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#ifndef UTIL_POOL_H
#define UTIL_POOL_H
#include <cassert>
#include <cstring>
#include <vector>
#include <stdint.h>
namespace util {
/* Very simple pool. It can only allocate memory. And all of the memory it
* allocates must be freed at the same time.
*/
class Pool {
public:
Pool();
~Pool();
void *Allocate(std::size_t size) {
void *ret = current_;
current_ += size;
if (current_ > current_end_) {
ret = More(size);
}
#ifdef DEBUG
base_check_ = ret;
#endif
return ret;
}
/** Extend (or contract) the most recent allocation.
* @param base The base pointer of the allocation. This must must have been
* returned by the MOST RECENT call to Allocate or Continue.
* @param additional Change in the size.
*
* In most cases, more memory from the same page is used, in which case
* base is unchanged and the function returns false.
* If the page runs out, a new page is created and the memory (from base)
* is copied. The function returns true.
*
* @return Whether the base had to be changed due to allocating a page.
*/
bool Continue(void *&base, std::ptrdiff_t additional) {
#ifdef DEBUG
assert(base == base_check_);
#endif
current_ += additional;
if (current_ > current_end_) {
std::size_t new_total = current_ - static_cast<uint8_t*>(base);
void *new_base = More(new_total);
std::memcpy(new_base, base, new_total - additional);
base = new_base;
#ifdef DEBUG
base_check_ = base;
#endif
return true;
}
return false;
}
void FreeAll();
private:
void *More(std::size_t size);
std::vector<void *> free_list_;
uint8_t *current_, *current_end_;
#ifdef DEBUG
// For debugging, check that Continue came from the most recent call.
void *base_check_;
#endif // DEBUG
// no copying
Pool(const Pool &);
Pool &operator=(const Pool &);
};
/**
* Pool designed to allow limited freeing.
* Keeps a linked list of free elements in the free spaces.
* Will not reduce in size until FreeAll is called.
*/
class FreePool {
public:
explicit FreePool(std::size_t element_size)
: free_list_(NULL),
element_size_(element_size),
padded_size_(std::max(element_size_, sizeof(void*))) {}
void *Allocate() {
if (free_list_) {
void *ret = free_list_;
free_list_ = *reinterpret_cast<void**>(free_list_);
return ret;
} else {
return backing_.Allocate(padded_size_);
}
}
void Free(void *ptr) {
*reinterpret_cast<void**>(ptr) = free_list_;
free_list_ = ptr;
}
std::size_t ElementSize() const { return element_size_; }
private:
void *free_list_;
Pool backing_;
const std::size_t element_size_;
const std::size_t padded_size_;
};
} // namespace util
#endif // UTIL_POOL_H
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