Wednesday, October 19, 2011

pbref^pbclone in c#, c++ and java, again

Let's Assume a 32-bit machine.

- java primitive param in a method? Value (up to 64bit) is copied -- to the call stack
- java reference param? the 32-bit virtual address of the heapy thingy is copied. Note the caller must provide a tuple consisting of
*** a heapy thingy
*** a 32-bit address, possibly anonymous (How? [1])

C++ by-reference param? the 32-bit address is copied into the function's stack frame
C++ non-reference param? entire chunk of memory of the argument object is copied, from stack/heap[2] to stack
C++ pointer param? Reference to pointer is illegal.  Declaration is f(someType *). Caller must plug in a 32-bit address of a someType instance. The 32-bit pointer is copied.
C++ double-pointer param? Declaration is f(someType **). See http://bigblog.tanbin.com/2011/04/double-pointer-usage-2-special.html
Note C++ has no rule differentiating a basic type (like char/float) vs a user-defined class.

C# is more complicated
c# by-value on simple/struct type? Entire chunk of memory is copied into the method stack frame
c# by-value on reference-type? 32-bit address copied, just like java reference param
c# ref-param on reference-type? See diagram on P71 [[C#Precisely]] (Value type easier)
** this is true call-by-reference, unsupported in Java
** like C++ double pointer param
** The caller must provide a 32-bit address of a reference variable [3] myvar. Literals like 123 is not a variable therefore unacceptable. Since myvar is a 32-bit pointer, it may point to a 32-bit address 0xAA112233 on heap OR stack
** Let's say myvar itself has address 0xFFEEFF12. This address is copied into the method as parameter myParam
** myParam becomes a permanent __alias__ of myvar. Effectively 2 names at the same address. myParam may not get a 32-bit storage but it doesn't matter.
** in the method, assignment to myParam _reseats_ myvar, to 0xAA110000 for example.
** after the method, myvar still points to 0xAA110000

Note when a 32-bit address is copied (pbref), then any change to the pointee is visible after the call; invisible for pbclone.

Note in general, pointee can be on stack or heap

[1] if you pass in new MyType()
[2] how would a nonref param passing involve copying from heap? Granted parameter is nonref, but the argument could be an unwrapped pointer. Another case -- a heap object's field is passed into the function.
[3] myvar can be a primitive variable. Look at P71 [[c#precisely]] to see the difference.

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