A scanner reading a mostly ASCII text front to back (slices and
positioned startsWith at increasing positions) walked from the hot
cursor on every read within 64 units of it, since the near-cursor walk
came before the ASCII-run growth. A forward read past the run now grows
the run first. When a non-ASCII character ends the run, a nearby read
walks from the run's end or the cursor and starts a new run where it
lands.
A new plan was copied into its slot as a whole struct, which wrote the
slot's pc with a plain store while other threads' lookups read it
atomically: a data race. The insert now copies the fields after pc and
publishes pc only with the release store.
The unwinder test also runs its threaded cases under ThreadSanitizer,
which reports the race without this change.
scr_unwind_raise walks the stack with plans cached per return address.
The first raise through a return address finds the function's FDE
through the .eh_frame_hdr of the object that contains it, runs the CFI
up to the call, and finds the call site's landing pad in the LSDA; the
plan records the frame's CFA rule, where its callee-saved registers are
saved, and the landing pad. Later raises look the plans up, restore the
registers, and jump to the first landing pad. Plans are inserted under
a lock and read without one.
Landing pads continue the unwind with scr_unwind_resume instead of
`resume`, so the walk goes on from their frame. A frame whose CFI,
pointer encodings or personality the plans do not express, or a return
address without an FDE, leaves the unwind to libgcc's forced unwind
from the frame the walk started at, as before. Other Linux targets keep
libgcc's unwinder; their scr_unwind_resume calls _Unwind_Resume.
bench:runtime gains layered-errors, a workload whose errors are thrown
below small functions that hold references and caught per entry in a
loop, and the corpus gains unwind-landing-pad-chains, which pins landing
pads that continue the unwind, including in frames LLVM inlines into a
caller whose handler takes the exception.
Worker runtimes reserve one region for 32 arenas of 40 class slices. When
the host refused the full region (32 arenas of 1 GiB slices, 1.28 TiB of
address space), the allocator kept 32 arenas and shrank every slice. Under
valgrind, which maps at most 56 GiB, slices dropped to 16 MiB, and every
class whose live blocks outgrew 16 MiB took the system allocator.
Callgrind profiles then counted system allocations that a native run
never makes: tsc-ts checking VS Code made 10.3 M small calloc calls under
valgrind and 0.06 M natively.
The reservation now tries arena counts from 32 down to 4 at each slice
size, from 1 GiB down, before smaller slices, and 2 and 1 arena only when
no slice size fits 4. Arenas that are not reserved stay claimed, so
threads beyond them use the system allocator, and the region bounds of
foreign frees use the arenas reserved. Hosts that map the full region keep
32 arenas of 1 GiB slices.
A runtime test limits RLIMIT_AS to 60 GiB and checks that the first thread
gets 256 MiB slices for 400,000 blocks of 56 bytes, that three more
threads get arenas and a fourth uses the system allocator, and that blocks
freed across threads keep their contents.
charCodeAt on a non-ASCII string mapped the UTF-16 index to a byte offset
through a string index entry, which the first read claimed and the
string's release purged. For a string of one character, such as each
character of a for-of loop that codePointAt(0) classifies, the entry cost
more than the read.
A non-ASCII receiver of up to 16 bytes is now decoded from its start on
each read, as scr_str_utf16_len already counts short receivers. Longer
receivers keep the index entry and its cursor.
A template literal of strings and numbers reserved 32 bytes for each
number, the longest number text, and kept that capacity for the result's
lifetime: an 8-byte name built from two numbers used a 96-byte block. The
numbers now format into a stack buffer first, so the result is allocated
once at its exact length.
A checked object (SCR_DYN_OBJ) now starts in layout mode: v.obj.layout names
its key sequence, a node of the thread's interned transition tree, and
v.obj.slots holds one 8-byte value per key, where every property used to take
a 48-byte entry. All properties of a layout-mode object are writable,
enumerable, configurable data properties. An accessor, a non-default
attribute, a delete, more than 64 keys, spent layout budgets, publication to
other threads, or any code that reads entries directly moves the object to
dictionary mode (today's entries) for good, so unported paths stay correct.
Layouts replace the dynamic tier's lazily computed hidden classes (ScrJsShape)
and keep their budgets. Inline caches key on the layout pointer and read the
slot directly; JSON.parse builds objects along layouts; stringify, key
enumeration, release, trace and the runtime read cache read slots in place.
The emitted index-signature checks read members through runtime accessors.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Runtime units outside the object core (scr_json.c, scr_js_object.c) read and
adjusted SCR_DYN_OBJ entries in place: v.obj.len, v.obj.entries[i] and the
48-byte ScrDynEntry fields. The single object model's generic objects
(stage S3) change that storage, so these units now go through own-property
accessors in scr_dyn.h:
- scr_dyn_obj_count, scr_dyn_obj_key_at, scr_dyn_obj_value_at and
scr_dyn_obj_prop_at (a ScrDynProp view: key, value, getter, setter and
attributes) walk the properties in creation order;
- scr_dyn_obj_index_of finds one by key;
- scr_dyn_obj_set_attrs_at restricts a member a builtin object just added;
- scr_dyn_own_symbol_prop and scr_dyn_copy_prop_at wrap the symbol-entry
and copy primitives.
The accessors are inline over today's entries, so behavior is unchanged.
21 units move (inspect, assert, util compare, console, http, http2, fetch,
tls, fs, os, lib, array, message, publish, region, symbol, worker events,
handle properties, builtin values, declaration adoption). A package test
keeps entry storage reads inside the core.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
A limited pass (scr_cyc_collect_set, which freeing a LifetimeRegion runs
over the objects the region owned) takes only the candidates in its set.
Its walk can still reach other candidates, and one that is referenced from
outside is blackened by scan and promoted to the next generation while it
keeps its slot in its old generation's buffer. scr_cyc_on_dead finds a
candidate's buffer by its generation, so when that object died it removed
another buffer's entry and left its own slot pointing at the freed block,
which the next pass then read.
Such a candidate is no longer promoted: it keeps the generation of the
buffer it is in until a pass takes it.
The test kept one live 48-byte block every 1,000 allocations, which on a
system with 64 KiB pages leaves a live block on every page, so no page held
only free blocks and the resident-memory check failed. It now keeps one
block per four pages of blocks, from the system's page size.
The native compiler's frontend-dispose sweep frees about 450 MB on a cold
tsc-ts build, but the size-class allocator keeps the freed blocks on their
classes' free lists, which only later blocks of the same size reuse. Code
generation allocates other sizes, so its pages stacked on top of the freed
heap and set the build's peak resident memory.
- scr_heap_trim (scr_alloc.c) returns the pages of the calling thread's
size-class slices that hold only free blocks (MADV_DONTNEED) and the
system allocator's free pages (malloc_trim). In the single-threaded
allocator the blocks of a returned page leave the free list and the
class carves past its frontier instead; the remaining free blocks are
relinked in address order. Worker runtimes return the calling thread's
arena pages as a parking thread does.
- scr_collect_cycles_phase, the full sweep after a phase's data died,
calls it; the native compiler calls that sweep when it disposes the
frontend.
- test_heap_trim.c checks that the pages go back, that the blocks still
allocated keep their contents, and that new blocks overlap none of
them, with and without worker arenas (another thread allocating and
freeing remotely throughout).
Cold tsc-ts build, 12 interleaved rounds: peak RSS 1407 -> 1247 MB
(-160 MB, -11.4%, every round); wall 87.1 -> 85.9 s (median).
String storage can hold bytes that are not well-formed UTF-8: an HTTP
header value keeps the raw bytes a client sent. Encoding such a string
read past its end.
- scr_bytes_next_cp decoded any high byte as the lead of a sequence and
read up to three bytes after it without a bound. It now takes the
storage length, decodes only complete, well-formed sequences, and
returns any other byte as U+0000..U+00FF, advancing by one. That is
each such byte's value in Node, which decodes header values as latin1.
This covers latin1, ascii, binary and utf16le encoding, hex and base64
of non-ASCII text (which narrow through latin1), Buffer#write and
TextEncoder#encodeInto.
- base64 decoding read one byte past its input when the eight-character
groups ended exactly at the end.
The runtime's bytes unit test (built with ASan) encodes ill-formed
storage at every offset within a word and random high bytes, and
compares latin1, ascii and utf16le with a scalar reference. A corpus
program sends such header bytes to a server and encodes them as Node
does.
A program's nursery trigger starts at 256 candidates and doubles, up to
4096, after each scheduled mature or full pass whose dead set held more
mature and old objects than an eighth of what the nursery passes freed
since the previous one; it halves after one that held less than a
thirty-second of that. SCR_CYCLE_THRESHOLD and
scr_cyc_set_nursery_threshold pin the trigger as before. The
scheduled-age rule keeps counting collection points in the pinned or
default trigger.
A versioned loop over a non-ASCII string passes the range of indexes it
reads: a counted loop's start and limit, or a while loop's counter and
bound. The runtime converts the string at once when that range has at
least one unit per 16 bytes of it, and otherwise counts the loop as one
indexed read, so a loop over a line of a long source text no longer
keeps a UTF-16 copy of all of it. The publish call is weighted as
unlikely, since loops re-entered over one string skip it.
A number-keyed Map or Set with keys the direct index allows now moves to it
at its second entry rather than its fifth, so a map over a few small
integer keys (a histogram over 0..3) reads through the inline direct index
instead of the out-of-line linear scan.
The native compiler now starts with the cycle collector's nursery trigger
at 1024 new candidates instead of 256. scr_cyc_set_nursery_threshold sets
the trigger that SCR_CYCLE_THRESHOLD sets, on the pattern of
scr_cyc_set_growth_cap; the environment variable still takes precedence.
The compiler sets it from a constructor in its host object, before its
modules initialize. Set from main, the trigger leaves the build's
collection work where it was: the cost depends on the collector's first
passes. Programs keep the default trigger.
A cold tsc-ts build takes 4% less wall time (12 paired runs) and its peak
RSS goes from 1.41 GB to 1.31 GB. The program's IR is unchanged.
uintptr_t is 32 bits on wasm32, where the weak-collection hashes shifted it by 33 and 56 bits. The hashes now widen keys, owners and kinds to uint64_t before mixing; 64-bit targets compute the same values as before.
JSON.parse's SyntaxError messages were shaped like V8's but differed from
Node's in several ways:
- Every positional message now ends with V8's "(line L column C)", where
\n, \r and \r\n end lines.
- Positions are UTF-16 offsets, as in Node, not byte offsets.
- An object or array cut off after '{', a property name, a value or an
array element reports the token V8 expected ("Expected property name or
'}'", "Expected ':' after property name", "Expected ',' or '}' after
property value", "Expected ',' or ']' after array element") instead of
"Unexpected end of JSON input".
- After a comma in an object the message is "Expected double-quoted
property name".
- An unterminated string reports the end of the input, and a truncated
\u escape is a "Bad Unicode escape" there.
- A leading zero followed by a digit is an "Unexpected number".
- A misspelled literal names the first differing character, or the end of
the input.
- An unexpected character is named with the source as V8 does: whole when
it is under 21 units, otherwise ten units of context on each side; the
sources "NaN", "Infinity", "undefined" and "[object Object]" name only
themselves; a quote or a number there is an "Unexpected string" or
"Unexpected number".
The new corpus program 7993-json-parse-error-messages pins 76 inputs
against Node, including non-ASCII text before the error, line breaks, and
long sources with split surrogate pairs at the context edges.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Chris Tate