Monday, April 13, 2009

callback (listener,functor,event handler,observer)@what thread@@

Whenever I see a callback, listener, observer or event handler [1], i ask
Q1: In which thread does the callback run?
Q2: In which thread does the caller run? Note caller method might spawn a new thread to run the callback.
Q3: In which thread does the event generator/sender run? Usually not the same as the callback method.
Q4: is there a network daemon running a blocking accept()? I feel this is a fundamental question. In Swing and Case 3 below, there's no network daemon so event generator can invoke the callback in the same thread.

Case 1: swing -- experiments show the callback runs in the event-queue thread i.e. EDT. If you suspend the event-queue thread, you see the thread waits in wait()

Case 2: onMessage
Case 3: spring jdbc template
case 4: servlet event listeners
case 5: java.util.Observer. I think the detailed chapter in [[head first design patterns]] is a single-threaded example. The update operation triggers all the callbacks in a single thread.

I guess in both Swing and Rendezvous, listeners are in a static collection. GC can't reclaim them. Memory leak!

http://www.java-tips.org/java-se-tips/java.util/using-weakhashmap-for-listener-lists.html says listeners are strong references and are not garbage collected, so we must remember to remove the listener. Also see http://www.javalobby.org/java/forums/t19468.html

Doug Lea has a chapter on callbacks in a threaded environment.

A worthwhile distinction -- Note a "listener" (and sometimes a callback) is an object; a "callback" is often a dynamic method CALL, or you can think of it as a METHOD in source code, loaded into JVM as part of the class object. Now at registration time, the listener's object reference (ie memory address) is submitted, photo-copied and stored in the registry.

[1] a method, object, nested class..

No comments:

Total Pageviews

my favorite topics (labels)

_fuxi (302) _misLabel (13) _orig? (3) _rm (2) _vague (2) clarified (58) cpp (39) cpp_const (22) cpp_real (76) cpp/java/c# (101) cppBig4 (54) cppSmartPtr (35) cppSTL (33) cppSTL_itr (27) cppSTL_real (26) cppTemplate (28) creditMkt (14) db (65) db_sybase (43) deepUnder (31) dotnet (20) ECN (27) econ/bank` (36) fin/sys_misc (43) finGreek (34) finReal (45) finRisk (30) finTechDesign (46) finTechMisc (32) finVol (66) FixedIncom (28) fMath (7) fMathOption (33) fMathStoch (67) forex (39) gr8IV_Q (46) GTD_skill (15) GUI_event (30) inMemDB (42) intuit_math (41) intuitFinance (57) javaMisc (68) javaServerSide (13) lambda/delegate (22) marketData (28) math (10) mathStat (55) memIssue (8) memMgmt (66) metaProgram` (6) OO_Design (84) original_content (749) polymorphic/vptr (40) productive (21) ptr/ref (48) py (28) reflect (8) script`/unix (82) socket/stream (39) subquery/join (30) subvert (13) swing/wpf (9) sysProgram` (16) thread (164) thread_CAS (15) thread_cpp (28) Thread* (22) timeSaver (80) transactional (23) tune (24) tuneDB (40) tuneLatency (30) z_ajax (9) z_algoDataStruct (41) z_arch (26) z_arch_job (27) z_automateTest (17) z_autoTrad` (19) z_bestPractice (39) z_bold (83) z_bondMath (35) z_book (18) z_boost (19) z_byRef^Val (32) z_c#GUI (43) z_c#misc (80) z_cast/convert (28) z_container (67) z_cStr/arr (39) z_Favorite* (8) z_FIX (15) z_forex (48) z_fwd_Deal (18) z_gz=job (33) z_gzBig20 (13) z_gzMgr (13) z_gzPain (20) z_gzThreat (19) z_hib (19) z_IDE (52) z_ikm (5) z_IR_misc (36) z_IRS (26) z_javaWeb (28) z_jdbc (10) z_jobFinTech (46) z_jobHunt (20) z_jobRealXp (10) z_jobStrength (15) z_jobUS^asia (27) z_letter (42) z_linq (10) z_memberHid` (11) z_MOM (54) z_nestedClass (5) z_oq (24) z_PCP (12) z_pearl (1) z_php (20) z_prodSupport (7) z_py (31) z_quant (14) z_regex (8) z_rv (38) z_skillist (48) z_slic`Problem (6) z_SOA (14) z_spring (25) z_src_code (8) z_swingMisc (50) z_swingTable (26) z_unpublish (2) z_VBA/Excel (8) z_windoz (17) z_wpfCommand (9)

About Me

New York (Time Square), NY, United States
http://www.linkedin.com/in/tanbin