1 Allegro CL 9.0 Internals Duane Rettig ILC 2012

2 Overview SMP Design Internals Fasl reader rewrite in Lisp Debugger Enhancements

3 SMP design goals Low Overhead for scalar operation Source Compatible Warnings for unsafe usage Tools for smp enhanced programming

4 SMP: Goal Realization Low Overhead 9.0 (non-smp) virtually the same as 8.2 SMP has <10% hit over non-smp (sometimes faster) Other lisps have 15%-100% hit over 8.2 (YMMV)

5 SMP: Goal Realization Source Compatible: Success Exceptions: hash-tables threads 4 new smp runtime-lisp files (compare 28 for new port)

6 SMP: Goal realization Warnings for unsafe usage smp-macros module (8.1 patch, integral in 8.2) not aggressive in looking for problems setf races potential deadlocks alists (but plists/getf are protected by convention)

7 SMP: goal realization Tools for enhanced SMP programming synchronizing operators and locks Separate GC

8 SMP: implementation Deprecation of SMP-unsafe Macros New macros Bindability and settability of specials synchronization operators GC

9 SMP: implementation S Deprecated smp-unsafe macros without-interrupts, without-scheduling excl::fast / excl::atomically excl::*warn-smp-usage*

10 SMP: Implementation New Macros fast-and-clean: replaces (excl::fast (excl::atomically...)) with-pinned-objects: replaces (excl::fast (excl::atomically...)) with-delayed-interrupts: replaces without- {interrupts,scheduling} defvar-nonbindable

11 SMP:Implementation Bindability and Settability bindable, settable: defvar/defparameter not bindable, settable: defvar-nonbindable bindable, not settable: excl::defvar-nonsettable not bindable, not settable: defconstant

12 SMP:implementation old 8.1wide binding header size value waste symbol header size global value thread 1 locative thread 2 locative thread 3 locative thread 4 locative symbol locatives header size value waste sv-vector tag=type=#xb tag=2/type=#x70 header value hash function name plist

13 SMP:implementation new wide binding header value hash function name plist sv-vector lock- index header value symbol function symbol header size symbol thread 1 locative thread 2 locative thread 3 locative thread 4 locative symbol locatives header value symbol function sv-vectortag=type=#xb tag=#xb/type=#x8b tag=2/type=#x85

14 smp: implementation Synchronization operators push-atomic/pop-atomic incf-atomic/decf-atomic update-atomic atomic-conditional-setf (implementor for above) atomic-conditional-setq (special operator)

15 smp: implementation Lower level smp operators get-atomic-modify-expansion excl::atomic-modify-form (may change!) excl::*force-csw-opcodes* (may change!) excl::defsetf-conditional (may change!)

16 SMP: implementation excl::defsetf-conditional built-in operator conversions excl::.inv-structure-ref excl::.inv-svref excl::.inv-car, excl::.inv-cdr excl::.inv-symbol-plist excl::.inv-global-symbol-value

17 SMP: implementation Lowest level operators gc-setf-protect-atomic ll :cas low-level instruction form

18 SMP: implementation with-locked-object good on any lockable object lighter weight than process-lock use with care to avoid deadlocks special versions for structs and streams

19 SMP: implementation Other higher-level synchronizing tools sharable-locks barriers queues (uses process-lock; with-locked-object is lighter weight) condition-variables

20 SMP Implementation: gc Runs in separate (non-Lisp) thread Able to provide per-thread object allocation Currently implemented: conses: everywhere floats: on x86-64 Synchronizes with all threads Still written in C

21 GC states 0: Lisping: thread is running Lisp code; GC can’t happen 1: Foreign: thread is running foreign code; GC can happen 2: Blocking GC: thread is running Lisp code; GC wants it to pause 3: Blocked by GC: thread is trying to get from foreign to Lisp; GC is running 4: Beside GC: thread is running foreign code and GC is happening

22 GC state diagram Lisping (0) Foreign (1) Blocking GC (2) Beside GC (4) Blocked by GC (3) thread goes lisping thread goes foreign GC Done GC Starting GC Starting (signal thread:GC waits) thread goes foreign thread goes lisping (thread waits) GC Done (post thread) thread invokes GC thread invokes GC (thread waits) (post gc) 22

23 Fasl Reader Rewritten in Lisp runtime code 50% faster than C version fewer transitions to/from C Started in 8.2; used only to load source debug info Used exclusively in 9.0

24 Fasl coding example case ff_complex:/* tos = imag, tos-1 = real */if (Building_BOTH) { LispVal comp = new_lisp_obj(TYPEcomplex, 0, 0); /* complex object is new */ *(nat *)((nat)comp + c_imag_adj/PtrScale) = (nat)f_pop(); *(nat *)((nat)comp + c_real_adj/PtrScale) = (nat)f_pop(); f_push(comp); }break; (#.ff_complex (when (building-both) (let* ((imag (fasl-pop thread)) (real (fasl-pop thread)) (complex (q-qint-call sys::make-complex real imag))) (fasl-push complex thread)))) Lisp: C: 24

25 DEBugger enhancements frame descriptor caching and validation source level debugger

26 Debugger: reimplementation of Api db:next-newer-frame hard to implement Always moving! either cached frames become invalid or have to start over each time :zoom on overflowed stack takes much too long

27 Frame descriptors Frame-descriptors are now larger newer, older, chain slots validated via interlock with their real frames. frame descriptor has argcount shadow slot

28 frames (link) return adddress function argcount... header class fp newer older chain (argcount) others... Stack Frame descrptor

29 Frame descriptors db:next-newer-frame is no longer programming suicide!

30 source level debugger Demo