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Process Management — CreateNewProc, SystemTagList, Execute

Overview

AmigaDOS provides several ways to launch child processes, ranging from the low-level CreateNewProc to the shell-level Execute and SystemTagList.

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CreateNewProcTags (OS 2.0+)

/* dos/dostags.h — NDK39 */
struct Process *proc = CreateNewProcTags(
    NP_Entry,       myFunction,     /* function pointer */
    NP_Name,        "Worker",       /* task name */
    NP_StackSize,   8192,           /* stack size in bytes */
    NP_Priority,    0,              /* scheduling priority */
    NP_Input,       Open("NIL:", MODE_OLDFILE),
    NP_Output,      Open("NIL:", MODE_NEWFILE),
    NP_CloseInput,  TRUE,           /* close input on exit */
    NP_CloseOutput, TRUE,
    NP_CurrentDir,  DupLock(currentDir),
    TAG_DONE);

Tag Constants

Tag	Value	Meaning
NP_Entry	—	Function to run as the new process
NP_Seglist	—	Alternative: run from a loaded segment list
NP_Name	—	Process name (appears in task list)
NP_StackSize	—	Stack size in bytes (default 4096)
NP_Priority	—	Task priority (−128 to +127)
NP_Input	—	BPTR stdin handle
NP_Output	—	BPTR stdout handle
NP_Error	—	BPTR stderr handle (OS 3.0+)
NP_CurrentDir	—	Lock for current directory
NP_HomeDir	—	Lock for PROGDIR:
NP_CopyVars	—	Copy parent's local vars to child

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SystemTagList — Run a Shell Command

/* Execute a command string as if typed in a shell: */
LONG rc = SystemTagList("dir SYS: ALL", NULL);
/* rc = return code from the command */

/* With custom I/O: */
LONG rc = SystemTagList("list RAM:", (struct TagItem[]){
    { SYS_Input,  Open("NIL:", MODE_OLDFILE) },
    { SYS_Output, Open("RAM:output.txt", MODE_NEWFILE) },
    { TAG_DONE, 0 }
});

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Execute — Legacy Command Execution

/* dos.library LVO −132 */
BOOL Execute(STRPTR command, BPTR input, BPTR output);

• command — shell command string
• input — BPTR to additional input (0 = none)
• output — BPTR to output handle (0 = current)

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WaitForChild / Process Exit

Child processes are independent tasks. To synchronize: 1. Use a shared MsgPort — child sends a death message 2. Check pr_Result2 after the child task exits 3. Use SYS_Asynch tag with SystemTagList for fire-and-forget

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References

• NDK39: dos/dostags.h, dos/dosextens.h
• ADCD 2.1: CreateNewProc, SystemTagList, Execute
• tasks_processes.md — Task/Process structures