> On Jan 5, 2021, at 4:18 AM, Marcel Taeumel <marcel.taeumel at hpi.de> wrote:
> 
> 
> Hi Dave.
> 
> > Provide vmParameterAt:default: to handle primitive failure on reading VM parameters.
> 
> Hmm... #vmParameterAt:ifAbsent: would be "more idiomatic"?

or vmParameterAt:ifFail:

No matter which selector I like this very much.  It’s a good idea Dave.  Just upload to trunk what you like best.

> 
> Best,
> Marcel
>> Am 28.12.2020 16:50:22 schrieb commits at source.squeak.org <commits at source.squeak.org>:
>> 
>> David T. Lewis uploaded a new version of System to project The Inbox:
>> http://source.squeak.org/inbox/System-dtl.1209.mcz
>> 
>> ==================== Summary ====================
>> 
>> Name: System-dtl.1209
>> Author: dtl
>> Time: 28 December 2020, 10:50:06.875257 am
>> UUID: 25efba24-561f-4c53-97d9-95438edfce90
>> Ancestors: System-eem.1207
>> 
>> Provide vmParameterAt:default: to handle primitive failure on reading VM parameters.
>> Supply default parameter values to mock possibly missing elements in the parameters array.
>> Remove two unnecessary isRunningCog checks and an ifNotNil:
>> Remove inappropriate halt in sendMouseWheelEvents:
>> Let supportsMultipleBytecodeSets and supportsReadOnlyObjects work on any VM.
>> 
>> =============== Diff against System-eem.1207 ===============
>> 
>> Item was changed:
>> ----- Method: SmalltalkImage>>isRunningCog (in category 'system attributes') -----
>> isRunningCog
>> "Answers if we're running on a Cog VM (JIT or StackInterpreter)"
>> 
>> + ^(self vmParameterAt: 42 default: nil)
>> - ^(self vmParameterAt: 42)
>> ifNil: [false]
>> ifNotNil: [:numStackPages| numStackPages > 0]!
>> 
>> Item was changed:
>> ----- Method: SmalltalkImage>>isRunningCogit (in category 'system attributes') -----
>> isRunningCogit
>> "Answers if we're running on the Cog JIT"
>> 
>> + ^(self vmParameterAt: 46 default: nil)
>> - ^(self vmParameterAt: 46)
>> ifNil: [false]
>> ifNotNil: [:machineCodeZoneSize| machineCodeZoneSize > 0]!
>> 
>> Item was changed:
>> ----- Method: SmalltalkImage>>lowSpaceThreshold (in category 'memory space') -----
>> lowSpaceThreshold 
>> "Answer the low space threshold. When the amount of free memory (after garbage collection)
>> falls below this limit, the system is in serious danger of completely exhausting memory and
>> crashing. This limit should be made high enough to allow the user open a debugger to diagnose
>> a problem or to save the image. In a stack-based VM such as Cog contexts for activations in
>> the stack zone will have to be created as the debugger opens, requiring additional headroom."
>> 
>> | slotsForDebugger slotsForContextsOnStackPages |
>> slotsForDebugger := 65536. "Arbitrary guess"
>> slotsForContextsOnStackPages :=
>> + (self vmParameterAt: 42 default: nil)
>> - (self vmParameterAt: 42)
>> ifNil: [0]
>> ifNotNil:
>> [:numStackPages| | headerSize numActivationsPerPage maxContextSize |
>> numActivationsPerPage := 40. "Design goal of the Cog & Stack VMs"
>> headerSize := 8 / self wordSize. "64-bits for Spur"
>> maxContextSize := thisContext class instSize + CompiledMethod fullFrameSize + headerSize.
>> numStackPages * numActivationsPerPage * maxContextSize].
>> ^slotsForDebugger + slotsForContextsOnStackPages * self wordSize!
>> 
>> Item was changed:
>> ----- Method: SmalltalkImage>>maxExternalSemaphores (in category 'vm parameters') -----
>> maxExternalSemaphores
>> + "The size of table where external semaphores are registered. Only in Cog,
>> + other VMs are expected to answer nil if present in the parameters array."
>> + ^self vmParameterAt: 49 default: nil!
>> - "The size of table where external semaphores are registered. Only in Cog"
>> - self isRunningCog ifFalse: [^nil].
>> - ^self vmParameterAt: 49!
>> 
>> Item was changed:
>> ----- Method: SmalltalkImage>>maxExternalSemaphores: (in category 'vm parameters') -----
>> maxExternalSemaphores: aSize
>> "Changes the size of table where external semaphores are registered. 
>> The size can only grow, and will always be the next power of two larger than the parameter.
>> 
>> Setting this at any time other than start-up can potentially lose requests.
>> i.e. during the realloc new storage is allocated,
>> the old contents are copied and then pointers are switched. 
>> Requests occurring during copying won't be seen if they occur to indices already copied. 
>> The intended use is to set the table to some adequate maximum at start-up"
>> 
>> - self isRunningCog ifFalse: [^0].
>> "The vm-header field is a short, maximum 64k entries. Well, on most platforms anyways "
>> (aSize < 0 or: [aSize > 16rFFFF]) ifTrue: [^self error: 'maxExternalSemaphores: is limited to 16rFFFF'].
>> + ^[self vmParameterAt: 49 put: aSize] on: Error do: [0].!
>> - ^self vmParameterAt: 49 put: aSize!
>> 
>> Item was changed:
>> ----- Method: SmalltalkImage>>processPreemptionYields (in category 'system attributes') -----
>> processPreemptionYields
>> "Answer whether the VM causes a process to yield on process preemption,
>> i.e. to put a preempted process at the back of its run queue. If the parameter
>> is unavailable (non-Cog VMs) or bit 2 (4) is 0 then preemption yields."
>> 
>> + ^((self vmParameterAt: 48 default: [^true]) allMask: 4) not
>> + !
>> - ^(([self vmParameterAt: 48]
>> - on: Error
>> - do: [:ex| ^true]) allMask: 4) not!
>> 
>> Item was changed:
>> ----- Method: SmalltalkImage>>sendMouseWheelEvents (in category 'system attributes') -----
>> sendMouseWheelEvents
>> "The Cog VM can be instructed to deliver mouse wheel events as mouse wheel events.
>> By default mouse wheel events are mapped to arrow events.
>> This flag persists across snapshots, stored in the image header."
>> 
>> + ^(self vmParameterAt: 48 default: 0) anyMask: 32!
>> - ^(self vmParameterAt: 48) anyMask: 32!
>> 
>> Item was changed:
>> ----- Method: SmalltalkImage>>supportsMultipleBytecodeSets (in category 'system attributes') -----
>> supportsMultipleBytecodeSets
>> "Answer whether the VM supports multiple bytecodeSets."
>> "SmalltalkImage current supportsMultipleBytecodeSets"
>> 
>> + ^(self vmParameterAt: 65 default: nil)
>> - ^(self vmParameterAt: 65)
>> ifNil: [false]
>> ifNotNil:
>> [:param| "In older VMs this is a boolean answering the vm-internal MULTIPLE_BYTECODE_SETS define"
>> param isInteger "In newer VMs it is a set of integer flags, bit 0 of which is the vm-internal MULTIPLE_BYTECODE_SETS define"
>> ifTrue: [param anyMask: 1]
>> ifFalse: [param]]!
>> 
>> Item was changed:
>> ----- Method: SmalltalkImage>>supportsQueueingFinalization (in category 'system attributes') -----
>> supportsQueueingFinalization
>> "Answer whether the VM queues individual weak arrays for finalization, instead
>> of signalling the finalization semaphore once for all arrays and having the
>> WeakRegistry mechanism finalize all weak arrays, whether they need to or not."
>> "SmalltalkImage current supportsQueueingFinalization"
>> 
>> + ^(self vmParameterAt: 48 default: 0) anyMask: 16!
>> - ^(self vmParameterAt: 48) anyMask: 16!
>> 
>> Item was changed:
>> ----- Method: SmalltalkImage>>supportsReadOnlyObjects (in category 'system attributes') -----
>> supportsReadOnlyObjects
>> "Answer whether the VM observes the per-object read-only flag and consequently aborts
>> writes to inst vars of, and fails primitives that attempt to modify, read-only objects."
>> "SmalltalkImage current supportsReadOnlyObjects"
>> 
>> + ^(self vmParameterAt: 65 default: nil)
>> - ^(self vmParameterAt: 65)
>> ifNil: [false]
>> ifNotNil:
>> [:param| "In older VMs this is a boolean answering the vm-internal MULTIPLE_BYTECODE_SETS define"
>> param isInteger "In newer VMs it is a set of integer flags, bit 1 of which is the vm-internal IMMUTABILITY define"
>> ifTrue: [param anyMask: 2]
>> ifFalse: [false]]!
>> 
>> Item was added:
>> + ----- Method: SmalltalkImage>>vmParameterAt:default: (in category 'vm parameters') -----
>> + vmParameterAt: parameterIndex default: defaultValueOrBlock
>> + "Answer a VM parameter or defaultValueOrBlock value if out of range."
>> + 
>> + ^defaultValueOrBlock value!
>> 
>> Item was changed:
>> ----- Method: SmalltalkImage>>wordSize (in category 'image') -----
>> wordSize
>> "Answer the size in bytes of an object pointer or word in the object memory.
>> The value does not change for a given image, but may be modified by a SystemTracer
>> when converting the image to another format. The value is cached in WordSize to
>> avoid the performance overhead of repeatedly consulting the VM."
>> 
>> "Smalltalk wordSize"
>> 
>> + ^ WordSize ifNil: [WordSize := self vmParameterAt: 40 default: 4]!
>> - ^ WordSize ifNil: [WordSize := [self vmParameterAt: 40] on: Error do: [4]]!
>> 
>> 
> 
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