4.2.3 Freeing Persistent Memory

Just like any actor, a restartable actor can free persistent memory blocks using pmmFree() or pmmFreeAll(). This is described in "3.4.2 Freeing a Persistent Memory Block Explicitly".

Restartable actors which allocate memory with pmmAllocate() can also use a simple, automatic de-allocation mechanism provided by the Hot Restart Controller. This saves the actor from having to free its persistent memory explicitly. Instead, the persistent memory will remain allocated for the lifetime of the actor's group, and then be freed automatically by the Hot Restart Controller when the last member of the actor's restart group terminates cleanly. The disadvantage of this system is that the lifetime of the restart group may extend well beyond the point at which the memory block is no longer needed. In this case the memory block will take up space in persistent memory unnecessarily.

To mark a persistent memory block for automatic de-allocation by the Hot Restart Controller, pass the macros HR_GROUP_KEY and HR_GROUP_KEYSIZE as the delKey and delKeySize arguments respectively in the call to pmmAllocate(). These macros tie the lifetime of the persistent memory block to the lifetime of the calling actor's restart group.

A block marked for automatic de-allocation by the Hot Restart Controller can still be freed explicitly by calling pmmFree() with the block's PmmName. However, attempting to call pmmFreeAll() by passing the HR_GROUP_KEY and HR_GROUP_KEYSIZE macros will result in an error, as this is not permitted.