BorlandTalk.com Borland discussion newsgroups   Archives   FAQ   Search   Memberlist   Usergroups   Register   Profile   Log in to check your private messages   Log in  Using TClientSocket in multi-threaded app          BorlandTalk.com Forum Index -> C++ Builder (Internet Socket) View previous topic :: View next topic   Author Message Mark Atkin Guest Posted: Thu Apr 20, 2006 9:03 pm    Post subject: Using TClientSocket in multi-threaded app I have a multi-threaded application where each thread uses TClientSocket to communicate to a device on the network. I start a new thread for each device that I need to talk to. My main form starts each of these threads, and when a timer on the main form reaches 0, a flag is set in each thread to tell the thead that it is time to talk to it's device. The next time the thread checks it's status, the thread calls new TClientSocket to allocate a new socket connection to use for the communication, retrieves the data, then deletes it's instance of TClientSocket. Everything seems to work fine on my computer. When I tried it on a client's computer, I began getting AVs when the thread was calling new TClientSocket. I was creating my instances of TClientSocket as follows: TClientSocket *sock = new TClientSocket(MainForm); where MainForm is the address of my form with the timer and the form that creates the threads. My theory as to why I would get AVs is that maybe all three threads are calling new TClientSocket(MainForm) almost simultaneously and basically, some method and/or property from my MainForm is being accessed by all three threads to add the TClientSocket component to the ComponentList array and increment the ComponentCount for the MainForm. I changed the socket instantiation to new TClientSocket(NULL) and the problem has gone away. This seems to agree with my theory, but it's just a theory. The biggest hole in my theory that I can see is that it doesn't really explain why it would work on my PC and not my clients. We are both running XPSP2 on P4s. It still could be a timing issue, but I would like to prove this theory somehow. Also, the only advantage that I can see to having MainForm being the owner of the TClientSocket is that if something unexpected occurs and the TClientSocket doesn't get deleted somehow, the MainForm will free up the memory when the form gets destroyed. This advantage is greatly decreased by the fact that the form is never destroyed until the program exits, in which case Windows is going to free up the memory anyway. Any thoughts, opinions, or additional theories (or even proofs with examples ) on this would be greatly appreciated. Regards, Mark Atkin Back to top SF Guest Posted: Wed Apr 26, 2006 11:03 am    Post subject: Re: Using TClientSocket in multi-threaded app Quote: TClientSocket *sock = new TClientSocket(MainForm); I always use TClientSocket *sock = new TClientSocket(NULL); to create client sockets inside a thread. You yourself noticed this is the right way. Quote: My theory as to why I would get AVs is that maybe all three threads are calling new TClientSocket(MainForm) almost simultaneously and basically, I don't care about that. Why should MainForm be the owner of an object created inside a different thread? Quote: The biggest hole in my theory that I can see is that it doesn't really explain why it would work on my PC and not my clients. That should be deeply checked, but again, you shouldn't care too much IMO. Quote: It still could be a timing issue, Or another thousands of issues... Quote: Also, the only advantage that I can see to having MainForm being the owner of the TClientSocket is that if something unexpected occurs and the TClientSocket doesn't get deleted somehow, the MainForm will free up the memory when the form gets destroyed. Not a big advantage. Almost a disadvantage under certain points of view. Quote: This advantage is greatly decreased by the fact that the form is never destroyed until the program exits, in which case Windows is going to free up the memory anyway. Anyway, your thread should be strong enough to handle any possible problem and free the TClientSocket pointer by itself. Did you find anything more in the meantime? HTH, Stefano. Back to top Mark Atkin Guest Posted: Wed Apr 26, 2006 6:03 pm    Post subject: Re: Using TClientSocket in multi-threaded app "Remy Lebeau (TeamB)" <no.spam (AT) no (DOT) spam.com> wrote in message news:<444fab11$1 (AT) newsgroups (DOT) borland.com>... Quote: "Mark Atkin" <matkin (AT) windrock (DOT) com> wrote in message news:4447ee51$1 (AT) newsgroups (DOT) borland.com... The next time the thread checks it's status, the thread calls new TClientSocket to allocate a new socket connection to use for the communication, retrieves the data, then deletes it's instance of TClientSocket. A better approach would be to create the TClientSocket instance only once when the thread is created and then free the TClientSocket when the thread is being freed. You don't need to create a new TClientSocket instance over and over during the thread's lifetime. Just Connect/Disconnect it when needed. I have thought about doing this. I still might. Quote: When I tried it on a client's computer, I began getting AVs when the thread was calling new TClientSocket. That is because of the way you are managing the TClientSocket. Keep reading... I was creating my instances of TClientSocket as follows: TClientSocket *sock = new TClientSocket(MainForm); That is not thread-safe. You are telling the TClientSocket to be owned by a TForm that resides in another thread. All of the ownership management that the VCL does internally only works when used in a single thread. In this case, you should be using NULL instead to assign no owner to the TClientSocket at all. The thread manages the TClientSocket's lifetime, so there is no need to assign any owner anyway. I don't know much about the internals of the VCL, but that was the only conclusion I could come up with. I'm glad to know you came up with the same conclusion. Quote: My theory as to why I would get AVs is that maybe all three threads are calling new TClientSocket(MainForm) almost simultaneously and basically, some method and/or property from my MainForm is being accessed by all three threads to add the TClientSocket component to the ComponentList array and increment the ComponentCount for the MainForm. That is very likely, yes. Which is exactly why specifying an Owner is not thread-safe at all. Unfortunately for me, this is the first experience I've had with writing multi-threaded applications. It's definitely been a learning experience. Quote: I changed the socket instantiation to new TClientSocket(NULL) and the problem has gone away. There you go then. The biggest hole in my theory that I can see is that it doesn't really explain why it would work on my PC and not my clients. A fluke, nothing more. It is likely just a timing issue, which are very difficult to debug. Maybe your computer is slower then the client's computer and thus the problem doesn't show up as much on your machine since the main thread properties/members are not access quite as simultaneously. Everything always works fine on the development system, right? :P Quote: Also, the only advantage that I can see to having MainForm being the owner of the TClientSocket is that if something unexpected occurs and the TClientSocket doesn't get deleted somehow, the MainForm will free up the memory when the form gets destroyed. That is a very bad design when threads are involved. You should not be assigning ownership across threads. Each thread should own its own objects. If something goes bad and your main thread does not terminate the threads, the threads will still be running when the main thread frees the objects that the threads are using. Again, I'm learning more all the time about using threads. Quote: Gambit Thanks Gambit. Back to top Mark Atkin Guest Posted: Wed Apr 26, 2006 6:03 pm    Post subject: Re: Using TClientSocket in multi-threaded app "SF" <invalid (AT) NOSPAMinvalid (DOT) com> wrote in message news:<444f4499$2 (AT) newsgroups (DOT) borland.com>... Quote: TClientSocket *sock = new TClientSocket(MainForm); I always use TClientSocket *sock = new TClientSocket(NULL); Me too, from now on ;) Quote: to create client sockets inside a thread. You yourself noticed this is the right way. My theory as to why I would get AVs is that maybe all three threads are calling new TClientSocket(MainForm) almost simultaneously and basically, I don't care about that. Why should MainForm be the owner of an object created inside a different thread? When I first coded this, I didn't realize that NULL was a valid argument. I thought I had to supply a valid TComponent instance. I now know that's not the case. Quote: The biggest hole in my theory that I can see is that it doesn't really explain why it would work on my PC and not my clients. That should be deeply checked, but again, you shouldn't care too much IMO. I've got the same opinion, now. Who cares why it was working on my PC. It probably shouldn't have been. I guess I was lucky that it failed so quickly on my clients computer or this could have bitten me down the road. Quote: It still could be a timing issue, Or another thousands of issues... Also, the only advantage that I can see to having MainForm being the owner of the TClientSocket is that if something unexpected occurs and the TClientSocket doesn't get deleted somehow, the MainForm will free up the memory when the form gets destroyed. Not a big advantage. Almost a disadvantage under certain points of view. I see that, now. Quote: This advantage is greatly decreased by the fact that the form is never destroyed until the program exits, in which case Windows is going to free up the memory anyway. Anyway, your thread should be strong enough to handle any possible problem and free the TClientSocket pointer by itself. Did you find anything more in the meantime? Not really. This definitely seems to have fixed my problem. It wouldn't run more than 30 minutes before. Now, it has run for days with no problems. Quote: HTH, Stefano. Thanks Stefano. Back to top Remy Lebeau (TeamB) Guest Posted: Wed Apr 26, 2006 6:03 pm    Post subject: Re: Using TClientSocket in multi-threaded app "Mark Atkin" <matkin (AT) windrock (DOT) com> wrote in message news:4447ee51$1 (AT) newsgroups (DOT) borland.com... Quote: The next time the thread checks it's status, the thread calls new TClientSocket to allocate a new socket connection to use for the communication, retrieves the data, then deletes it's instance of TClientSocket. A better approach would be to create the TClientSocket instance only once when the thread is created and then free the TClientSocket when the thread is being freed. You don't need to create a new TClientSocket instance over and over during the thread's lifetime. Just Connect/Disconnect it when needed. Quote: When I tried it on a client's computer, I began getting AVs when the thread was calling new TClientSocket. That is because of the way you are managing the TClientSocket. Keep reading... Quote: I was creating my instances of TClientSocket as follows: TClientSocket *sock = new TClientSocket(MainForm); That is not thread-safe. You are telling the TClientSocket to be owned by a TForm that resides in another thread. All of the ownership management that the VCL does internally only works when used in a single thread. In this case, you should be using NULL instead to assign no owner to the TClientSocket at all. The thread manages the TClientSocket's lifetime, so there is no need to assign any owner anyway. Quote: My theory as to why I would get AVs is that maybe all three threads are calling new TClientSocket(MainForm) almost simultaneously and basically, some method and/or property from my MainForm is being accessed by all three threads to add the TClientSocket component to the ComponentList array and increment the ComponentCount for the MainForm. That is very likely, yes. Which is exactly why specifying an Owner is not thread-safe at all. Quote: I changed the socket instantiation to new TClientSocket(NULL) and the problem has gone away. There you go then. Quote: The biggest hole in my theory that I can see is that it doesn't really explain why it would work on my PC and not my clients. A fluke, nothing more. It is likely just a timing issue, which are very difficult to debug. Maybe your computer is slower then the client's computer and thus the problem doesn't show up as much on your machine since the main thread properties/members are not access quite as simultaneously. Quote: Also, the only advantage that I can see to having MainForm being the owner of the TClientSocket is that if something unexpected occurs and the TClientSocket doesn't get deleted somehow, the MainForm will free up the memory when the form gets destroyed. That is a very bad design when threads are involved. You should not be assigning ownership across threads. Each thread should own its own objects. If something goes bad and your main thread does not terminate the threads, the threads will still be running when the main thread frees the objects that the threads are using. Gambit Back to top Remy Lebeau (TeamB) Guest Posted: Wed Apr 26, 2006 10:03 pm    Post subject: Re: Using TClientSocket in multi-threaded app "Mark Atkin" <matkin (AT) windrock (DOT) com> wrote in message news:444faf4f$1 (AT) newsgroups (DOT) borland.com... Quote: I don't know much about the internals of the VCL, but that was the only conclusion I could come up with. I'm glad to know you came up with the same conclusion. I didn't "come up" with that conclusion. The behavior I described is a known fact. Besides, I have the VCL source code, so it is just a matter of looking up what the VCL actually does. Most of the VCL internals are NOT thread-safe, so you have to be VERY careful when using the VCL with threads. Gambit Back to top Display posts from previous: All Posts1 Day7 Days2 Weeks1 Month3 Months6 Months1 Year Oldest FirstNewest First         BorlandTalk.com Forum Index -> C++ Builder (Internet Socket) All times are GMT Page 1 of 1   Jump to: Select a forum C++ Builder Newsgroups----------------C++ BuilderC++ Builder (ActiveX)C++ Builder (Announcements)C++ Builder (Command Line Tools)C++ Builder DatabasesC++ Builder Databases (ADO)C++ Builder Databases (Desktop)C++ Builder Databases (InterBase Express)C++ Builder Databases (Multi-Tier)C++ Builder Databases (SQL Servers)C++ Builder (Graphics)C++ Builder (IDE)C++ Builder (Internet)C++ Builder (Internet Socket)C++ Builder (Internet Web)C++ Builder (Jobs)C++ Builder (Language)C++ Builder (Language C++)C++ Builder (Compatibility with MFC)C++ Builder (Native API)C++ Builder (Non-Technical)C++ Builder (Students)C++ Builder (Third Party Tools)C++ Builder (Upgrade)C++ Builder (VCL)C++ Builder (VCL Components Usage)C++ Builder (VCL Components Development)C++ Builder (VCL Usage)C++ Builder (WinAPI)C++ Builder Installation Delphi Newsgroups----------------Delphi (General)Delphi ActiveX Controls UsageDelphi ActiveX Controls DevelopmentDelphi As400Delphi DatabasesDelphi Databases (ADO)Delphi Databases (dbExpress)Delphi Databases (Desktop)Delphi Databases (InterBase Express)Delphi Databases (Multi-Tier)Delphi Databases (SQL Servers)Delphi DeploymentDelphi GraphicsDelphi IDEDelphi InternationalizationDelphi InternetDelphi Internet Isapi-WebBrokerDelphi Internet WebSnapDelphi Internet WinsockDelphi JobsDelphi Language BASMDelphi Language ObjectPascalDelphi Model Driven Architecture (General)Delphi Model Driven Architecture (Third Party)Delphi MultimediaDelphi Native APIDelphi Non-TechnicalDelphi ObjectPascalDelphi OLE AutomationDelphi OO designDelphi OpenToolsAPIDelphi Reporting-ChartingDelphi RTLDelphi StudentsDelphi TeamSourceDelphi Thirdparty ToolsDelphi Thirdparty Tools (General)Delphi Thirdparty Tools (IntraWeb)Delphi Thirdparty Tools (RaveReports)Delphi UpgradeDelphi VCLDelphi VCL ComponentsDelphi VCL Components UsingDelphi VCL Components WritingDelphi WebServices SOAPDelphi WinAPIDelphi XMLDelphi Installationcomp.lang.pascal.delphi.components.misccomp.lang.pascal.delphi.components.usagecomp.lang.pascal.delphi.components.writingcomp.lang.pascal.delphi.databasescomp.lang.pascal.delphi.misccomp.sources.delphi JBuilder Newsgroups----------------JBuilderJBuilder AnnouncementsJBuilder Applet IssuesJBuilder As400JBuilder CompilerJBuilder CORBA/RMIJBuilder DatabasesJBuilder DB SwingJBuilder DebuggerJBuilder DeploymentJBuilder DocumentationJBuilder EnterpriseJBuilder HandheldJBuilder IDEJBuilder JavaJBuilder JavaAPIJBuilder Java LanguageJBuilder Java SwingJBuilder Java BeansJBuilder Java Beans UsageJBuilder Java Beans DevelopmentJBuilder JBCLJBuilder JDataStoreJBuilder JobsJBuilder LinuxJBuilder MacintoshJBuilder & MobileSetJBuilder MultiLingual AppsJBuilder Non-TechnicalJBuilder OpenToolsJBuilder Servlets (JSP)JBuilder StudentsJBuilder Team DevelopmentJBuilder Thirdparty ToolsJBuilder UpgradeJBuilder Installation InterBase Newsgroups----------------InterBaseInterBase Bug DiscussionInterBase GeneralInterBase IBConsoleInterBase OpenSourceInterBase ReplicationInterBase SQLInterBase ThirdpartyInterBase Installation Miscellaneous Borland Newsgroups----------------AppCenterAppServerEnteraVisiBroker  You cannot post new topics in this forum You cannot reply to topics in this forum You cannot edit your posts in this forum You cannot delete your posts in this forum You cannot vote in polls in this forum Powered by phpBB © 2001, 2006 phpBB Group SEO toolkit © 2004-2006 webmedic.