iphone - Objective-C multithreading, what happens when an object gets dealloc while its methods are being executed? (And how to prevent it?) -

-

i writing app iphone , arrived @ situation.

i have view controller, myviewcontroller, dealloc whenever user taps "back" button on screen. there thread in background communicates remote server , may message method, updateui, method in myviewcontroller.

what happen if background thread messages updateui in myviewcontroller, user happened tapped "back" button @ right time such causes myviewcontroller dealloc while updateui still executing?

my guess dealloc method run , app might crash if updateui ends using null pointer. assuming case, current solution have is:

[self retain]; // updateui code here [self release];

i unsure if best solution, feel common problem when dealing multiple threads.

is assumption correct? if so, there better solution?

what describing known "race condition." race conditions can difficult identify in testing, track down once reported, , reproduce because execution in debugger can modify how code being executed (avoiding condition 1 trying reproduce). race conditions 1 of major pitfalls in concurrent programming - making area deceptively difficult well.

in principle, best practice minimize use of shared resources , closely qualify how sharing coordinated when implementing concurrency. if object shared across multiple threads, should retained each of them ensure object stays in-scope while each thread completes processing.

apple has been taking steps simplify implementing concurrency. starting point familiarizing topic on ios. http://developer.apple.com/library/ios/#documentation/general/conceptual/concurrencyprogrammingguide/introduction/introduction.html%23//apple_ref/doc/uid/tp40008091

it's useful aware objective-c 2.0's properties can support atomic operations (and atomic default, nonatomic keyword disable default). http://developer.apple.com/library/mac/#documentation/cocoa/conceptual/objectivec/articles/ocproperties.html

and, old-school guide threads (out of favor approach, still useful background - sure familiar nslock). http://developer.apple.com/library/mac/#documentation/cocoa/conceptual/multithreading/introduction/introduction.html%23//apple_ref/doc/uid/10000057i


Comments

Post a Comment

Popular posts from this blog

java - SNMP4J General Variable Binding Error -

-
i trying use snmp4j snmp bulkget. when ever use snmp4j make call returned responseevent error says "general variable binding error" , data returned equal null. to debug: print out, console, exact oid , version number using in snmp4j. use printed out data snmpwalk on command line. valid results. know sending snmp4j correct pdu correct oid, version number, max repititions, etc. i have used snmp4j , code wrote succesffuly monitor other devices years. don't know different time. leaving me stumped. why "general variable binding error?" causes error? ideas debug? can reproduced? if so, first action should using wireshark or microsoft network monitor capture network packets. my guess agent gives generr response, not surprising, http://www.ietf.org/rfc/rfc1157.txt
Read more

windows - Python Service Installation - "Could not find PythonClass entry" -

-
i working on building python service. inducing error, not sure inducing it. ps c:\...> python .\file.py debug debugging service myservice - press ctrl+c stop. error 0xc00000f4 - not find service's pythonclass entry in registry error 1814 - specified resource name cannot found in image file. error 0xc0000080 - not locate module name in python class string (ie, no '.') this error coming pythonservicemessages.mc in pythonwin32. it turns out error result caused exception being thrown , python script dying off.
Read more

Determine if a XmlNode is empty or null in C#? -

-
the following code takes xmlnode data type , populates dataset object xmlnode content. write dataset's content file. public void populatedataset(xmlnode node) { xmlnodereader reader = new xmlnodereader(node); dataset ds = new dataset(); ds.readxml(reader); system.guid guid = system.guid.newguid(); string name = string.format("{0}{1}_{2}.xml", utility.xmloutputpath, utility.xmloutputfilename, guid.tostring()); //need write "node empty" file if xmlnode object empty of null ds.writexml(name, xmlwritemode.ignoreschema); } the problem encountered 1 scenario not write content file. how determine if xmlnode object null or empty? you can check if node parameter null or has innertext or innerxml properties null or empty, when enter method before creating xmlnodereader .
Read more