core: segment/segmenter + segment/budget (stage 6)

sami/vdm

vdm/ids.hpp — TaskId, an opaque engine handle (DAEMON keeps the wire
UUID <-> TaskId map; the engine never sees the UUID).

segment/segmenter — per-download range management (docs/04 §3). Initial
lazy split; assign_slot() splits the largest remaining range when the
budget grants a slot; on_complete(may_steal) either *steals* the second
half of the largest remaining range for the same worker (slot-neutral) or
returns nullopt so the caller *yields* the slot (ADR 0011 A1); on_failed()
returns requeue only on the 3rd consecutive connection error with a mirror
present — the remaining range is orphaned and re-split. Non-resumable or
unknown-size => exactly 1 segment; never split below min_segment_bytes
(1 MiB). Resume ctor rebuilds from a persisted table (falls back to a
fresh layout if it doesn't tile [0,total)). One mutex == "the task lock";
segment fields are std::atomic and the store is a std::deque so a steal's
append never moves a worker's record.

segment/budget — the global allocator (ADR 0011). Owns exactly one
ceiling (maxActiveSegments) and min-1-before-seconds fairness: a two-pass
allocation (guarantee pass gives every wanting task 1 slot in DAEMON's
priority order, then a growth pass round-robins the rest up to each
task's effective cap = min(per_task_cap, host cap, 1 if non-resumable)),
recomputed from scratch on every edge so a live set_max_active_segments
cut naturally yields the excess lowest-priority-first, never a
mid-segment kill. DAEMON-facing surface exactly as promised in
daemon/docs/core-requests-m1.md / ADR 0011: budget(), segments_active(),
starved_tasks(), starved_since(), set_max_active_segments (drain),
set_host_segment_cap, set_task_order, on_budget_changed (a jthread
coalesces at <=4 Hz; the tasks_starved 0<->nonzero edge fires
immediately). Callbacks are copied out and run after the lock is
dropped.

Tests: segmenter split/steal/requeue/resume math + a concurrent
steal-and-advance run; budget min-1 under a tight budget, round-robin
growth, host-cap and non-resumable clamps, live-lower shedding
lowest-priority-first, starvation below the task count, starved-edge
notification, and a concurrent set_want hammer. Green under ASan/UBSan;
the steal path and the budget green under TSan.

Co-Authored-By: Claude Sonnet 5 <[email protected]>
Claude-Session: https://claude.ai/code/session_01HPPSGhiArbvQgwC2DNiURS

This commit is contained in:

sami

2026-09-10 15:14:14 +04:00

co-authored by

Claude Sonnet 5

parent 1fabaf805d

commit 5d81b4cdae

9 changed files with 1485 additions and 0 deletions

									
										core/CMakeLists.txt
									
		+2
		
												View File
												
				@@ -20,6 +20,8 @@ add_library(veloxcore STATIC

				    src/io/sparse_file.cpp

				    src/io/write_buffer.cpp

				    src/meta/veloxpart.cpp

				    src/segment/segmenter.cpp

				    src/segment/budget.cpp

				)

				add_library(velox::core ALIAS veloxcore)