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Background delegates
gitbaum edited this page Jul 29, 2011
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Delegates are a concept from C# for storing member function pointers (and ordinary function pointers, and static member function pointers, ...), but thereby avoiding virtual functions. More info is available at:
- Delegates in C#: http://www.codeproject.com/KB/cs/delegates.aspx
- Very short overview covering different approaches in C++: http://www.rsdn.ru/Forum/Message.aspx?mid=1712875&only=1
- A general explanation: http://aigamedev.com/programming-tips/fast-delegates-game-logic
- Sergey Ryazanov: http://www.codeproject.com/KB/cpp/ImpossiblyFastCppDelegate.aspx
- myelin: http://www.myelin.co.nz/notes/callbacks/cpp-delegates.html
- Yet Another Generalized Functors Implementation in C++: http://www.codeproject.com/KB/cpp/genfunctors.aspx
- Don Clugston: http://www.codeproject.com/KB/cpp/FastDelegate.aspx
- JaeWook Choi, Delegates with Boost: http://www.codeproject.com/KB/cpp/fastdelegate2.aspx
- Callbacks in C++ using template functors, "origin" of delegates, from 1994: http://www.tutok.sk/fastgl/callback.html
Example:
static void scw_notify_receivers( struct netpacket_handler_args* args )
{
receivers[3]( 0x1a, 0x2b, 0 );
}
Assembler output:
00002bf6 <_ZN7wiselib20scw_notify_receiversEP22netpacket_handler_args>: 2bf6: 0c 43 clr r12 ; 2bf8: 7d 40 2b 00 mov.b #43, r13 ;#0x002b 2bfc: 3e 40 1a 00 mov #26, r14 ;#0x001a 2c00: 1f 42 80 11 mov &0x1180,r15 ;0x1180 2c04: 92 12 82 11 call &0x1182 ; 2c08: 30 41 ret
Assembler output:
00002c22 <_ZN7wiselib20scw_notify_receiversEP22netpacket_handler_args>: 2c22: 0b 12 push r11 ; 2c24: 0a 12 push r10 ; 2c26: 1d 42 88 11 mov &0x1188,r13 ;0x1188 2c2a: 1e 42 8a 11 mov &0x118a,r14 ;0x118a 2c2e: 1a 42 86 11 mov &0x1186,r10 ;0x1186 2c32: 0a 5e add r14, r10 ; 2c34: 0f 4d mov r13, r15 ; 2c36: 1f f3 and #1, r15 ;r3 As==01 2c38: 4f 93 cmp.b #0, r15 ;r3 As==00 2c3a: 05 24 jz $+12 ;abs 0x2c46 2c3c: 0f 4d mov r13, r15 ; 2c3e: 1f c3 bic #1, r15 ;r3 As==01 2c40: 2f 5a add @r10, r15 ; 2c42: 2b 4f mov @r15, r11 ; 2c44: 01 3c jmp $+4 ;abs 0x2c48 2c46: 0b 4d mov r13, r11 ; 2c48: 0c 43 clr r12 ; 2c4a: 7d 40 2b 00 mov.b #43, r13 ;#0x002b 2c4e: 3e 40 1a 00 mov #26, r14 ;#0x001a 2c52: 0f 4a mov r10, r15 ; 2c54: 8b 12 call r11 ; 2c56: 3a 41 pop r10 ; 2c58: 3b 41 pop r11 ; 2c5a: 30 41 ret
Example:
virtual void execute( void *data )
{
del_( data );
//del_ = isense_timer_delegate_t();
}
Assembler output:
04001ee4 <__ZNK9delegate1IvPvEclES0_>: 4001ee4: 9c 21 ff fc b.addi r1,r1,-0x4 4001ee8: d4 01 48 00 b.sw 0x0(r1),r9 4001eec: 84 e3 00 04 b.lwz r7,0x4(r3) 4001ef0: 48 00 38 00 l.jalr r7 4001ef4: 84 63 00 00 b.lwz r3,0x0(r3) 4001ef8: 85 21 00 00 b.lwz r9,0x0(r1) 4001efc: 44 00 48 00 l.jr r9 4001f00: 9c 21 00 04 b.addi r1,r1,0x4 04001f04 <__ZN7wiselib74_GLOBAL__N_.._.._external_interface_isense_isense_os.cpp_00000000_6B6A63C719iSenseTimerCallback7executeEPv>: 4001f04: 03 ff ff f8 l.j 4001ee4 <__ZNK9delegate1IvPvEclES0_> 4001f08: 9c 63 00 04 b.addi r3,r3,0x4
Assembler output:
04001f44 <__ZNK12fastdelegate13FastDelegate1IPvvEclES1_>: 4001f44: 9c 21 ff e4 b.addi r1,r1,-0x1c 4001f48: d4 01 48 18 b.sw 0x18(r1),r9 4001f4c: d4 01 c0 14 b.sw 0x14(r1),r24 4001f50: d4 01 d0 10 b.sw 0x10(r1),r26 4001f54: ab 44 00 00 b.ori r26,r4,0x0 4001f58: 07 ff ff f6 l.jal 4001f30 <__ZNK12fastdelegate6detail10ClosurePtrIMNS0_12GenericClassEFvPvEPFvS3_ES7_E16GetClosureMemPtrEv> 4001f5c: 87 03 00 00 b.lwz r24,0x0(r3) 4001f60: d4 01 58 00 b.sw 0x0(r1),r11 4001f64: d4 01 60 04 b.sw 0x4(r1),r12 4001f68: d4 01 58 08 b.sw 0x8(r1),r11 4001f6c: a4 eb 00 01 b.andi r7,r11,0x1 4001f70: bc 07 00 00 b.sfeqi r7,0x0 4001f74: 10 00 00 06 b.bf 4001f8c <__ZNK12fastdelegate13FastDelegate1IPvvEclES1_+0x48> 4001f78: d4 01 60 0c b.sw 0xc(r1),r12 4001f7c: e0 f8 60 00 b.add r7,r24,r12 4001f80: 84 e7 00 00 b.lwz r7,0x0(r7) 4001f84: e0 e7 58 00 b.add r7,r7,r11 4001f88: 85 67 ff ff b.lwz r11,-0x1(r7) 4001f8c: e0 78 60 00 b.add r3,r24,r12 4001f90: 48 00 58 00 l.jalr r11 4001f94: a8 9a 00 00 b.ori r4,r26,0x0 4001f98: 87 41 00 10 b.lwz r26,0x10(r1) 4001f9c: 87 01 00 14 b.lwz r24,0x14(r1) 4001fa0: 85 21 00 18 b.lwz r9,0x18(r1) 4001fa4: 44 00 48 00 l.jr r9 4001fa8: 9c 21 00 1c b.addi r1,r1,0x1c 04001fac <__ZN7wiselib74_GLOBAL__N_.._.._external_interface_isense_isense_os.cpp_00000000_1DE8CCC319iSenseTimerCallback7executeEPv>: 4001fac: 03 ff ff e6 l.j 4001f44 <__ZNK12fastdelegate13FastDelegate1IPvvEclES1_> 4001fb0: 9c 63 00 04 b.addi r3,r3,0x4