Cannot evaluate expression because a thread is stopped at a point where garbage collection is impossible...

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# 1   June 20th, 2007, 05:00 PM

Mike Andrews Guest   Posts: n/a   Time spent in forums: Reputation Power:

PRB: Cannot evaluate expression because a thread is stopped at a point where garbage collection is impossible... Guys, I'm getting this in the VS2005 IDE when I try to debug my code. I'm really at a loss to figure this one out. "Cannot evaluate expression because a thread is stopped at a point where garbage collection is impossible, possibly because the code is optimized." This does not occur until a method with a particular line of code is entered. this method is entered by the debugger, any object more complex than the intrinsic data types such as ints and strings cause this error to be displayed. The methods are as such: //Variables are readable before this line this.GridHelper.MarContainer = new MarContainer(myGuid, ThirtyDay, this.GridHelper.StartDate); //And after this line public class GridHelper { public GridHelper(Guid guid, MarType type, DateTime date){ //Variables are readable before this line Load(guid, type, date, null); //But not after this line } private void Load(Guid guid, MarType type, DateTime startDate, TransactionContext transaction){ //Nothing is readable in here except intrinsic data types //This is the line, that when commented out, keeps the ability to display values working _groups.Load(details, type, startDate); } } _groups is a variable that references a custom class (that inherits directly from S) that has no "special" functionality in it whatsoever. Any suggestions or ideas? Thanks, Mike This list is hosted by DevelopMentor® http://www.develop.com View archives and manage your subscription(s) at http://discuss.develop.com

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# 2   June 21st, 2007, 07:30 AM

J. Merrill Guest   Posts: n/a   Time spent in forums: Reputation Power:

PRB: Cannot evaluate expression because a thread is stopped at a point where garbage collection is impossible... Well, the class referenced by _groups must have a method called Load. What's in it? Have you tried commenting out different lines in the Load method to see what no longer "keeps the ability to display values working"? At 04:33 PM 6/20/2007, Mike Andrews wrote (in part) private void Load(Guid guid, MarType type, DateTime startDate, >TransactionContext transaction){ //Nothing is readable in here except intrinsic data types //This is the line, that when commented out, keeps the ability to >display values working _groups.Load(details, type, startDate); } > >} > >_groups is a variable that references a custom class (that inherits directly >from S) that has no "special" functionality in it whatsoever. J. Merrill / Analytical Software Corp This list is hosted by DevelopMentor® http://www.develop.com View archives and manage your subscription(s) at http://discuss.develop.com

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# 3   June 21st, 2007, 12:01 PM

Mike Andrews Guest   Posts: n/a   Time spent in forums: Reputation Power:

PRB: Cannot evaluate expression because a thread is stopped at a point where garbage collection is impossible... I think I've discovered the issue and after talking with a Microsoft technical support rep. The rep didn't have an answer, but made a reference to the number of parameters which led me to look further. The issue seems to be the total size of all parameters passed in to the method. The "details" parameter in the _groups.Load() method is a struct. The struct itself is quite large in size with about 30 fields that contain DataTables, DataRelations and DataRows. When I converted the struct to a class, the problem disappeared. It seems to be that the struct cannot be passed byval like a class when the size of the struct is greater than some [unknown] value. A very weird problem indeed. Thanks, Mike 6/21/07, J. Merrill <jvm_cop (AT) spamcop (DOT) netwrote: > Well, the class referenced by _groups must have a method called Load. What's in it? Have you tried commenting out different lines in the Load method to see what no longer "keeps the ability to display values working"? > At 04:33 PM 6/20/2007, Mike Andrews wrote (in part) > private void Load(Guid guid, MarType type, DateTime startDate, >TransactionContext transaction){ //Nothing is readable in here except intrinsic data types //This is the line, that when commented out, keeps the ability to >display values working _groups.Load(details, type, startDate); } > >} > >_groups is a variable that references a custom class (that inherits directly >from S) that has no "special" functionality in it whatsoever. > J. Merrill / Analytical Software Corp > This list is hosted by DevelopMentor(r) http://www.develop.com > View archives and manage your subscription(s) at http://discuss.develop.com > This list is hosted by DevelopMentor® http://www.develop.com View archives and manage your subscription(s) at http://discuss.develop.com

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# 4   June 21st, 2007, 12:01 PM

Paul van Brenk Guest   Posts: n/a   Time spent in forums: Reputation Power:

PRB: Cannot evaluate expression because a thread is stopped at a point where garbage collection is impossible... Uh A struct is always passed by value (ie. Copied). A class is passed by reference (just the pointer) So yeah, I can imagine copying a struct with the size you describe could be a problem for the GC. Message From: Discussion of advanced .NET topics. [mailto:ADVANCED-DTNET (AT) DISCUSS (DOT) DEVELP.CM] Behalf Mike Andrews Sent: Thursday, June 21, 2007 17:47 To: ADVANCED-DTNET (AT) DISCUSS (DOT) DEVELP.CM Subject: Re: [ADVANCED-DTNET] PRB: Cannot evaluate expression because a thread is stopped at a point where garbage collection is impossible I think I've discovered the issue and after talking with a Microsoft technical support rep. The rep didn't have an answer, but made a reference to the number of parameters which led me to look further. The issue seems to be the total size of all parameters passed in to the method. The "details" parameter in the _groups.Load() method is a struct. The struct itself is quite large in size with about 30 fields that contain DataTables, DataRelations and DataRows. When I converted the struct to a class, the problem disappeared. It seems to be that the struct cannot be passed byval like a class when the size of the struct is greater than some [unknown] value. A very weird problem indeed. Thanks, Mike 6/21/07, J. Merrill <jvm_cop (AT) spamcop (DOT) netwrote: > Well, the class referenced by _groups must have a method called Load. What's in it? Have you tried commenting out different lines in the Load method to see what no longer "keeps the ability to display values working"? > At 04:33 PM 6/20/2007, Mike Andrews wrote (in part) > private void Load(Guid guid, MarType type, DateTime startDate, >TransactionContext transaction){ //Nothing is readable in here except intrinsic data types //This is the line, that when commented out, keeps the ability to >display values working _groups.Load(details, type, startDate); } > >} > >_groups is a variable that references a custom class (that inherits directly >from S) that has no "special" functionality in it whatsoever > J. Merrill / Analytical Software Corp > This list is hosted by DevelopMentor(r) http://www.develop.com > View archives and manage your subscription(s) at http://discuss.develop.com > This list is hosted by DevelopMentor(r) http://www.develop.com View archives and manage your subscription(s) at http://discuss.develop.com This list is hosted by DevelopMentor® http://www.develop.com View archives and manage your subscription(s) at http://discuss.develop.com

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# 5   June 21st, 2007, 12:01 PM

Mike Andrews Guest   Posts: n/a   Time spent in forums: Reputation Power:

PRB: Cannot evaluate expression because a thread is stopped at a point where garbage collection is impossible... Yes. And it makes sense now. I just wasn't thinking along those lines until the MS guy said something about it and I had time to think about it for a while. It's always something. LL. I didn't equate the GC having issues with debugger and the size of the struct. 6/21/07, Paul van Brenk <paul.van.brenk (AT) tamtam (DOT) nlwrote: > Uh A struct is always passed by value (ie. Copied). A class is passed by reference (just the pointer) So yeah, I can imagine copying a struct with the size you describe could be a problem for the GC. > Message From: Discussion of advanced .NET topics. [mailto: ADVANCED-DTNET (AT) DISCUSS (DOT) DEVELP.CM] Behalf Mike Andrews Sent: Thursday, June 21, 2007 17:47 To: ADVANCED-DTNET (AT) DISCUSS (DOT) DEVELP.CM Subject: Re: [ADVANCED-DTNET] PRB: Cannot evaluate expression because a thread is stopped at a point where garbage collection is impossible > I think I've discovered the issue and after talking with a Microsoft technical support rep. The rep didn't have an answer, but made a reference to the number of parameters which led me to look further. > The issue seems to be the total size of all parameters passed in to the method. The "details" parameter in the _groups.Load() method is a struct. The struct itself is quite large in size with about 30 fields that contain DataTables, DataRelations and DataRows. When I converted the struct to a class, the problem disappeared. It seems to be that the struct cannot be passed byval like a class when the size of the struct is greater than some [unknown] value. > A very weird problem indeed. > Thanks, Mike > > 6/21/07, J. Merrill <jvm_cop (AT) spamcop (DOT) netwrote: > Well, the class referenced by _groups must have a method called Load. What's in it? Have you tried commenting out different lines in the Load method to see what no longer "keeps the ability to display values working"? > At 04:33 PM 6/20/2007, Mike Andrews wrote (in part) > private void Load(Guid guid, MarType type, DateTime startDate, >TransactionContext transaction){ //Nothing is readable in here except intrinsic data types //This is the line, that when commented out, keeps the ability to >display values working _groups.Load(details, type, startDate); } > >} > >_groups is a variable that references a custom class (that inherits directly >from S) that has no "special" functionality in it whatsoever. > J. Merrill / Analytical Software Corp This list is hosted by DevelopMentor(r) http://www.develop.com > View archives and manage your subscription(s) at http://discuss.develop.com > This list is hosted by DevelopMentor(r) http://www.develop.com > View archives and manage your subscription(s) at http://discuss.develop.com > This list is hosted by DevelopMentor(r) http://www.develop.com > View archives and manage your subscription(s) at http://discuss.develop.com > This list is hosted by DevelopMentor® http://www.develop.com View archives and manage your subscription(s) at http://discuss.develop.com

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# 6   June 21st, 2007, 05:00 PM

Mike Andrews Guest   Posts: n/a   Time spent in forums: Reputation Power:

PRB: Cannot evaluate expression because a thread is stopped at a point where garbage collection is impossible... Does anyone know the maximum size of a struct that can be used in the Framework without having these issues? Thanks, Mike 6/21/07, Mike Andrews <outdoor.jellyroll (AT) gmail (DOT) comwrote: > Yes. And it makes sense now. I just wasn't thinking along those lines until the MS guy said something about it and I had time to think about it for a while. It's always something. LL. I didn't equate the GC having issues with debugger and the size of the struct. > 6/21/07, Paul van Brenk <paul.van.brenk (AT) tamtam (DOT) nlwrote: > Uh A struct is always passed by value (ie. Copied). A class is passed by reference (just the pointer) So yeah, I can imagine copying a struct with the size you describe could be a problem for the GC. > Message From: Discussion of advanced .NET topics. [mailto: ADVANCED-DTNET (AT) DISCUSS (DOT) DEVELP.CM] Behalf Mike Andrews Sent: Thursday, June 21, 2007 17:47 To: ADVANCED-DTNET (AT) DISCUSS (DOT) DEVELP.CM Subject: Re: [ADVANCED-DTNET] PRB: Cannot evaluate expression because a thread is stopped at a point where garbage collection is impossible > I think I've discovered the issue and after talking with a Microsoft technical support rep. The rep didn't have an answer, but made a reference to the number of parameters which led me to look further. > The issue seems to be the total size of all parameters passed in to the method. The "details" parameter in the _groups.Load() method is a struct. The struct itself is quite large in size with about 30 fields that contain DataTables, DataRelations and DataRows. When I converted the struct to a class, the problem disappeared. It seems to be that the struct cannot be passed byval like a class when the size of the struct is greater than some [unknown] value. > A very weird problem indeed. > Thanks, Mike > > 6/21/07, J. Merrill <jvm_cop (AT) spamcop (DOT) netwrote: > Well, the class referenced by _groups must have a method called Load. What's in it? Have you tried commenting out different lines in the Load method to see what no longer "keeps the ability to display values working"? > At 04:33 PM 6/20/2007, Mike Andrews wrote (in part) > private void Load(Guid guid, MarType type, DateTime startDate, >TransactionContext transaction){ //Nothing is readable in here except intrinsic data types //This is the line, that when commented out, keeps the ability to >display values working _groups.Load(details, type, startDate); } > >} > >_groups is a variable that references a custom class (that inherits directly >from S) that has no "special" functionality in it whatsoever. > J. Merrill / Analytical Software Corp > This list is hosted by DevelopMentor(r) http://www.develop.com > View archives and manage your subscription(s) at http://discuss.develop.com > This list is hosted by DevelopMentor(r) http://www.develop.com > View archives and manage your subscription(s) at http://discuss.develop.com > This list is hosted by DevelopMentor(r) http://www.develop.com > View archives and manage your subscription(s) at http://discuss.develop.com > This list is hosted by DevelopMentor® http://www.develop.com View archives and manage your subscription(s) at http://discuss.develop.com

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# 7   June 21st, 2007, 05:30 PM

Chris Anderson Guest   Posts: n/a   Time spent in forums: Reputation Power:

PRB: Cannot evaluate expression because a thread is stopped at a point where garbage collection is impossible... Does anyone know the maximum size of a struct that can be used in the Framework without having these issues? The general rule of thumb is : If you're worrying about the maximum size of a struct, it's already too big! Structs were designed to be used for small lightweight data types (like Point, Rectangle, etc) This list is hosted by DevelopMentor® http://www.develop.com View archives and manage your subscription(s) at http://discuss.develop.com

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# 8   June 21st, 2007, 06:00 PM

Mike Andrews Guest   Posts: n/a   Time spent in forums: Reputation Power:

PRB: Cannot evaluate expression because a thread is stopped at a point where garbage collection is impossible... Very true. I was just curious. I'm generally more sparing on my use of structs. Nevertheless, I still want to know the maximum size of a struct or if there is no size limit, the optimal size of a struct. 6/21/07, Chris Anderson <Chris (AT) activeide (DOT) comwrote: > Does anyone know the maximum size of a struct that can be used in the Framework without having these issues? > The general rule of thumb is : If you're worrying about the maximum size of a struct, it's already too big! > Structs were designed to be used for small lightweight data types (like Point, Rectangle, etc) > This list is hosted by DevelopMentor(r) http://www.develop.com > View archives and manage your subscription(s) at http://discuss.develop.com > This list is hosted by DevelopMentor® http://www.develop.com View archives and manage your subscription(s) at http://discuss.develop.com

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# 9   June 21st, 2007, 07:00 PM

Chris Anderson Guest   Posts: n/a   Time spent in forums: Reputation Power:

PRB: Cannot evaluate expression because a thread is stopped at a point where garbage collection is impossible... I've been trying to look for a cite, but can only tell you that I was told by a instructor (albeit a SQL Server 2005 one) anything bigger than about 150 bytes was too big (remembering that a reference to a DataTable, etc was only the size of the *reference* and not the size of the data table contents, etc), but really it depends on usage IM cite I *can* find is that "Unless you need reference type semantics, a class that is smaller than 16 bytes may be more efficiently handled by the system as a struct" (vs.71).aspx Not that that helps of course :-) Message From: Discussion of advanced .NET topics. [mailto:ADVANCED- DTNET (AT) DISCUSS (DOT) DEVELP.CM] Behalf Mike Andrews Sent: 22 June 2007 00:01 To: ADVANCED-DTNET (AT) DISCUSS (DOT) DEVELP.CM Subject: Re: [ADVANCED-DTNET] PRB: Cannot evaluate expression because a thread is stopped at a point where garbage collection is impossible Very true. I was just curious. I'm generally more sparing on my use of structs. Nevertheless, I still want to know the maximum size of a struct or if there is no size limit, the optimal size of a struct. 6/21/07, Chris Anderson <Chris (AT) activeide (DOT) comwrote: > Does anyone know the maximum size of a struct that can be used in the Framework without having these issues? > The general rule of thumb is : If you're worrying about the maximum size of a struct, it's already too big! > Structs were designed to be used for small lightweight data types (like Point, Rectangle, etc) > This list is hosted by DevelopMentor(r) http://www.develop.com > View archives and manage your subscription(s) at http://discuss.develop.com > This list is hosted by DevelopMentor(r) http://www.develop.com View archives and manage your subscription(s) at http://discuss.develop.com This list is hosted by DevelopMentor® http://www.develop.com View archives and manage your subscription(s) at http://discuss.develop.com

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# 10   June 25th, 2007, 08:30 AM

Mike Andrews Guest   Posts: n/a   Time spent in forums: Reputation Power:

PRB: Cannot evaluate expression because a thread is stopped at a point where garbage collection is impossible... Thank you Chris. I think the sum total sizes of the "references" for all the objects in the struct and the additional parameters on the method was greater than 256 bytes. I got word back from MS on this issue: "generally speaking, when the total size of the arguments passed to a callee function is larger than 256 bytes, JIT will make the caller function partially interruptible. In a partially interruptible code, not every location in the code is a GC safe point. Therefore, it might be unsafe to evaluate expression at certain locations. When this happens you get [the error message]." So it seems that even since the fields were references, the sum of all them exceeded the 256 byte *limit* for the debugger. 6/21/07, Chris Anderson <Chris (AT) activeide (DOT) comwrote: > I've been trying to look for a cite, but can only tell you that I was told by a instructor (albeit a SQL Server 2005 one) anything bigger than about 150 bytes was too big (remembering that a reference to a DataTable, etc was only the size of the *reference* and not the size of the data table contents, etc), but really it depends on usage IM > cite I *can* find is that "Unless you need reference type semantics, a class that is smaller than 16 bytes may be more efficiently handled by the system as a struct" > (vs.71).aspx > Not that that helps of course :-) > > > Message From: Discussion of advanced .NET topics. [mailto:ADVANCED- DTNET (AT) DISCUSS (DOT) DEVELP.CM] Behalf Mike Andrews Sent: 22 June 2007 00:01 To: ADVANCED-DTNET (AT) DISCUSS (DOT) DEVELP.CM Subject: Re: [ADVANCED-DTNET] PRB: Cannot evaluate expression because a thread is stopped at a point where garbage collection is impossible > Very true. I was just curious. I'm generally more sparing on my use of structs. > Nevertheless, I still want to know the maximum size of a struct or if there is no size limit, the optimal size of a struct. > > 6/21/07, Chris Anderson <Chris (AT) activeide (DOT) comwrote: > Does anyone know the maximum size of a struct that can be used in the Framework without having these issues? > The general rule of thumb is : If you're worrying about the maximum size of a struct, it's already too big! > Structs were designed to be used for small lightweight data types (like Point, Rectangle, etc) > This list is hosted by DevelopMentor(r) http://www.develop.com > View archives and manage your subscription(s) at http://discuss.develop.com > > This list is hosted by DevelopMentor(r) http://www.develop.com > View archives and manage your subscription(s) at http://discuss.develop.com > > This list is hosted by DevelopMentor(r) http://www.develop.com > View archives and manage your subscription(s) at http://discuss.develop.com > This list is hosted by DevelopMentor® http://www.develop.com View archives and manage your subscription(s) at http://discuss.develop.com

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