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132 lines
3.4 KiB
Markdown
132 lines
3.4 KiB
Markdown
[← Home](../README.md) · [Exec Kernel](README.md)
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# Signals — AllocSignal, SetSignal, Wait
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## Overview
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Signals are the lightest AmigaOS synchronization primitive. Each task has 32 signal bits (`tc_SigAlloc`). A task blocks on `Wait(mask)` until any of the specified bits are set by another task or interrupt handler calling `Signal()`.
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---
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## Signal Bit Constants
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```c
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/* exec/tasks.h — NDK39 */
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/* Bits 0–15: application-allocated via AllocSignal() */
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/* Bits 16–31: reserved by exec */
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#define SIGB_ABORT 0 /* bit 0: break signal */
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#define SIGB_CHILD 1 /* bit 1: child task signal */
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#define SIGB_BLIT 4 /* bit 4: blitter done (exec internal) */
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#define SIGB_SINGLE 4 /* alias */
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#define SIGB_INTUITION 5 /* bit 5: Intuition events (exec internal) */
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#define SIGB_DOS 8 /* bit 8: DOS signal */
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/* Workbench/DOS break signals (bits 12–15): */
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#define SIGBREAKB_CTRL_C 12
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#define SIGBREAKB_CTRL_D 13
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#define SIGBREAKB_CTRL_E 14
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#define SIGBREAKB_CTRL_F 15
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#define SIGBREAKF_CTRL_C (1L<<SIGBREAKB_CTRL_C) /* $1000 */
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#define SIGBREAKF_CTRL_D (1L<<SIGBREAKB_CTRL_D) /* $2000 */
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#define SIGBREAKF_CTRL_E (1L<<SIGBREAKB_CTRL_E) /* $4000 */
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#define SIGBREAKF_CTRL_F (1L<<SIGBREAKB_CTRL_F) /* $8000 */
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```
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---
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## Allocating and Freeing Signals
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```c
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/* Allocate an unused signal bit (-1 = any free bit): */
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LONG sigBit = AllocSignal(-1); /* LVO -246 */
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if (sigBit < 0) { /* all 16 user bits in use */ }
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ULONG sigMask = (1L << sigBit);
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/* Free when done: */
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FreeSignal(sigBit); /* LVO -252 */
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```
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---
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## Waiting for Signals
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```c
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/* Block until any of the listed signals arrive: */
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ULONG received = Wait(sigMask | SIGBREAKF_CTRL_C); /* LVO -318 */
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if (received & SIGBREAKF_CTRL_C) {
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/* user pressed CTRL-C */
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cleanup_and_exit();
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}
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if (received & sigMask) {
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/* our custom event occurred */
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}
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```
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`Wait()` returns only after at least one bit in the mask is set. It is equivalent to sleeping — the task is moved to `TaskWait` and no CPU is consumed.
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---
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## Sending Signals
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```c
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/* Signal a task from another task or interrupt handler: */
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Signal(target_task, sigMask); /* LVO -324 */
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```
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`Signal()` is safe from interrupt context.
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---
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## SetSignal — Read and Clear
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```c
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/* Read and clear specific signal bits atomically: */
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ULONG old = SetSignal(new_bits, change_mask); /* LVO -306 */
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/* old = previous state of all 32 signal bits */
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/* new value = (old & ~change_mask) | (new_bits & change_mask) */
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/* Check CTRL-C without blocking: */
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if (SetSignal(0, SIGBREAKF_CTRL_C) & SIGBREAKF_CTRL_C) {
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/* CTRL-C was pending — now cleared */
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}
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```
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---
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## Typical Usage Pattern: Event Loop
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```c
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struct MsgPort *port = CreateMsgPort();
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ULONG portSig = (1L << port->mp_SigBit);
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ULONG waitMask = portSig | SIGBREAKF_CTRL_C;
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BOOL running = TRUE;
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while (running) {
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ULONG sigs = Wait(waitMask);
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if (sigs & SIGBREAKF_CTRL_C) {
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running = FALSE;
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}
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if (sigs & portSig) {
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struct Message *msg;
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while ((msg = GetMsg(port)) != NULL) {
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/* handle message */
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ReplyMsg(msg);
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}
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}
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}
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DeleteMsgPort(port);
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```
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---
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## References
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- NDK39: `exec/tasks.h`, `exec/execbase.h`
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- ADCD 2.1: `AllocSignal`, `FreeSignal`, `Signal`, `Wait`, `SetSignal`
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- [tasks_processes.md](tasks_processes.md) — tc_SigAlloc, tc_SigRecvd fields
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- *Amiga ROM Kernel Reference Manual: Exec* — signals chapter
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