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.NET Forum / Windows Forms / WinForm General / March 2006Fast Searches of a Thread Safe Collection of Structs
In a Windows Forms application I plan to have a collection of structs - each of which contains a bunch of properties describing a person (e.g., LastName, FirstName, EmployeeID, HomeAddress, ZipCode, etc). So each instance of the struct will describe a person - and about 900 instances (people) will be contained in the collection. Users must be able to search for a specific person by any of the properties (e.g., LastName, FirstName, EmployeeID, HomeAddress, ZipCode, etc). So the collection must be searchable by all of the properties of the contained struct instances. Please note that the comparison will be between (1) a string the user is typing into a textbox, and (2) the specified property (e.g., LastName) -- such that AS the user types, a list displayed elsewhere on the form will dynamically show ALL of the closest matches (closest to the string the user is typing AS the user types). The collection will periodically be updated on a background thread (every 15 or so minutes) - so the collection must be "thread safe." MY QUESTIONS: 1. How do I make the collection of structs searchable by *each* of its properties (LastName, FirstName, Zip, etc...). Of course only one property at a time would be searched on. I would think implementing IComparable would work - but apparently doing so would let me enable searching on only one of the properties (but I need to enable searching on ALL of the properties). 2. How do I make the collection "thread safe" so that the collection can be updated by a background thread while users may be searching for a person in the collection. Note: people [in the collection] will almost never be deleted - so phantom matches are not really a concern. Just looking for high-level direction on this. Thank you very much! Lock the list during reads and writes. Use List<struct> and Find() using different Predicate delegates for your different search needs.  SignatureWilliam Stacey [MVP] | In a Windows Forms application I plan to have a collection of structs - each | of which contains a bunch of properties describing a person (e.g., LastName, [quoted text clipped - 31 lines] | | Thank you very much! And you almost certainly shouldn't be using use structs for a Person class. Your post talks about the string that the person is "typing" into a box - this sounds like an incremental search to me - if so you would need to sort the list for the particular property instead of using predicates. > Lock the list during reads and writes. Use List<struct> and Find() using > different Predicate delegates for your different search needs. [quoted text clipped - 49 lines] > | > | Thank you very much! Thanks William... can you expand just a bit? I'm not clear on [... Predicate delegates... ]. -Jeff > Lock the list during reads and writes. Use List<struct> and Find() using > different Predicate delegates for your different search needs. [quoted text clipped - 49 lines] > | > | Thank you very much! > Thanks William... can you expand just a bit? I'm not clear on [... Predicate > delegates... ]. Just to check before too much detail is gone into - are you using .NET 2.0 or 1.1? You won't be able to use List<T> if you're only using 1.1. Also, do you *have* to use structs? Why are you using structs rather than classes? SignatureJon Skeet - <skeet@pobox.com> http://www.pobox.com/~skeet Blog: http://www.msmvps.com/jon.skeet If replying to the group, please do not mail me too RE: << are you using 2.0 or 1.1?>> I could develop in either. Preference is for 2.0 although preliminary work has been done in 1.1 (I'll be migrating soon and this particular issue may cause me to go to 2.0 immediately)... This also means I haven't used generics yet and I haven't done any non trivial work yet in 2.0. RE: <<do you *have* to use structs? Why are you using structs rather than classes?>> I was using structs simply because they are lighter weight than classes. All I really need here is "a bunch of properties that identify a person" and my thinking was that a struct would be sufficient. That's all. I could just as easily implement with classes or ?? (this thing is still in the design phase and I haven't written much code for it yet. Thanks! >> Thanks William... can you expand just a bit? I'm not clear on [... >> Predicate [quoted text clipped - 5 lines] > Also, do you *have* to use structs? Why are you using structs rather > than classes? > RE: > << are you using 2.0 or 1.1?>> > I could develop in either. Preference is for 2.0 although preliminary work > has been done in 1.1 (I'll be migrating soon and this particular issue may > cause me to go to 2.0 immediately)... This also means I haven't used > generics yet and I haven't done any non trivial work yet in 2.0. Using generics in .NET 2.0 would mean you could avoid boxing performance overheads using generic collections, if you do end up using a value type. > RE: > <<do you *have* to use structs? Why are you using structs rather than > classes?>> > I was using structs simply because they are lighter weight than classes. Actually, they're often heavier. Any time you're passing round a struct which has more than a few properties, that's going to heavier than using a class. Value types can often be harder to work with, too. > All I really need here is "a bunch of properties that identify a > person" and my thinking was that a struct would be sufficient. That's > all. I could just as easily implement with classes or ?? (this thing > is still in the design phase and I haven't written much code for it > yet. I *strongly* suggest that you learn more about .NET and C# before going any further. A decent understanding of the difference between value types and reference types is absolutely crucial to programming in .NET, for a start. SignatureJon Skeet - <skeet@pobox.com> http://www.pobox.com/~skeet Blog: http://www.msmvps.com/jon.skeet If replying to the group, please do not mail me too RE: << I *strongly* suggest that you learn more about .NET and C# before going any further>> I *certainly* agree with you that I should learn more about .NET - but your recommendation is so vague as to be not helpful. My OP was specifically NOT asking for code samples or otherwise for others to do my work BECAUSE I was wanting high-level guidance that would help me to focus my learning in a way that is relevant to the current project. That's how a lot of learning happens - I'm sure you've likely done the same many times over your career. The response by William Stacey was pretty much the sort of guidance I was looking for - but I was just wanting a little bit more, like what a Predicate delegate is. Before I asked him to clarify I googled it and found nothing apparently relevant... then went to my 3.0 books and didn't find anything helpful... thus my followup post. I know what a delegates is - just not sure of the "Predicate" delegate part of his recommendation. I hope that doesn't make me too dumb to be helped. -Jeff >> RE: >> << are you using 2.0 or 1.1?>> [quoted text clipped - 28 lines] > types and reference types is absolutely crucial to programming in .NET, > for a start. > << I *strongly* suggest that you learn more about .NET and C# before going > any further>> > I *certainly* agree with you that I should learn more about .NET - but your > recommendation is so vague as to be not helpful. Okay, here's a more concrete recommendation: read a book or tutorial about C# and .NET which starts from a beginner's perspective. Pay close attention to chapters which describe the differences between value types and reference types, and parameter passing, too. > My OP was specifically NOT > asking for code samples or otherwise for others to do my work BECAUSE I was > wanting high-level guidance that would help me to focus my learning in a way > that is relevant to the current project. That's how a lot of learning > happens - I'm sure you've likely done the same many times over your career. Well, I usually haven't tried to embark on a real-life project without a reasonable understanding of the basics of what I'm using. It's fine to use projects to learn, but I wouldn't try it with a real world production project, which I assumed your question was about (given the very specific nature of it). Threading is a relatively advanced topic, for instance - so one would hope that someone asking a question involving threading (as yours did) would have a good grounding in the basics. > The response by William Stacey was pretty much the sort of guidance I was > looking for - but I was just wanting a little bit more, like what a [quoted text clipped - 3 lines] > not sure of the "Predicate" delegate part of his recommendation. I hope that > doesn't make me too dumb to be helped. You're not too dumb to be helped at all - but without a good understanding of the fundamentals of the framework, I don't think it's a good idea to continue with a real project. Put it this way - asking about delegates without understanding value types is a bit like someone asking for good examples of the subjunctive mood without understanding the difference between a verb and a noun. I *could* give you examples of implementing predicates using anonymous methods etc, but the chances of you properly understanding those examples without a sound knowledge of the basics are very slim. In short, I don't think it would be helpful in the long run. SignatureJon Skeet - <skeet@pobox.com> http://www.pobox.com/~skeet Blog: http://www.msmvps.com/jon.skeet If replying to the group, please do not mail me too I agree with Jon for this reason - if you get an example of how to do the sort you will be doing ONE thing right (and even then you could have done it the hard way - it would just be slower) but if you if you continue to misunderstand when it is appropriate to use a struct you will be doing MANY things wrong and they will manifest themselves throughout your as they will be used in multiple places whereas the sorting is only done in a single method. Careful on the attitude.. the line between berating and mentoring might seem fine, but it never is to the recipient of either. While I agree with your sentiments, I think as an MVP you might do a better job at encouragement. Perhaps spend a little more time explaining, otherwise, perhaps not say anything at all. > Careful on the attitude.. the line between berating and mentoring might > seem fine, but it never is to the recipient of either. While I agree > with your sentiments, I think as an MVP you might do a better job at > encouragement. Perhaps spend a little more time explaining, otherwise, > perhaps not say anything at all. If the OP shows some interest in really learning the differences between value types and reference types, I'll be very happy to help. However, I believe that explaining something advanced when we *know* the basics are missing is a bad idea - in my experience it only leads to more questions which could easily be avoided by learning those basics first. I've seen it time and time again in newsgroups (it was worse on the Java ones). I dare say I could have expressed it better though... SignatureJon Skeet - <skeet@pobox.com> http://www.pobox.com/~skeet Blog: http://www.msmvps.com/jon.skeet If replying to the group, please do not mail me too Do you have the MSDN help installed? Look in the List<T>.Find method help. What version of VS are you using? SignatureWilliam Stacey [MVP] > I was using structs simply because they are lighter weight than classes. I will add my voice to the chorus: use classes not structs in this case. There are occasions when it is appropriate to use structs instead of classes "...because they are lighter weight..." but these occasions are very, very rare indeed. The perception that structs are nothing more than "classes lite" is just dead wrong. Fortunately, most new programmers who insist on forging ahead with structs find this out "the hard way." Unfortunately some of them then conclude that C# is junk, rather than realizing that failing at pounding in a nail with a screwdriver does not mean that screwdrivers are useless. > Users must be able to search for a specific person by any of the properties (e.g., LastName, FirstName, EmployeeID, HomeAddress, ZipCode, etc). I would approach this as follows. Check into the Comparer class and the IComparer interface that it implements. These would allow you to write generic searching code that takes a Comparer and a Person as its arguments and finds the Person or Persons from the list that "compare equal" to the given Person based on the results of your particular Comparer. This also allows you to search based on any combination of the given properties in one simple operation, simply by varying the Comparer. You could also build more sophisticated Comparers that allow for wildcard searches, "LIKE" searches, and other things like that. Whatever you eventually decide to do, make Person a class. If you want to know exactly why, try searching this newsgroup for "struct vs class" or words to that effect. The topic comes up often here, frequently raised by frustrated programmers who don't understand why C# is acting so weird. :) Just a quick thought, but have you looked at the ADO classes for performance, vs. a struct that implement IComparable? With what you are describing as a disconnected data source, the filter expressions should make the overall task easier, but I don't know what if any implications it would have as far as thread locking is concerned. I have been impressed with ADO.NET's performance in scenarios like this. Worth checking I supposed. Let us know what you find. Regards John Parrish
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