[squeak-dev] The Trunk: System-cmm.725.mcz

Levente Uzonyi leves at elte.hu
Wed Jul 1 11:30:03 UTC 2015


Hi Eliot,

I reviewed the code and made a few changes, which you can find in the 
Inbox as System-ul.748. Feel free to pick the ones you like.
The change of Preferences class >> #atomicUpdatePreferences: might seem 
unnecessary, because it's so unlikely to have multiple processes 
changing the preferences concurrently.

Levente

P.S.: Please note that I haven't tested the code.

On Tue, 30 Jun 2015, Eliot Miranda wrote:

> Hi All, but especially Chris,
>    I just committed System-eem.745 to the inbox.  Please review.
> 
> As I say in the commit comment, this is step 1.  If the code looks OK, the next step is a version which moves the preferences dictionary into a class inst var, so that ServicePreferences sits happily below Preferences.  But for that I'll need advice on how to write the
> sequence of loads.  I *think* it's one configuration map and one package load.  The commit/configuration adds the class inst var and copies the DictionaryOfPreferences into it.  A subsequent commit replaces all methods that acess DictionaryOfPreferences and
> ServiceDictionaryOfPreferences with accesses to the class inst var
> 
> 
> Rewrite Preferences to eliminate the AccessProtect.
> Use a copy, update copy, assign scheme to update
> the preferences dictionary atomically.
> 
> Change Preferences access method compilation to
> use Object>>#value to eliminate a block creation.
> 
> Change Preference initialization to eliminate the
> isKindOf: Symbol.
> 
> This is step 1.  Given SystemPreferences it is clear
> that the preferences dictionary should be stored in
> a class inst var, so that SystemPreferences and
> Preferences can share methods but access different
> dictionaries.  The dictionaryOfProferences[:] accessors
> are dubious as they break encapsulatiopn.  For example,
> the reportPreferences: method, which is the only external
> access, could insateaqd be moved into Preferences class.
> 
> On Tue, Jun 30, 2015 at 10:46 AM, Eliot Miranda <eliot.miranda at gmail.com> wrote:
>       Hi Levente,  Hi Chris,
>
>       On Tue, Apr 28, 2015 at 3:41 PM, Levente Uzonyi <leves at elte.hu> wrote:
>             There's no need to store preferences in a data structure at all. We already have "pragma" preferences (since 4.1), which store the preference values independently. Since the 4.1 release it's a "permanent" goal to rewrite all preferences to
>             "pragma" preferences.
>             We should just make it happen.
> 
> 
> This seems like a lot of work, and is work that can be done over time.  But right now we're suffering lock ups due to the Mutex in Preferences.  For example, the Notifier/Debugger accesses the scrollBarsOnRight preference and I've often seen lock ups caused by
> this.  So I propose that I fix the access to be as I described it.  There be no access lock except for adding/updating preferences.  So reading is done without synchronisation, and setting and/or adding is done by copying and assigning.  I also propose to compile
> preferences without creating a block, so
> 
> autoIndent
> ^ self
> valueOfFlag: #autoIndent
> ifAbsent: true
> 
> instead of
> 
> autoIndent
> ^ self
> valueOfFlag: #autoIndent
> ifAbsent: [true]
> 
> which is well-supported by both the Interpreter and the Cog VMs, given Object>>value ^self.  This to save space and time.
>
>       Levente
>
>       P.S.: Reverting that method will solve the concurrency issue.
>
>       On Tue, 28 Apr 2015, Eliot Miranda wrote:
> 
> 
>
>             On Tue, Apr 28, 2015 at 12:47 PM, Chris Muller <asqueaker at gmail.com> wrote:
>                   Wait, the newer one has a non-local return in it, but
>                   Mutex>>#critical: has an ensure: in it anyway, so maybe I don't see
>                   the problem..?
> 
>
>             If one hits ctrl-period when the system is in the critical section then the debugger can't open because it interrupts the critical section, preventing the ensure block from running, attempts to access e.g.
>             scroll bar preferences when it tries to open, and the system deadlocks.  So preferences either need to be *not* protected by a critical section, or the Debugger needs not to access preferences.
>
>             IMO, we should try and write preferences so that they don't require a lock.  Writing them as a lock-free data structure would be a really good idea. First that critical section is slow and clunky.  Second, I
>             presume it is there only for the rare case of a write to preferences, not to protect reads.
>
>             IMO, a simple implementation which copied and replaced the entire preferences dictionary on write would be sufficient.  Sure there's a danger that some client would get a stale value if it read concurrently
>             while there was a write, but then so what?  A preference is a preference, not a hard-and-fast value, and code should work accessing a preference no matter its value, so momentarily getting a stale value
>             shouldn't matter.  So the implementation could be as simple as
>
>             addPreference: aName categories: categoryList default: aValue balloonHelp: helpString projectLocal: localBoolean changeInformee: informeeSymbol changeSelector: aChangeSelector type: aType
>             "Add or replace a preference as indicated.  Reuses the preexisting Preference object for this symbol, if there is one, so that UI artifacts that interact with it will remain valid."
>
>             | aPreference aPrefSymbol |
>             aPrefSymbol := aName asSymbol.
>             aPreference := DictionaryOfPreferences
>             at: aPrefSymbol
>             ifAbsent:
>             [| newPreference |
>             newPreference := aPreference 
>             name:aPrefSymbol
>             defaultValue:aValue
>             helpString:helpString
>             localToProject:localBoolean
>             categoryList:categoryList
>             changeInformee:informeeSymbol
>             changeSelector:aChangeSelector
>             type: aType.
>             AccessLock critical:
>             [| newDict |
>             newDict := DictionaryOfPreferences copy.
>             newDict at: aPrefSymbol put: newPreference].
>             self  compileAccessMethodForPreference:aPreference.
>             newPreference]
> 
>
>                   On Tue, Apr 28, 2015 at 2:43 PM, Chris Muller <asqueaker at gmail.com> wrote:
>                   >> The above change restores the old behavior of locking up the image, so it
>                   >> should be reverted. An additional comment explaininng why aBlock must not be
>                   >> evaluated inside the argument of #accessDictionaryOfPreferencesIn: would be
>                   >> helpful.
>                   >
>                   > Ahh, because aBlock might have a non-local return in it, leaving the
>                   > Mutex unsignaled (and critical unenterable), is that right?
>                   >
>                   > Took me a minute to see that problem.
>                   >
>                   > Okay, I'll revert that method if no one else does by my next commit..
>                   >
>                   >> It would be even better to finally get rid of DictionaryOfPreferences.
>                   >>
>                   >>
>                   >> Levente
>                   >>
> 
> 
> 
>
>             --
>             best,Eliot
> 
> 
> 
> 
> 
> 
> 
> --
> best,Eliot
> 
> 
> 
> 
> --
> best,Eliot
> 
>


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