Wait, the newer one has a non-local return in it, but Mutext>>#critical: has an ensure: in it anyway, so maybe I don't see the problem..?

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

On Tue, Apr 28, 2015 at 5:00 PM, Levente Uzonyi leves@elte.hu wrote:

If there's an error signaled from aBlock, and the default error handler is activated (see UnhandledError >> #defaultAction), then the process will be suspended (see Debugger class >> #morphicOpenOn:context:label:contents:fullView:) while it's inside the AccessLock mutex's critical section. The (new) UI process will try to display a debugger. To do that, it will try to read the values of various preferences, but the suspended process is holding the mutex, so it'll wait forever. This results in an image lockup, because using Alt+. (Cmd+. on mac) will also try to open a debugger. This is why aBlock must be evaluated outside of the AccessLock mutex's critical section.

Okay, the newer one is probably safer because #at:ifPresent: *probably* won't get an error, but theoretically it still could, leaving the image locked for the very same reason.

So Eliots suggestion is sounding good -- why do something like preferences need to be guarded on access? It seems not that important...

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.

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

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

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@gmail.com wrote:

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

Hi Levente,

yes I like the repeat in atomicUpdatePreferences:. That's safe. I don't care much for the method temp in refEvent: cuz I think the message keyword types anEvent item adequately. Not sure about storePreferencesIn: not taking a copy of preferencesDictionary. Surely it's safer to take the copy. So let me take the change to atomicUpdatePreferences: and get this show on the road :-). Thanks for your review!

On Wed, Jul 1, 2015 at 4:30 AM, Levente Uzonyi leves@elte.hu wrote:

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@gmail.com wrote: 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

-- best,Eliot

Hi Eliot,

My change of #prefEvent: is not about the temporary variable. It's about removing the loop which got duplicated. The original method looked like

... method := anEvent item. method pragmas do:[:pragma| | aPreference aPrefSymbol | ((pragma keyword == #preference:category:description:type:) or: [pragma keyword == #preference:categoryList:description:type:]) ifTrue:[ aPrefSymbol := (aClass name,'>>', method selector) asSymbol. ...

Your version with #respondToPreferencePragmasInMethod:class: inlined would look like

... method := anEvent item. * method pragmas do: [:pragma| * method pragmas do: [:pragma| | preference | ((pragma keyword beginsWith: #preference:) and: [self respondsTo: pragma keyword]) ifTrue: [preference := self perform: pragma keyword withArguments: pragma arguments. ...

One of the "method pragmas do:" loops (marked with *) is superfluous. Since #respondToPreferencePragmasInMethod:class: contains the loop, and is also sent by other methods, I decided to remove the loop from #prefEvent:.

The #copy in #storePreferencesIn: was added in Squeak 4.1, or 4.2, because the dictionary could have been read and written concurrently. But this is not the case anymore.

Levente

On Wed, 1 Jul 2015, Eliot Miranda wrote:

Hi Levente,    yes I like the repeat in atomicUpdatePreferences:.  That's safe.  I don't care much for the method temp in refEvent: cuz I think the message keyword types anEvent item adequately.  Not sure about storePreferencesIn: not taking a copy of preferencesDictionary.  Surely it's safer to take the copy.  So let me take the change to atomicUpdatePreferences: and get this show on the road :-).  Thanks for your review!

On Wed, Jul 1, 2015 at 4:30 AM, Levente Uzonyi leves@elte.hu wrote: 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@gmail.com> wrote:
              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
                          >>




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                    best,Eliot







        --
        best,Eliot




        --
        best,Eliot

-- best,Eliot