Hi Levente,  Hi Chris,

On Tue, Apr 28, 2015 at 3:41 PM, Levente Uzonyi <leves@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@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@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