5. Pools

Within an arena a client program creates one or more pools. A pool is responsible for requesting memory from the arena and making it available for allocation.

mps_pool_t

The type of pools.

A pool is responsible for requesting memory from the arena and making it available to the client program via mps_alloc() or via an allocation point.

mps_res_t mps_pool_create_k(mps_pool_t *pool_o, mps_arena_t arena, mps_pool_class_t pool_class, mps_arg_s args[])

Create a pool in an arena.

pool_o points to a location that will hold a pointer to the new pool.

arena is the arena in which to create the pool.

pool_class is the pool class of the new pool.

args are keyword arguments specific to the pool class. See the documentation for the pool class.

Returns MPS_RES_OK if the pool is created successfully, or another result code otherwise.

The pool persists until it is destroyed by calling mps_pool_destroy().

void mps_pool_destroy(mps_pool_t pool)

Destroy a pool.

pool is the pool to destroy.

This function checks the consistency of the pool, destroys the pool’s internal control structures and causes the pool’s memory to be returned to the arena for reuse by other pools, or to be returned to the operating system. Blocks allocated from the pool may no longer be used.

It is an error to destroy a pool without first destroying all allocation points and segregated allocation caches created in the pool.

Warning

It is not safe to carry on running the garbage collector after destroying an automatically managed pool that contains any objects that are reachable from your roots, or any objects that have been registered for finalization but not yet finalized.

Our recommended approach is to destroy automatically managed pools just before destroying the arena, and then only while the arena is in the parked state. Thus a safe tear-down sequence looks like this:

mps_arena_park(arena);
/* destroy threads and roots belonging to the arena */
/* destroy allocation points and caches belonging to the pool */
mps_pool_destroy(pool);
/* destroy chains and formats belonging to the arena */
mps_arena_destroy(arena);

5.1. Pool classes

Pools belong to pool classes that specify policies for how their memory is managed. Some pools are manually managed (you must call mps_free() to return a block of memory to the pool) and others are automatically managed (the garbage collector reclaims unreachable blocks).

See the Pool reference for a list of pool classes.

mps_pool_class_t

The type of pool classes.

5.2. Pool introspection

size_t mps_pool_total_size(mps_pool_t pool)

Return the total memory allocated from the arena and managed by the pool.

pool is the pool.

The result includes memory in use by the client program, memory that’s available for use by the client program, and memory that’s lost to fragmentation. It does not include memory used by the pool’s internal control structures.

size_t mps_pool_free_size(mps_pool_t pool)

Return the free memory: memory managed by the pool but not in use by the client program.

pool is the pool.

The result includes memory that’s available for use by the client program, and memory that’s lost to fragmentation. It does not include memory used by the pool’s internal control structures.

mps_bool_t mps_addr_pool(mps_pool_t *pool_o, mps_arena_t arena, mps_addr_t addr)

Determine the pool to which an address belongs.

pool_o points to a location that will hold the address of the pool, if one is found.

arena is the arena whose pools will be considered.

addr is the address.

If addr is the address of a location inside a block allocated from a pool in arena, then update the location pointed to by pool_o with the address of the pool, and return true.

If addr points to a location that is not managed by arena, return false.

If neither of the above conditions is satisfied, mps_addr_pool() may return either true or false.

Note

This function might return a false positive by returning true if you ask about an address that happens to be inside memory managed by a pool, but which is not inside a block allocated by that pool. It never returns a false negative.

The result from this function is valid only at the instant at which the function returned. In some circumstances the result may immediately become invalidated. For reliable results call this function and interpret the result while the arena is in the parked state.