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