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Allegro CL 9.0 InternalsDuane Rettig

ILC 2012

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Overview

• SMP Design Internals

• Fasl reader rewrite in Lisp

• Debugger Enhancements

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SMP design goals

• Low Overhead for scalar operation

• Source Compatible

• Warnings for unsafe usage

• Tools for smp enhanced programming

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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)

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SMP: Goal Realization

• Source Compatible: Success

• Exceptions:

• hash-tables

• threads

• 4 new smp runtime-lisp files (compare 28 for new port)

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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)

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SMP: goal realization

• Tools for enhanced SMP programming

• synchronizing operators and locks

• Separate GC

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SMP: implementation

• Deprecation of SMP-unsafe Macros

• New macros

• Bindability and settability of specials

• synchronization operators

• GC

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SMP: implementation

S

• Deprecated smp-unsafe macros

• without-interrupts, without-scheduling

• excl::fast / excl::atomically

• excl::*warn-smp-usage*

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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

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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

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SMP:implementationold 8.1wide binding

headersize

valuewaste

symbol

headersize

global valuethread 1 locativethread 2 locative

thread 3 locativethread 4 locative

symbol locatives

headersize

valuewaste

sv-vectortag=type=

#xb

tag=2/type=#x70

tag=2/type=#x70

headervaluehash

functionnameplist

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SMP:implementationnew wide binding

headervaluehash

functionnameplistsv-

vectorlock-

index

headervalue

symbolfunction

symbol

headersize

symbolthread 1 locativethread 2 locative

thread 3 locativethread 4 locative

symbol locatives

headervalue

symbolfunction

sv-vectortag=type=

#xbtag=#xb/

type=#x8btag=2/

type=#x85

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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)

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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!)

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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

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SMP: implementation

• Lowest level operators

• gc-setf-protect-atomic

• ll :cas low-level instruction form

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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

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SMP: implementation

• Other higher-level synchronizing tools

• sharable-locks

• barriers

• queues (uses process-lock; with-locked-object is lighter weight)

• condition-variables

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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

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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

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GC state diagram

Lisping(0)

Foreign(1)

Blocking GC(2)

Beside GC(4)

Blocked by GC

(3)

thread goes lisping

thread goes foreign

GCDone

GCStarting

GC Starting (signal

thread:GC waits)

thread goes foreign

threadgoes

lisping

(threadwaits)

GC Done(post thread)

threadinvokes GC

threadinvokes GC

(thread waits)

(thread waits)

(post gc)22

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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

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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:

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DEBugger enhancements

• frame descriptor caching and validation

• source level debugger

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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

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Frame descriptors

• Frame-descriptors are now larger

• newer, older, chain slots

• validated via interlock with their real frames.

• frame descriptor has argcount shadow slot

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frames

(link)

return adddress

function

argcount

...

headerclass

fpnewerolderchain

(argcount)others ...

Stack Frame descrptor

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Frame descriptors

• db:next-newer-frame is no longer programming suicide!

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source level debugger

• Demo