Data Exchange between Applications

Q. Are there methods of organizing information exchange between running applications?

I have already described various methods of synchronization and using the shared memory. There is another interesting approach implemented in Windows anonymous (unnamed) pipes. ^[i] This approach is the most efficient for organizing information exchange with the console process generated by the current process. Assume that you need your console process started by some application (e.g., some string compiler) to output information to the edit window of the primary process instead of to console. The example of such application is shown in Listing 18.3.

Listing 18.3: Communications with console process through an anonymous pipe

 // The PIPE.RC file // Constant definitions #define WS_SYSMENU   0x00080000L #define WS_VISIBLE   0x100000000L #define WS_TABSTOP   0x00010000L #define WS_VSCROLL   0x00200000L #define DS_3DLOOK    0x0004L #define ES_LEFT      0x0000L #define WS_CHILD     0x40000000L #define WS_BORDER    0x00800000L #define ES_MULTILINE 0x0004L #define WS_VSCROLL   0x00200000L #define WS_HSCROLL   0x00100000L MENUP MENU {  POPUP "&Start the program"  {  MENUITEM "S&tart", 200  MENUITEM "E&xit the program", 300  } } // Dialog box definition DIAL1 DIALOG 0, 0, 200, 140 STYLE WS_SYSMENU  DS_3DLOOK CAPTION "Example of PIPE use" FONT 8, "Arial" { CONTROL "", 101, "edit", ES_LEFT  ES_MULTILINE  WS_VISIBLE  WS_BORDER WS_VSCROLL  WS_HSCROLL, 24, 20, 128, 70 } ; The PIPE.INC file ; Constants SW_HIDE               equ 0 SW_SHOWNORMAL         equ 1 STARTFJJSESHOWWINDOW  equ 1h STARTF_USESTDHANDLES  equ 100h STARTF_ADD = STARTFUSESHOWWINDOW + STARTF_USESTDHANDLES ; This message arrives when the window is closed WM_CLOSE              equ 10h WM_INITDIALOG         equ 110h WM_COMMAND            equ 111h EM_REPLACESEL         equ 0C2h ; Prototypes of external procedures IFDEF MASM        EXTERN ReadFile@20:NEAR        EXTERN CloseHandle@4:NEAR        EXTERN CreatePipe@16:NEAR        EXTERN SetMenu@8:NEAR        EXTERN LoadMenuA@8:NEAR        EXTERN CreateProcessA@40:NEAR        EXTERN ExitProcess@4:NEAR        EXTERN GetModuleHandleA@4:NEAR        EXTERN DialogBoxParamA@20:NEAR        EXTERN EndDialog@8:NEAR        EXTERN SendDlgItemMessageA@20:NEAR ELSE        EXTERN ReadFile:NEAR        EXTERN CloseHandle:NEAR        EXTERN CreatePipe:NEAR        EXTERN TerminateProcess: NEAR        EXTERN WaitForSingleObject:NEAR        EXTERN SetMenu:NEAR        EXTERN LoadMenuA:NEAR        EXTERN CreateProcessA:NEAR        EXTERN ExitProcess:NEAR        EXTERN GetModuleHandleA:NEAR        EXTERN DialogBoxParamA:NEAR        EXTERN EndDialog:NEAR        EXTERN SendDlgItemMessageA:NEAR        ReadFile@20 = ReadFile        CloseHandle@4 = CloseHandle        CreatePipe@16 = CreatePipe        TerminateProcess@8 = TerminateProcess        WaitForSingleObject@8 = WaitForSingleObject        SetMenu@8 = SetMenu        LoadMenuA@8 = LoadMenuA        CreateProcessA@40 = CreateProcessA        ExitProcess@4 = ExitProcess        GetModuleHandleA@4 = GetModuleHandleA        DialogBoxParamA@20 = DialogBoxParamA        EndDialog@8 = EndDialog        SendDlgItemMessageA@20 = SendDlgItemMessageA ENDIF ; Structures ; Message structure MSGSTRUCT STRUC        MSHWND    DD ?        MSMESSAGE DD ?        MSWPARAM  DD ?        MSLPARAM  DD ?        MSTIME    DD ?        MSPT      DD ? MSGSTRUCT ENDS ; Structure for CreateProcess STARTUP STRUC        cb              DD 0        lpReserved      DD 0        lpDesktop       DD 0        lpTitle         DD 0        dwX             DD 0        dwY             DD 0        dwXSize         DD 0        dwYSize         DD 0        dwXCountChars   DD 0        dwYCountChars   DD 0        dwFillAttribute DD 0        dwFlags         DD 0        wShowWindow     DW 0        cbReserved2     DW 0        lpReserved2     DD 0        hStdInput       DD 0        hStdOutput      DD 0        hStdError       DD 0 STARTUP ENDS ; Structure - Information about the process PROCINF STRUC        hProcess        DD ?        hThread         DD ?        Idproc          DD ?        idThr           DD ? PROCINF ENDS ; The PIPE.ASM file .586P ; Flat memory model .MODEL FLAT, stdcall include pipe.inc ; INCLUDELIB directives for the linker IFDEF MASM        includelib c:\masm32\lib\user32.lib        includelib c:\masm32\lib\kernel32.lib ELSE        includelib c:\tasm32\lib\import32.lib ENDIF ;--------------------------------------------- ; Data segment _DATA SEGMENT        STRUP  STARTUP  <?>        INF    PROCINF  <?>        MSG    MSGSTRUCT  <?>        HINST  DD 0 ; Application descriptor        PA     DB "DIAL1", 0        CMD    DB "c:\tasm32\bin\tlink32.exe", 0        PMENU  DB "MENUP", 0        HW     DD ?        HR     DD ?        BUFER  DB 3000 DUP(0)        BYT    DD ? _DATA ENDS ; Code segment _TEXT SEGMENT START: ; Get the application handle        PUSH   0        CALL   GetModuleHandleA@4        MOV    [HINST], EAX ;--------------------------------        PUSH   0        PUSH   OFFSET WNDPROC        PUSH   0        PUSH   OFFSET PA        PUSH   [HINST]        CALL   DialogBoxParamA@20        CMP    EAX, -1        JNE    KOL ; Error message KOL: ;-------------------------------        PUSH  0        CALL  ExitProcess@4 ;------------------------------- ; Window procedure ; Position of parameters in the stack ; [BP+014H] ; LPARAM ; [BP+10H]  ; WAPARAM ; [BP+0CH]  ; MES ; [BP+8]    ; HWND WNDPROC  PROC        PUSH  EBP        MOV   EBP, ESP        PUSH  EBX        PUSH  ESI        PUSH  EDI -----------------        CMP   DWORD PTR [EBP+0CH], WM_CLOSE        JNE   L1 L3:        PUSH  0        PUSH  DWORD PTR [EBP+08H]        CALL  EndDialog@8        JMP   FINISH L1:        CMP   DWORD PTR [EBP+0CH], WM_INITDIALOG        JNE  L2 ; Load the menu        PUSH  OFFSET PMENU        PUSH  [HINST]        CALL  LoadMenuA@8 ; Set the menu        PUSH  EAX        PUSH  DWORD PTR [EBP+08H]        CALL  SetMenu@8        JMP   FINISH L2:        CMP   DWORD PTR [EBP+0CH], WM_COMMAND        JNE   FINISH        CMP   WORD PTR [EBP+10H], 300        JE    L3        CMP   WORD PTR [EBP+10H], 200        JNE   FINISH ; Startup here ; PIPE in the beginning        PUSH  0        PUSH  0        PUSH  OFFSET HW        PUSH  OFFSET HR        CALL  CreatePipe@16        MOV   EAX, HW ; Console application starts here        MOV   STRUP.cb, 68        MOV   STRUP.lpReserved, 0        MOV   STRUP.lpDesktop, 0        MOV   STRUP.lpTitle, 0        MOV   STRUP.dwFlags, STARTF_ADD        MOV   STRUP.cbReserved2, 0        MOV   STRUP.lpReserved2, 0        MOV   STRUP.wShowWindow, SW_HIDE ; Process window is invisible        MOV   STRUP.hStdOutput, EAX        MOV   STRUP.hStdError, EAX ;------------------------------        PUSH  OFFSET INF        PUSH  OFFSET STRUP        PUSH  0        PUSH  0        PUSH  0        PUSH  1 ; Inherit descriptors        PUSH  0        PUSH  0        PUSH  OFFSET CMD        PUSH  0        CALL  CreateProcessA@40 ; Read information        PUSH  0        PUSH  OFFSET BYT        PUSH  3000        PUSH  OFFSET BUFER        PUSH  HR        CALL  ReadFile@20        PUSH  OFFSET BUFER        PUSH  0        PUSH  EM_REPLACESEL        PUSH  101        PUSH  DWORD PTR [EBP+08H]        CALL  SendDlgItemMessageA@20 ; Close the handle for writing        PUSH  HW        CALL  CloseHandle@4 ; Close the handle for reading        PUSH  HR        CALL  CloseHandle@4 FINISH:        MOV   EAX, 0        POP   EDI        POP   ESI        POP   EBX        POP   EBP        RET   16 WNDPROC  ENDP _TEXT ENDS END START 

 

The underlying idea of pipes is easy. When creating a process, it is possible to assign it the appropriate pipe descriptor as the input or the output descriptor. After that, it will be possible to organize information exchange between two processes using the WriteFile and ReadFile functions.

To translate the program presented in Listing 18.3, issue the following commands using MASM32:

 ml /c /coff /DMASM pipe.asm     rc pipe.rc     link /subsystem:windows pipe.obj pipe.res 

Issue the following commands using TASM32:

 tasm32 /ml pipe.asm     brcc32 pipe.rc     tlink32 -aa pipe.obj,,,,,pipe.res 

The program that you just considered requires some comments.

Starting a console application is a complicated task. Therefore, I won't dive into details. In the program in Listing 18.3, this procedure is practically no different from the one used in Chapter 15 for starting the WINWORD.EXE application. Consider, however, new features implemented in this program. Note that the EditBox control plays an interesting role here. This window element plays the role of the output console. To achieve this, set the ES_MULTILINE property, which displays the entire text sent to the window using the EM_REPLACESEL message. To read the information, a large buffer is used. Principally, it is possible to read the data in smaller portions, checking the number of read bytes as with files.

^[i] So-called named pipes are implemented in Windows NT.