Organize outdated tx block into a linked list: finish linked list pointer but append/remove operation in gc threads has not yet implemented.
Enforce each log entry block is only referenced by at most one tx block.
Each tx block has a tx_seq and a gc_seq. tx_seq is designed previously; gc_seq must be zero for all app threads allocated tx block. Each time a gc operation starts, it acquires a monotonically increasing gc_seq and assigns this number to each tx block allocated by this gc operation. One may consider gc_seq as a version number so that tx_seq can be not reused.
TODO:
Each thread must publish on shared-memory for which tx block it is reading.
Implement:
TODO: