Consolidated and concurrent remapping and identification for colorless roots

Abstract

During a concurrent Relocation Phase, a GC thread relocates live objects, as an application thread executes. References in a frame on a call stack are remapped if the application thread attempts to access the frame. References on the call stack remains stale if no application thread attempts access. The GC thread may proceed with a subsequent phase of a GC cycle, even if a frame has stale references and therefore has not assumed a remap state. During a concurrent Mark/Remap Phase, the call stack may include frames in different frame states. The GC thread selects appropriate operations for processing each frame based on the respective frame state. When the GC thread encounters a frame not in the remap state, references therein are first remapped, and then identified as roots. Hence, root reference remapping and identification are performed in a single concurrent phase of a GC cycle.