Module shadow_shmem::allocator

In this module is a shared memory allocator that can be used in Shadow to share data between the main simulator process and managed processes. There are three main global functions that are provided:

(1) shmalloc(), which places the input argument into shared memory and returns a Block smart pointer. (2) shfree(), which is used to deallocate allocated blocks. (3) shdeserialize(), which is used to take a serialized block and convert it back into a Block smart pointer that can be dereferenced.

Blocks can be serialized with the .serialize() member function, which converts the block to a process-memory-layout agnostic representation of the block. The serialized block can be one-to-one converted to and from a string for passing in between different processes.

The intended workflow is:

(a) The main Shadow simulator process allocates a shared memory block containing an object. (b) The block is serialized. (c) The serialized block is turned into a string. (d) The string is passed to one of Shadow’s child, managed processes. (e) The managed process converts the string back to a serialized block. (f) The serialized block is deserialized into a shared memory block alias. (g) The alias is dereferenced and the shared object is retrieved.

Structs

• ShMemBlock
  A smart pointer class that holds a Sync and VirtualAddressSpaceIndependent object.
• ShMemBlockAlias
  This struct is analogous to the ShMemBlock smart pointer, except it does not assume ownership of the underlying memory and thus does not free the memory when dropped.
• ShMemBlockSerialized
• SharedMemAllocator
  Safe wrapper around our low-level, unsafe, nostd shared memory allocator.
• SharedMemAllocatorDropGuard
  The intended singleton destructor for the global singleton shared memory allocator.
• SharedMemDeserializer

Functions

• shdeserialize^⚠
  This function takes a serialized block and converts it back into a BlockAlias that can be dereferenced.
• shfree
  This function frees a previously allocated block.
• shmalloc
  This function moves the input parameter into a newly-allocated shared memory block. Analogous to malloc().