class UniqueIdAllocator

Manage a set of ID values from min to max inclusive. The ID numbers that are freed will be allocated (reused) in the same order. I.e. the oldest ID numbers will be allocated.

This implementation will use 4 bytes per id number, plus a few bytes of management data. e.g. 10,000 ID numbers will use 40KB.

Also be advised that ID -1 and -2 are used internally by the allocator. If allocate returns IndexEnd (-1) then the allocator is out of free ID numbers.

There are other implementations that can better leverage runs of used or unused IDs or use bit arrays for the IDs. But, it takes extra work to track the age of freed IDs, which is required for what we wanted. If you would like to kick around other implementation ideas, please contact Schuyler.

Inheritance diagram

Inheritance diagram of UniqueIdAllocator

explicit UniqueIdAllocator(uint32_t min = 0, uint32_t max = 20)
UniqueIdAllocator(UniqueIdAllocator const&) = default

Create a free id pool in the range [min:max].

uint32_t allocate(void)

Returns an id between _min and _max (that were passed to the constructor). IndexEnd is returned if no ids are available.

PN_stdfloat fraction_used(void) const

return the decimal fraction of the pool that is used. The range is 0 to 1.0 (e.g. 75% would be 0.75).

void free(uint32_t index)

Free an allocated index (index must be between _min and _max that were passed to the constructor).

void initial_reserve_id(uint32_t id)

This may be called to mark a particular id as having already been allocated (for instance, by a prior pass). The specified id is removed from the available pool.

Because of the limitations of this algorithm, this is most efficient when it is called before the first call to allocate(), and when all the calls to initial_reserve_id() are made in descending order by id. However, this is a performance warning only; if performance is not an issue, any id may be reserved at any time.

void output(std::ostream &out) const

…intended for debugging only.

void write(std::ostream &out) const

…intended for debugging only.