Smalltalk/X Webserver

Documentation of class 'Process':

Class: Process

Inheritance
Description
Class protocol
Instance protocol
Examples

Inheritance:

   Object
   |
   +--Link
      |
      +--Process
         |
         +--OSProcess::ShufflerProcess

Package:: stx:libbasic

Category:: Kernel-Processes

Version:: rev: 1.277 date: 2023/12/15 16:58:15; user: stefan; file: Process.st directory: libbasic; module: stx stc-classLibrary: libbasic

Description:

WARNING:
the offsets of the instance variables lookupActivations and lookupDisabled are known in the VM
do not remove them, and do not insert/remove instance variables before them

Instances of Process represent lightweight smalltalk processes
(i.e. threads). These all run in a shared smalltalk/X address space,
and can thus access and communicate via any objects.
Do not confuse these with (heavy-weight) unix processes, which are
created differently, and do NOT run in the same address space.
Also notice, that heavy-weight process creation takes much longer.
(see OperatingSystemclass>>fork).

Smalltalk processes do not necessarily need to be implemented as native
threads - it may, but the actual implementation depends on the underlying
OS's features. However, even if implemented as native thread, the ST/X
kernel makes certain, that only one thread executes at a time (with certain,
well-defined exceptions). The reason is that the required locking in the
runtime system would make things slower in most cases.

Processes are typically created by sending #fork or #forkAt: to a block;
the block creates a new process, defines itself as its startBlock,
and (optionally) tells the Processor about the new process.

Scheduling is done by Processor, which is the sole instance of ProcessorScheduler.
In ST/X, the scheduling algorithms are fully implemented (and visible) on the
smalltalk level - beside the threadSwitch primitive, there is virtually no VM
support (i.e. it can be easily changed).

Processes can be terminated either soft or via a hardTerminate.

A soft terminate (see Process>>terminate) will raise a TerminationSignal
in the process, which can be handled by the process.
If no other handler was specified, the processes own handler
(see Process>>start) will catch the signal and terminate the process.
During this signal processing, normal unwind processing takes place,
this means that with a soft terminate, all valueOnUnwind:/valueNowOrOnUnwind:
cleanup blocks are evaluated.
(so a process which has set up those blocks correctly does not have to
care especially about cleanup in case of termination).
Other than that, the TerminateSignal can be caught for special cleanup or
even to make the process continue execution.
If the process is suspended at termination time, it will be resumed
in order to perform its cleanup actions (i.e. the cleanup is always
done in the context of the terminating process itself).

A hard terminate (Process>>terminateNoSignal) will NOT do all of the above,
but quickly (and without any cleanup) terminate the process.
The debugger offers a quickTerminate option on its popupMenu for
situations, when soft termination fails. (for example, if some error was
coded into a handler or unwind block).

Leaving the processes startBlock has the same effect as a soft-terminate
(i.e. there is no need to send an explicit terminate).

Notice:
in Smalltalk/X, processes are gone, when an image is restarted;
this means that you have to take care of process re-creation yourself.
Usually, this is done by depending on ObjectMemory, recreating the
process(es) when the #returnFromSnapshot-change notifiction arrives.

All views (actually windowGroups) recreate their window process
on image-restart. You have to do so manually for your own processes.

A later version will allow specification of automatic restart, but
that's not yet implemented. However, even when implemented, restartable processes
will be recreated to restart from the beginning. It will not be possible to
automatically continue a processes execution where it left off.
This is a consequence of the portable implementation of ST/X, since in order to
implement process continuation, the machines stack had to be preserved and
recreated. Although this is possible to do (and actually not too complicated),
this has not been implemented, since the machines stack layout is highly machine/compiler
dependent, thus leading to much bigger porting effort of ST/X (which conflicts
with ST/X's design goal of being highly portable).

Process synchronization:
Synchronization with cooperating processes is supported as usual,
via Semaphores (see Semaphore, Delay, SharedQueue etc.)

With uncooperative processes, only synchronization on suspend
and termination is possible:
any other process can wait for a process to suspend or terminate.
This waiting is implemented by using suspendSemaphore and exitBlocks
(where an exitSemaphore is signalled).
See waitUntilSuspended / waitUntilTerminated.

Implementation note:
for historic and compatibility reasons, Process is a subclass of Link,
which means, that instances are directly usable as nodes in a linkedList.
However, this also means that processes can only be elements of a single LinkedList.
This is somewhat dangerous, as unknowledgable programmers may unwillingly break the
scheduler, by placing a process onto another linked list.
Therefore, we plan to change this in the future.

Process states:
#dead process has (been) terminated;
the process instance has no underlying
thread.

#run the process is willing to run,
but not active (i.e. another higher prio
process is currently executing)

#active the process is the current process
(there is only one)

#ioWait waiting on some io-related semaphore
(typically in #readWait / #writeWait)

#eventWait waiting on some GUI event

#timeWait waiting on a timer-related semaphore

#wait waiting on some (other) semaphore

#suspended stopped from execution; however, an interrupt
will return it into the run state.

#stopped stopped from execution; an interrupt will
NOT return it into the run state (for debugging)

#debug debugger sitting on top of the processes
stack.

Win32 only:

#osWait waiting on an OS-API call to finish.
can be interrupted, terminated and aborted
(i.e. the usual context actions are possible).

#halted thread was caught while in a blocking API call
or primitive endless loop and has been halted by
the scheduler.
Can only be resumed or hard-terminated - abort
or soft terminate or unwind actions are not possible.
(due to win32 limitations)

[Instance variables:]

id <SmallInteger> a unique process-id

creatorId <SmallInteger> the id of the process that
created me (useful for debugging
or monitoring).

processGroupId usually the id of the creator,
unless the process detached from
the group and became a groupLeader.
Groups can be easily terminated
as a whole.
Group leaders have a groupId of nil.
A groupId of 0 (zero) marks a system
process; these do not prevent a standAlone
app from exiting.

prio <SmallInteger> the processes priority

priorityRange <Interval> the processes dynamic priority range
(or nil)

state <Symbol> the processes state
(for process-monitor)

startBlock <Block> the startup-block (the one that forked)

name <String-or-nil> the processes name (if any)
(for process-monitor)

suspendSemaphore <Semaphore> triggered when suspend (if nonNil)

restartable <Boolean> is restartable; if true, the process
will be restarted when an image is
restarted. Otherwise, it remains dead.
Running processes cannot be continued
at the point where leftOff after an
image-restart.

interruptActions <Collection> interrupt actions as defined by interruptWith:,
performed at interrupt time

exitActions <Collection of Block>
additional cleanup actions to perform
on termination (if nonEmpty)

emergencySignalHandler <Block> can be used for per-process
emergency signal handling

interruptsDisabled <Boolean> flag if interrupts (as installed
via #interruptWith:) are currently
disabled. (i.e. on-hold).
Interrupts will be delivered when
reenabled.

exceptionHandlerSet <ExceptionhandlerSet>
Handled by any process; allows for
exceptionHandlers and query-answerers to
be added/removed dynamically.

[Class variables:]

TerminateSignal <Signal> signal used to terminate processes
(should not be caught - or at least
rejected in handlers).
If caught and proceeded, a process
cannot be terminated via #terminate.
For hardTermination (in case of emergency),
send it a #erminateNoSignal message.

RestartSignal <Signal> signal used to restart a process.
Can be caught in additional handler(s),
to perform all kind of re-initialization.
However, these handlers should reject,
for the restart to be really performed.

This software is furnished under a license and may be used
only in accordance with the terms of that license and with the
inclusion of the above copyright notice. This software may not
be provided or otherwise made available to, or used by, any
other person. No title to or ownership of the software is
hereby transferred.

Class protocol:

Signal constants

restartSignal: return the signal used for process restart
terminateSignal: return the signal used for process termination

defaults

defaultMaximumStackSize

return the default max stack size. All new processes get
this limit initially.
It may be changed for individual processes with:
aProcess setMaximumStackSize:limit

Usage example(s):

     Process defaultMaximumStackSize

defaultMaximumStackSize: numberOfBytes

set the default max stack size, return the previous value.
All new processes get this stack limit initially.
It may be changed for individual processes with:
aProcess setMaximumStackSize:limit
Notice:
There is seldom any need to change the default setting,
except for highly recursive programs.

Usage example(s):

     Process defaultMaximumStackSize:500*1024

wrapStackSize

return the wrap stack size.
Under windows, blocking API calls are executed on a separate stack with this size.
If you ever encounter that a call to n external library function requires more stack than
this, you may change this size in your startup (or programmatically) during early startup.
Returns nil on non-windows machines.

wrapStackSize: newSize

set the wrap stack size.
Under windows, blocking API calls are executed on a separate stack with this size.
If you ever encounter that a call to n external library function requires more stack than
this, you may change this size in your startup (or programmatically) during early startup.
An argument of 0 changes the size back to the default.
Returns the previous size.

initialization

initialize: (comment from inherited method)
called only once - initialize signals

instance creation

for: aBlock priority: aPrio: create a new (unscheduled) process which will execute aBlock at
a given priority, once scheduled. The process will start execution once
it gets a #resume-message.
new: create a new (unscheduled) process which will execute the start
method, when scheduled. The process will start execution once
it gets a #resume-message.

instance retrieval

findProcessWithId: id: return a process with a particular id.
This is only a debugging helper, to allow
easy access of a process by name in the MiniDebugger.
Do not use - ask Processor instead!

** This is an obsolete interface - do not use it (it may vanish in future versions) **
findProcessWithName: name: return a process with a particular name.
This is only a debugging helper, to allow
easy access of a process by name in the MiniDebugger
Do not use - ask Processor instead!

** This is an obsolete interface - do not use it (it may vanish in future versions) **
findProcessesWithGroupId: aGroupId: return a collection of processes with the particular group id.
Do not use - ask Processor instead!

** This is an obsolete interface - do not use it (it may vanish in future versions) **

Instance protocol:

Compatibility-Squeak

isTerminated
( an extension from the stx:libcompat package ): return true, if the receiver is a dead process

Compatibility-V'Age

queueInterrupt: aBlock
( an extension from the stx:libcompat package ): VisualAge compatibility: alias for #interruptWith:
arrange for the receiver process to be interrupted and
evaluate aBlock in its interrupt handler.

accessing

beGUIProcess: mark the receiver as a gui process.
This is currently not used, but allows end-user applications
to terminate all subprocesses which are GUI related, and leave
other background processes in the same process group untouched.
beGroupLeader: make the receiver a processGroupLeader.
This detaches the process from its creator, so that it will not
be terminated when it terminates via #terminateGroup.
Also, processes forked from a groupLeader belong to that group
and can be terminated via #terminateGroup - unless they become
group leaders themself.
(windowgroup processes do this).
beSystemProcess: make the receiver a system process.
These processes have a groupId of 0.
When executed as standAlone application, smalltalk exits when
no more user processes are running.
(i.e. when there are only systemProcesses left)
To prevent any daemon processes from preventing this exit,
you should make them systemProcesses
changePriority: aNumber: same as priority:, but returns the old priority.
(cannot do this in #priority: for ST-80 compatibility)
creatorId: return the process creator's id.
This has no semantic meaning, but is useful to identify processes
when debugging.
exceptionHandlerSet: retrieve the exceptionHandlerSet, which includes the set of
exceptions which are caught by the process.
Initially being empty, this allows for default handlers to be
dynamically added/removed from the set of handled exceptions/queries.
id: return the processes id
interruptsDisabled
name: return the processes name
name: aString: set the processes name
priority: return the receiver's priority
priority: aNumber: set my priority
priorityRange: return my dynamic priority range
priorityRange: anInterval: change my dynamic priority range
processGroupId: return the processes processGroup id.
Normally, when created, a processes creator id is taken and used
as the processGroup id.
When #terminateGroup is sent to a process, the process and all of its
group members are terminated together.

Processes can detach themself from the process group to prevent being
killed when the parent terminates (windowgroup processes do this).
processGroupId: aGroupLeadersProcessID: set the processes processGroup id.
Normally, when created, a processes creator id is taken and used
as the processGroup id.
When #terminateGroup is sent to a process, the process and all of its
group members are terminated together.

Processes can detach themself from the process group to prevent being
killed when the parent terminates (windowgroup processes do this).
restartable: aBoolean: set/clear, the restartable flag.
Restartable processes will automatically be restarted by the
ProcessorScheduler upon image restart.
Others have to be restarted manually.
setStateRun: set the state - only to be used from scheduler
singleStep: aBoolean
startBlock: return the processes startup-block
startTimestamp: return the processes' start time
state: return a symbol describing the processes state
state: aSymbol: set the state - only to be used from scheduler
suspendedContext: return the processes suspended context
- this is the context from which a process switch into the scheduler
or another process occurred.
For the active process, a dead process, or one which
had no chance to run yet, nil is returned.
Typically, only the debugger is interested in this one.

accessing-change notifications

addExitAction: aBlock: add aBlock to the processes exit actions.
This block will be evaluated right before the process dies,
and can be used to trigger actions somewhere else (i.e. synchronization).
addSuspendAction: aBlock: add aBlock to the processes suspend actions.
This block will be evaluated when a process gets suspended.
You may ask what that is useful for - it is useful to flush
buffered graphic commands of a GUI process (i.e. to force xlib
to send buffered commands to the display).
emergencySignalHandler: return the emergencySignalHandler block.
See Signal>>documentation for more info.
emergencySignalHandler: aOneArgBlock: set the emergencySignalHandler block.
See Signal>>documentation for more info.
removeAllExitActions: remove all exit actions.
removeAllSuspendActions: remove all suspend actions.
removeExitAction: anExitAction ifAbsent: exceptionBlock: remove the identical exitAction; if found, remove and return it;
if not, return the value from evaluating exceptionBlock
terminateActionBlock: aBlock: for compatibility with OSProcess,
this adds a block to be called when the process terminates

accessing-stack

maximumStackSize: returns the processes stack limit - i.e. the process will be
interrupted with a recursionSignal-raise, if it ever
needs more stack (in bytes) than this number
setMaximumStackSize: limit: sets the processes stack limit - i.e. the process will be
interrupted with a recursionSignal-raise, if it ever
needs more stack (in bytes) than this number.
Returns the old value.
setStackInitialSize: initial increment: increment safe: safe: hook for fine-tuning. Sets the processes initialStackSize- and
and stackIncrement-parameters. Not for normal use.

inspecting

inspectorExtraMenuOperations
( an extension from the stx:libtool package ): extra operation-menu entries to be shown in an inspector.
Answers a collection of pairs containing aString and action aBlock.
aString is the label of the menu item.
aBlock is evaluated when the menu item is selected.
raiseDebuggerOfProcess
( an extension from the stx:libtool package ): raise the debugger window, which is debugging me - if any

interrupts

blockInterrupts

disable interrupt processing for the receiver process
- if disabled, incoming interrupts will be registered and handled as
soon as interrupts are reenabled via unblockInterrupts.
Returns the previous blocking status i.e. true if interrupts
where already blocked. You need this information for proper
unblocking, in case of nested block/unblock calls.
This is similar to OperatingSystem>>blockInterrupts, but only
affects interrupts for the receiver process
(i.e. those which are installed via #interruptWith:)

Usage example(s):

     |p1|

     p1 := [
	     Transcript showCR:'disabled ...'.
	     Transcript showCR:Processor activeProcess blockInterrupts.
	     Transcript showCR:'busy ...'.
	     Delay waitForSeconds:10.
	     Transcript showCR:'enabled ...'.
	     Processor activeProcess unblockInterrupts.
	   ] forkAt:9.

     p1 interruptWith:[Transcript showCR:'interrupted'].

hasInterruptActions

return true, if there are any interrupt actions to evaluate
(i.e. if the receiver has been interrupted).

interruptWith: aBlock

interrupt the receiver and make it evaluate aBlock.
If the receiver is currently suspended it is resumed.
NOTE: the process (i.e. the receiver) will only perform the block immediately,
IFF its priority is higher than the priority of the currently running process.
Otherwise, it will remain suspended, until its time comes.

aBlock is evaluated with an optional argument: the context, that has been interrupted.

Usage example(s):

      |p|

      p := [
               [
                   10 timesRepeat:[
                       Delay waitForSeconds:0.5.
                       Transcript showCR:'looping...'
                   ]
               ] ensure:[
                   Transcript showCR:'aborted'
               ]
           ] fork.
      Delay waitForSeconds:2.
      p interruptWith:[:interruptedContext|
        Transcript showCR:e'interrupted ctx={interruptedContext}'
      ].
      Delay waitForSeconds:2.
      p interruptWith:[ AbortOperationRequest raise ].

Usage example(s):

you cannot interrupt an already finished thread..

     |p|

     p := [] fork.
     p waitUntilTerminated.
     p interruptWith:[Transcript showCR:Processor activeProcess].

onResumeDo: aBlock

prepare for the receiver to evaluate aBlock when resumed.
This is like #interruptWith:, but does not resume the receiver
(i.e. it continues its sleep).
This is useful to place a breakpoint on a sleeping process, to be fired
when it awakes.

stepInterruptHandler

get the handler for stepInterrupts occurring in the receiver process.
This is an interface for the debugger and allows it to monitor a threads
stepInterrupts. Returns the previous handler.
Not for general use.

Usage example(s):

     Processor activeProcess stepInterruptHandler

stepInterruptHandler: anObject

set the handler for stepInterrupts occurring in the receiver process.
This is an interface for the debugger and allows it to monitor a threads
stepInterrupts. Returns the previous handler.
Not for general use.

unblockInterrupts

enable interrupt processing for the receiver process
- if any interrupts are pending, these will be handled immediately.
When unblocking interrupts, take care of nested block/unblock
calls - you should only unblock after a blockcall if they where
really not blocked before.
This is similar to OperatingSystem>>unblockInterrupts, but only
affects interrupts for the receiver process
(i.e. those which are installed via #interruptWith:)

interrupts-private

addInterruptAction: aBlock asFirstAction: aBoolean: make the receiver evaluate aBlock when resumed/interrupted.
The name is somewhat misleading (actually, its historic):
the block is also evaluated on resume.
With asFirstAction, if another interrupt action is already pending,
aBlock will be executed first (to allow interrupting a debugged thread).
evaluateInterruptActionsWithContext: aContext: evaluate my interrupt-actions.
forceInterruptOnReturnOf: aContext: helper entry for debugger. Force a stepInterrupt whenever aContext
returns either directly or via an unwind.
interrupt: evaluate my interrupt-actions.
The process will go back to where it got interrupted
after doing this.

This is also sent by the VM.
interruptedIn: aContext: evaluate my interrupt-actions.
This is indirectly called by the VM, when some #interruptWith: action
was scheduled for the process, and the process is resumed.
The process will go back to where it got interrupted after doing this.

monitoring

numberOfStackBoundaryHits: internal monitoring only - will vanish
numberOfStackSegments: return the processes number of stack segments currently used.
This method is for monitoring purposes only - it may vanish.
totalStackSize: return the processes maximum used stack size.
This method is for monitoring purposes only - it may vanish.
usedStackSize: Return the processes current stack size.
This method is for monitoring purposes only - it may vanish.
vmTrace: aBoolean: turn on/off VM message tracing for the receiver.
This is meant for ST/X debugging, and may vanish.
Expect lots of output, once this is turned on.

obsolete

exitAction: aBlock: Obsoleted by addExitAction: / removeAllExitActions.

Add aBlock to the processes exit actions.
This block will be evaluated right before the process dies.
An argument of nil removes all exitActions.

** This is an obsolete interface - do not use it (it may vanish in future versions) **
suspendAction: aBlock: Obsoleted by addSuspendAction: / removeAllSuspendActions.

Add aBlock to the processes suspend actions.
This block will be evaluated when a process gets suspended.
A nil argument removes all suspendActions.

** This is an obsolete interface - do not use it (it may vanish in future versions) **
terminateAllSubprocesses: ** This is an obsolete interface - do not use it (it may vanish in future versions) **
terminateWithAllSubprocesses: ** This is an obsolete interface - do not use it (it may vanish in future versions) **

printing & storing

printOn: aStream: a little more info in my printed representation

private

for: aBlock priority: aPrio: setup the new process - the receiver is not scheduled for
execution, to get it running, send it #resume

private-scheduler access

setId: idNumber state: stateSymbol: set id and state - not for public use
setPriority: aNumber: set priority without telling processor - not for public use
setPriorityRange: anInterval: set priority without telling processor - not for public use
setStartBlock: aBlock: set the receiver's startup block
setStateTo: newState if: oldState
setStateTo: newState if: oldState1 or: oldState2

queries

isActive

return true if I am the active process

isAlive

return false, if the receiver is a dead process

isDead

return true, if the receiver is a dead process

isDebugged

return true, iff the receiver process is currently being debugged
(i.e. is stopped and a debugger sits on top of it)

isDebuggedOrStopped

return true, iff the receiver process is currently being stopped
and possibly debugged (i.e. is stopped and a debugger sits on top of it)

isDebuggerProcess

return true, iff the receiver process is currently running a Debugger or
an Inspector. Senders may behave differently and e.g. timeout on
endless blocking operations.

isGUIProcess

return true, if this is a GUI process.
I.e. a windowGroup process.
This is currently not used, but allows end-user applications
to terminate all subprocesses which are GUI related, and leave
other background processes in the same process group untouched.

isRestartable

return true, iff the receiver is restartable

isRunning

return true, iff the receiver is running (state == #run);
this does not mean that it is currently active
(it might be suspended by the current process)

isSingleStepping

isStopped

return true, iff the receiver is stopped

isSystemProcess

return true if aProcess is a system process,
which should not be suspended/terminated etc..

isUserProcess

return true if aProcess is a user process.

nameOrId

return a string to identify the process - either name or id

parentProcess

answer my parent.
Notice: we do only keep the id here, to prevent the parentProcess from being
referenced (and therefore not garbage collected if it terminates)

Usage example(s):

     Processor activeProcess parentProcess

processGroupLeader

answer the parent of this process group

Usage example(s):

      Processor activeProcess processGroupLeader

special

externalLookupPopIfEqual: lookupObject

Called by method lookup MOP when an lookup context is to be unwound
to cleanup lookup stack

millisecondDelay: millis

suspend the current process for some time.
Attention:
If the receiver is a system process (i.e. scheduler or event dispatcher)
this blocks the whole Smalltalk for the time delta;
if it's a normal thread, only that thread is suspended.

trapRestrictedMethods: trap

Allow/deny the execution of restricted methods.
Process specific method restriction is not implemented yet, so this call is
redirected to ObjectMemory and causes a system wide restriction.

Notice: method restriction is a nonstandard feature, not supported
by other smalltalk implementations and not specified in the ANSI spec.
This is EXPERIMENTAL - and being evaluated for usability.
It may change or even vanish (if it shows to be not useful).

Usage example(s):

	Processor activeProcess trapRestrictedMethods:true
	Processor activeProcess trapRestrictedMethods:false

uninterruptablyDo: aBlock

execute aBlock with interrupts blocked.
This does not prevent preemption by a higher priority processes
if any becomes runnable due to the evaluation of aBlock
(i.e. if a semaphore is signalled there).

waitUntilSuspended

wait until the receiver is suspended.

waitUntilTerminated

wait until the receiver is terminated.
This method allows another process to wait till the receiver finishes.

Usage example(s):

     |p|

     p := [100 timesRepeat:[1000 factorial]] forkAt:4.

     Transcript showCR:'now waiting ...'.
     p waitUntilTerminated.
     Transcript showCR:'done.'

waitUntilTerminatedWithTimeout: secondsOrNilOrTimeDuration

wait until the receiver is terminated or (if non-nil) until
the time period exired.
Returns true if a timeout occurred.
This method allows another process to wait until the receiver finishes
(optionally) within some time.

Usage example(s):

     |p|

     p := [10 timesRepeat:[10000 factorial]] forkAt:4.

     Transcript showCR:'now waiting ...'.
     (p waitUntilTerminatedWithTimeout:2) ifTrue:[
         Transcript showCR:'timeout occurred.'
     ]

withHigherPriorityDo: aBlock

execute aBlock at a higher priority.

Usage example(s):

     Processor activeProcess withHigherPriorityDo:[3000 factorial]

withLowerPriorityDo: aBlock

execute aBlock at a lower priority. This can be used to perform
time-consuming operations at a more user-friendly priority.

Usage example(s):

     Processor activeProcess withLowerPriorityDo:[3000 factorial]

withPriority: aPrio do: aBlock

execute aBlock at another priority. This can be used to perform
time-consuming operations at a more user-friendly priority,
or some critical action at a higher priority. Do not use too high
of a priority to avoid locking up the system (event processing takes place
at 24)

Usage example(s):

     Processor activeProcess withPriority:7 do:[3000 factorial]

Usage example(s):

be careful - even ^C wont work until done:
     Processor activeProcess withPriority:25 do:[3000 factorial]

withPriority: lowPrio to: highPrio do: aBlock

execute aBlock at a priority range. This can be used to perform
time-consuming operations at a more user-friendly priority,
or some critical action at a higher priority. Do not use too high
of a priority to avoid locking up the system (event processing takes place
at 24)

Usage example(s):

     Processor activeProcess withPriority:7 to:8 do:[3000 factorial]

withSystemBackgroundPriorityDo: aBlock

execute aBlock at system background priority.
This can be used to perform
background operations at a more user-friendly priority.

Usage example(s):

     Processor activeProcess withSystemBackgroundPriorityDo:[3000 factorial]

withUserBackgroundPriorityDo: aBlock

execute aBlock at background priority. This can be used to perform
time-consuming operations at a more user-friendly priority.

Usage example(s):

     Processor activeProcess withUserBackgroundPriorityDo:[3000 factorial]

start & stop

imageRestart

restart the process from the beginning.
This is sent by the ProcessorScheduler at image restart time,
to all restartable processes.

restart

restart the process from the beginning.
This is only possible, if it's restartable.

start

start the process - this is sent by the VM to the process to get
the process up and running.
Sending #start to the process (instead of directly executing the startBlock)
allows more flexible handling of processes, since anything that responds
to #start can be handled transparently by the VM then ...

Usage example(s):

save block for possible restart

Usage example(s):

startBlock := nil

terminate

terminate the receiver process.
Termination is done by raising the terminateSignal in the receiver process,
which can be caught.
If the process is stopped, it will be resumed so that it can die.
All unwind actions and the exit-actions (if any)
will be performed before the process is really terminated.
Notice, that the terminate actions are performed by the receiver,
at its current priority. Therefore, in case higher prio processes are
running, it may take any arbitrary time until the termination is eventually
done.

terminateAllGUISubprocesses

terminate all the receiver's gui subprocesses and their children as well
(i.e. all processes which are offsprings of the receiver, except for
the receiver itself).

terminateAllSubprocessesInGroup

terminate all subprocesses which have the receiver process as groupID,
and their group-children as well.
That is all processes which have been directly or indirectly created
by the current process
(i.e. all processes in the receiver's process group, except for the receiver itself,
and recursively all of their group processes).

terminateAllSubprocessesInGroup: aGroup

terminate all subprocesses which have aGroup as groupID,
and their group-children as well
(i.e. all processes in the receiver's process group, except for the receiver itself,
and recursively all of their group processes).

terminateGroup

terminate the receiver with all of its created subprocesses
that are in the receiver's process group.

terminateNoSignal

hard-terminate the receiver process without sending a terminateSignal
or performing any unwind-handling.
However, exit-actions are performed.
This is useful in case of emergency, when a buggy terminationHandler
prevents you from getting a process to terminate.
Processes always perform this method when terminating - either normally or abnormally.

terminateSubprocesses

terminate all the receiver's subprocesses
(i.e. all processes in the receiver's process group, except for
the receiver itself).

terminateWithAllGUISubprocesses

terminate the receiver with all of its created gui subprocesses and their gui children.

terminateWithAllSubprocessesInGroup

terminate the receiver with
all subprocesses which have the receiver's process ID as groupID,
and their group-children as well.
(i.e. the receiver plus all processes in the receiver's process group,
and recursively all of their group processes).

terminateWithException: aTerminateException

terminate the receiver process.
Termination is done by raising aTerminateException in the receiver process,
which can be caught.
If the process is stopped, it will be resumed so that it can die.
All unwind actions and the exit-actions (if any)
will be performed before the process is really terminated.
Notice, that the terminate actions are performed by the receiver,
at its current priority. Therefore, in case higher prio processes are
running, it may take any arbitrary time until the termination is eventually
done.

suspend & resume

abort: raise an AbortOperationRequest in the receiver process.
Most processes willing to handle this will return to some save state
(typically, some kind of event loop).
If not handled, this will result in termination of the process.
resume: resume the receiver process
resumeForSingleSend: resume the receiver process, but only let it execute a single send.
stop: suspend the receiver process - will continue to run when a resume is sent.
A stopped process will not be resumed for interrupt processing.
suspend: suspend the receiver process - it will continue to run when a resume is sent.
Notice, that an interrupt will also resume the receiver,
so any waiting code should be prepared for premature return from
a suspend (see wait code in Semaphore).
Use #stop for a hard-suspend, which is not affected by interrupts.
suspendWithState: aStateSymbol: like suspend, this suspends the receiver process until a resume is sent.
This sets the state to the argument, aStateSymbol, which is shown
in the ProcessMonitor (instead of #suspended).
(i.e. no new functionality, but a bit more debuggability)
Notice, that an interrupt will also resume the receiver,
so any waiting code should be prepared for premature return from
a suspend (see wait code in Semaphore).
Use #stop for a hard-suspend, which is not affected by interrupts.
Should be called with interrupts disabled.

thread local storage

environment

return the dictionary holding thread local variables, or nil if there are none

environment: aDictionary

set the dictionary holding thread local variables, or nil if there are to be none

environmentAt: aKey

return the value of a thread local variable, or raise an error, if no such variable exists

environmentAt: aKey ifAbsent: aBlock

return the value of a thread local variable, or the value of defaultValue if no such variable exists

environmentAt: aKey put: aValue

set the value of a thread local variable. Returns aValue

environmentIncludesKey: aKey

true if there is a thread local variable, false if no such variable exists

stderr

the processes stderr.
By default, this is Stderr, but it can be overwritten
(for example to redirect a thread's error output to some other place

Usage example(s):

     Processor activeProcess stderr

stdin

the processes stdin.
By default, this is Stdin, but it can be overwritten
(for example to redirect a thread's input from some other place

stdout

the processes stdout.
By default, this is Stdout, but it can be overwritten
(for example to redirect a thread's output to some other place

threadVariableValueOf: aKey

return the value of a thread local variable,
or nil if no such variable exists

transcript

the processes transcript.
By default, this is Transcript, but it can be overwritten
(for example to redirect a thread's output to some other place

withThreadLocalVariables: aDictionary do: aBlock

evaluate a block with threadLocalVariables from aDictionary;
restore the old bindings afterwards.

withThreadVariable: variableNameSymbol boundTo: aValue do: aBlock

evaluate a block with the threadLocalVariable being bound to aValue;
undo the variable binding afterwards.

Usage example(s):

     |printIt|

     printIt := [
		    Transcript
			showCR:'foo is now ',
			(Processor activeProcess threadVariableValueOf:#foo) printString
		].

     Processor activeProcess
	 withThreadVariable:#foo
	 boundTo:1234
	 do:[
	    printIt value.
	    Processor activeProcess
		withThreadVariable:#foo
		boundTo:2345
		do:[
		    printIt value
		].
	    ]

Examples:

start a background process, computing 1000 factorial 100 times; the processes priority is set to not disturb any interactive process. Since its prio is higher than the 3D animation demos prio, you will notice, that those are suspended while the computation runs. But Interactive views (like browsers) will continue to react normal.

[
   'starting' printNL.
   100 timesRepeat:[1000 factorial].
   'done with factorial' printNL.
] forkAt:(Processor userBackgroundPriority).

start a background process, computing 1000 factorial 100 times; the processes priority is set to not disturb any process. The prio is set to 1 (which is the lowest possible) notice that now, the 3D animation demos also continue to run.

[
   'starting' printNL.
   100 timesRepeat:[1000 factorial].
   'done with factorial' printNL.
] forkAt:1.

start a background process, reading a pipe without blocking other processes;

[
   |p|

   'starting' printNL.
   p := PipeStream readingFrom:'ls -lR .'.
   [p atEnd] whileFalse:[
       p readWait.
       p nextLine printNL.
   ].
   p close.
   'done with pipe' printNL.
] forkAt:1.

see more examples in doc/coding (or search in the browser for senders of fork*)

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