user
77 lines
2.9 KiB
Markdown
77 lines
2.9 KiB
Markdown
# K08 — DynamicTask, StaticTask, deletion and lifetime
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## Position
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- Series: FreeRTOS C++
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- Lesson: L07, card K08
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- Duration: 30 minutes
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- Real dynamic `heap_4` plus caller TCB/stack in `.bss`
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- Idle task itself and the verifier use static storage to isolate measurement
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## Outcome
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After 30 minutes the student can calculate stack words and bytes, prove dynamic
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heap cost versus zero-delta static creation, classify TCB/stack addresses, and
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explain why self-deletion and actual dynamic memory reclamation are separated by
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idle-task cleanup.
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## Lesson plan
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| Time | Mode | Evidence |
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| --- | --- | --- |
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| 0–5 | units/storage | predict 256 words, bytes and locations |
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| 5–10 | dynamic create | measure heap delta and classify TCB/stack |
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| 10–15 | static create | caller TCB/stack addresses; heap delta zero |
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| 15–20 | run/complete | identical result 500500; wrappers completed/null |
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| 20–25 | delete timing | heap still reduced immediately after self-delete |
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| 25–30 | idle cleanup | block verifier; recover exact dynamic delta/baseline |
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## Canonical timeline
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```text
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baseline
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-> xTaskCreate(dynamic): heap - dynamic_cost
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-> xTaskCreateStatic(static): no heap change
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-> both run and complete
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-> both call vTaskDelete(nullptr)
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-> verifier runs before idle: dynamic storage still pending cleanup
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-> verifier blocks
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-> idle calls termination cleanup:
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dynamic TCB/stack -> vPortFree
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static TCB/stack -> not freed (caller owned)
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-> verifier wakes: heap == baseline
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```
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## Stable evidence
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| Evidence | Required relation |
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| --- | --- |
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| dynamic cost | baseline - after_dynamic > 0 |
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| static delta | after_static == after_dynamic |
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| verifier delta | static verifier creation also leaves heap unchanged |
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| dynamic addresses | TCB and stack base lie in `ucHeap` |
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| static addresses | observed TCB/stack equal caller storage and lie outside heap |
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| before idle | free equals post-create value, despite completed wrappers |
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| after idle | free=baseline; recovered bytes=dynamic cost |
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| units | 256 `StackType_t` words = 1024 B on RV32I |
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## Main traps
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1. `stack_depth` counts words, not bytes.
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2. `vTaskDelete(nullptr)` removes the current task from scheduling but dynamic
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memory reclamation is deferred to idle.
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3. Static task deletion does not free caller storage; premature reuse is a
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lifetime bug.
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4. A wrapper handle becoming null is not proof that idle cleanup already ran.
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5. Forced deletion does not run arbitrary C++ destructors on the victim stack.
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## Acceptance
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- host test proves both create APIs receive the same stable context and static
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native handle equals caller TCB;
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- ABI proves static worker storage is `.bss` and no vtable/init runtime exists;
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- static create and verifier create have exactly zero heap delta;
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- dynamic cost is recovered only after the verifier lets idle run;
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- both results are 500500, states completed, handles null and final PASS is 1.
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