Function alloc

pub fn alloc<VM: VMBinding>(
    mutator: &mut Mutator<VM>,
    size: usize,
    align: usize,
    offset: usize,
    semantics: AllocationSemantics,
) -> Address

Allocate memory for an object.

When the allocation is successful, it returns the starting address of the new object. The memory range for the new object is size bytes starting from the returned address, and RETURNED_ADDRESS + offset is guaranteed to be aligned to the align parameter. The returned address of a successful allocation will never be zero.

If MMTk fails to allocate memory, it will attempt a GC to free up some memory and retry the allocation. After triggering GC, it will call crate::vm::Collection::block_for_gc to suspend the current thread that is allocating. Callers of alloc must be aware of this behavior. For example, JIT compilers that support precise stack scanning need to make the call site of alloc a GC-safe point by generating stack maps. See alloc_with_options if it is undesirable to trigger GC at this allocation site.

If MMTk has attempted at least one GC, and still cannot free up enough memory, it will call crate::vm::Collection::out_of_memory to inform the binding. The VM binding can implement that method to handle the out-of-memory event in a VM-specific way, including but not limited to throwing exceptions or errors. If crate::vm::Collection::out_of_memory returns normally without panicking or throwing exceptions, this function will return zero.

For performance reasons, a VM should implement the allocation fast-path on their side rather than just calling this function.

Arguments:

• mutator: The mutator to perform this allocation request.
• size: The number of bytes required for the object.
• align: Required alignment for the object.
• offset: Offset associated with the alignment.
• semantics: The allocation semantic required for the allocation.