};
size_t size_;
T* elts_;
side B2A; // Manages queue from B->A
side A2B; // Manages queue from A->B
};
}
template<typename T, typename CV>
uint32_t jflib::pool<T, CV>::side::get() {
bool last_attempt = false;
uint32_t res = fifo_.dequeue();
while(res == cbT::guard) {
cond_.lock();
switch(a_load(state_)) {
case CLOSED:
if(last_attempt) {
cond_.unlock();
return cbT::guard;
} else {
last_attempt = true;
break;
}
case NONE:
a_store(state_, WAITING);
break;
case WAITING:
break;
}
res = fifo_.dequeue();
if(res == cbT::guard) {
if(last_attempt) {
cond_.unlock();
break;
}
} else {
cond_.unlock();
break;
}
do {
cond_.timedwait(5);
} while(a_load(state_) == WAITING);
cond_.unlock();
}
return res;
}
template<typename T, typename CV>
T * jflib::pool<T, CV>::side::operator[](uint32_t i) {
if(i == cbT::guard)
return 0;
return &elts_[i];
}
template<typename T, typename CV>
void jflib::pool<T, CV>::side::release(uint32_t i) {
while(!fifo_.enqueue(i)) ;
signal();
}
template<typename T, typename CV>
void jflib::pool<T, CV>::side::signal(bool close) {
if(a_load(state_) != NONE || close) {
cond_.lock();
a_store(state_, close ? CLOSED : NONE);
cond_.broadcast();
cond_.unlock();
}
}
#endif /* _JFLIB_POOL_H_ */
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