digitalmars.D - Static destructors called before class instance destructors
- rkreis (48/48) Jul 21 2007 Good day.
- Sean Kelly (10/52) Jul 22 2007 Funny, I've recently been trying to decide how to handle this exact
- rkreis (10/66) Jul 22 2007 I vote against silently leaving them unfinalized just because they might...
- Tristam MacDonald (2/55) Jul 22 2007 DO they actually get finalised at the moment? I seem to have noticed tha...
- Sean Kelly (5/61) Jul 23 2007 Not in Tango right now, no. But I may at least perform a normal
Good day. Using derelict, I noticed bad behavior: The app segfaulted inside of destructors. I later found out that derelict unloaded libraries and the destructor, freeing resources, tried to call such unloaded functions. This happens because a static destructor unloads all libraries. A simple test case shows that static destructors can be called before all instances are destructed. If an instance destructor then uses resources freed by the static destructor, things become problematic. import std.stdio; class Dude { private static char[] eek; public this() { writefln("Dude ctor"); } public ~this() { writefln("Dude dtor - eek is '%s'", eek); } public static this() { writefln("Dude static ctor"); eek = "Everything up and running"; } public static ~this() { writefln("Dude static dtor"); eek = "You're doomed"; } } void main() { Dude d = new Dude(); } outputs Dude static ctor Dude ctor Dude static dtor Dude dtor - eek is 'You're doomed' with GDC 0.23 and DMD 1.018. This shows that the instance destructor accesses a static variable that has been modified by the static destructor. I can't think of any workaround. In my opinion, it would be better if static destructors were only called after all unreachable class instances have been destructed. That wouldn't break static destructors accessing static references to class instances. If one of those classes also depends on the static destructor not having run, that's a circular dependency to which I can't find a satisfying solution. For those cases, I suggest the current behavior, or a compile time error (which is hard to implement, I believe). Anyway, easily accessing static variables after the static destructor has run doesn't sound right. See you soon.
Jul 21 2007
rkreis wrote:Good day. Using derelict, I noticed bad behavior: The app segfaulted inside of destructors. I later found out that derelict unloaded libraries and the destructor, freeing resources, tried to call such unloaded functions. This happens because a static destructor unloads all libraries. A simple test case shows that static destructors can be called before all instances are destructed. If an instance destructor then uses resources freed by the static destructor, things become problematic. import std.stdio; class Dude { private static char[] eek; public this() { writefln("Dude ctor"); } public ~this() { writefln("Dude dtor - eek is '%s'", eek); } public static this() { writefln("Dude static ctor"); eek = "Everything up and running"; } public static ~this() { writefln("Dude static dtor"); eek = "You're doomed"; } } void main() { Dude d = new Dude(); } outputs Dude static ctor Dude ctor Dude static dtor Dude dtor - eek is 'You're doomed'Funny, I've recently been trying to decide how to handle this exact situation. When a D application shuts down, unreachable objects may/will be collected then static dtors are run. After that, there may still be valid D objects floating around, either which the GC incorrectly thought were reachable or that were reachable through static references. Should these objects never be finalized? This would certainly be the easier/cleaner approach to take, but I'm not sure how I feel about leaving objects un-finalized. Sean
Jul 22 2007
Sean Kelly schrieb:rkreis wrote:I vote against silently leaving them unfinalized just because they might depend on static variables. Maybe print a (runtime) warning or error (like unhandled switch cases), or just finalize them, making it the developer's job to care that objects still reachable after the static destructors have run won't depend on static variables. Either way, I would like all unreachable objects to be collected before static destructors are run. And I'd also like to see more opinions/suggestions on this. Have a nice dayGood day. Using derelict, I noticed bad behavior: The app segfaulted inside of destructors. I later found out that derelict unloaded libraries and the destructor, freeing resources, tried to call such unloaded functions. This happens because a static destructor unloads all libraries. A simple test case shows that static destructors can be called before all instances are destructed. If an instance destructor then uses resources freed by the static destructor, things become problematic. import std.stdio; class Dude { private static char[] eek; public this() { writefln("Dude ctor"); } public ~this() { writefln("Dude dtor - eek is '%s'", eek); } public static this() { writefln("Dude static ctor"); eek = "Everything up and running"; } public static ~this() { writefln("Dude static dtor"); eek = "You're doomed"; } } void main() { Dude d = new Dude(); } outputs Dude static ctor Dude ctor Dude static dtor Dude dtor - eek is 'You're doomed'Funny, I've recently been trying to decide how to handle this exact situation. When a D application shuts down, unreachable objects may/will be collected then static dtors are run. After that, there may still be valid D objects floating around, either which the GC incorrectly thought were reachable or that were reachable through static references. Should these objects never be finalized? This would certainly be the easier/cleaner approach to take, but I'm not sure how I feel about leaving objects un-finalized. Sean
Jul 22 2007
Sean Kelly Wrote:rkreis wrote:DO they actually get finalised at the moment? I seem to have noticed that a lot of destructors aren't run at program termination, unless fullCollect() is explicitly called.Good day. Using derelict, I noticed bad behavior: The app segfaulted inside of destructors. I later found out that derelict unloaded libraries and the destructor, freeing resources, tried to call such unloaded functions. This happens because a static destructor unloads all libraries. A simple test case shows that static destructors can be called before all instances are destructed. If an instance destructor then uses resources freed by the static destructor, things become problematic. import std.stdio; class Dude { private static char[] eek; public this() { writefln("Dude ctor"); } public ~this() { writefln("Dude dtor - eek is '%s'", eek); } public static this() { writefln("Dude static ctor"); eek = "Everything up and running"; } public static ~this() { writefln("Dude static dtor"); eek = "You're doomed"; } } void main() { Dude d = new Dude(); } outputs Dude static ctor Dude ctor Dude static dtor Dude dtor - eek is 'You're doomed'Funny, I've recently been trying to decide how to handle this exact situation. When a D application shuts down, unreachable objects may/will be collected then static dtors are run. After that, there may still be valid D objects floating around, either which the GC incorrectly thought were reachable or that were reachable through static references. Should these objects never be finalized? This would certainly be the easier/cleaner approach to take, but I'm not sure how I feel about leaving objects un-finalized. Sean
Jul 22 2007
Tristam MacDonald wrote:Sean Kelly Wrote:Not in Tango right now, no. But I may at least perform a normal collection prior to the static dtors to clean up all the stuff that really is no longer being referenced. Seanrkreis wrote:DO they actually get finalised at the moment? I seem to have noticed that a lot of destructors aren't run at program termination, unless fullCollect() is explicitly called.Good day. Using derelict, I noticed bad behavior: The app segfaulted inside of destructors. I later found out that derelict unloaded libraries and the destructor, freeing resources, tried to call such unloaded functions. This happens because a static destructor unloads all libraries. A simple test case shows that static destructors can be called before all instances are destructed. If an instance destructor then uses resources freed by the static destructor, things become problematic. import std.stdio; class Dude { private static char[] eek; public this() { writefln("Dude ctor"); } public ~this() { writefln("Dude dtor - eek is '%s'", eek); } public static this() { writefln("Dude static ctor"); eek = "Everything up and running"; } public static ~this() { writefln("Dude static dtor"); eek = "You're doomed"; } } void main() { Dude d = new Dude(); } outputs Dude static ctor Dude ctor Dude static dtor Dude dtor - eek is 'You're doomed'Funny, I've recently been trying to decide how to handle this exact situation. When a D application shuts down, unreachable objects may/will be collected then static dtors are run. After that, there may still be valid D objects floating around, either which the GC incorrectly thought were reachable or that were reachable through static references. Should these objects never be finalized? This would certainly be the easier/cleaner approach to take, but I'm not sure how I feel about leaving objects un-finalized. Sean
Jul 23 2007