user
92 lines
2.9 KiB
Markdown
92 lines
2.9 KiB
Markdown
# K03 — FreeRTOS C++ `VectorV1`: move ownership and RAII
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K03 starts from the deliberately incomplete `Vector V0`: one object owns a
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`new double[]` buffer, but has no destructor and could be shallow-copied. The
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card introduces one invariant:
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> Every live buffer has exactly one owner; a moved-from vector is empty.
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The implementation in [`include/freertos/vector_v1.hpp`](include/freertos/vector_v1.hpp)
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adds:
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- a destructor that releases the array;
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- deleted copy construction and copy assignment;
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- `noexcept` move construction;
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- `noexcept` move assignment that first releases the destination's old buffer;
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- an explicit, testable empty state: `data() == nullptr && size() == 0`.
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The kernel and `heap_4.c` remain C. The one C++ linkage unit
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[`src/common/cpp_heap.cpp`](src/common/cpp_heap.cpp) maps scalar/array and
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sized/unsized `new`/`delete` to `pvPortMalloc()` and `vPortFree()`.
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## One executable, seven checkpoints
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`task01_vector_raii` creates a four-element source and a two-element
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destination. Move assignment must release the destination buffer before it
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takes the source buffer. A later move construction transfers the same address
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again, and the final destructor returns the heap to its baseline.
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| Checkpoint | Evidence |
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| --- | --- |
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| 1 | initialized heap baseline |
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| 2 | source owns buffer A |
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| 3 | destination owns buffer B; two live allocations |
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| 4 | B released, destination owns A, source empty |
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| 5 | final owner owns A, previous destination empty |
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| 6 | final owner destroyed; heap already equals baseline |
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| 7 | two allocations, two frees, zero live owners, PASS |
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## Build and verify
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The local fallback obtains Hazard3 startup files and simulator from the
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neighboring FreeRTOS C scheduler card. A standalone environment can be passed
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with `RV_ENV_ROOT` and `TB`.
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```sh
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make check
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```
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Expected summary:
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```text
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PASS host: move-only VectorV1, self-move and destructor safety
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PASS ABI: no RTTI/vtable/hosted runtime; complete new/delete bridge
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PASS task01: Vector V1 move ownership + RAII
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```
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The host test uses ASan/UBSan and also proves that a copy attempt fails to
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compile. The cross-build is freestanding C++17 with exceptions and RTTI
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disabled. Hazard3 runs the real upstream `heap_4.c`.
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## Debug
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```gdb
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b vector_raii_debug_checkpoint
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p g_last_checkpoint
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p/x g_source_buffer_before_move
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p/x g_destination_old_buffer
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p/x g_destination_buffer_after_assignment
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p/x g_final_buffer_after_construction
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p g_cpp_allocation_count
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p g_cpp_deallocation_count
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p g_cpp_live_allocations
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p g_initial_free
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p g_after_two_owners_free
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p g_after_scope_free
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p g_minimum_ever_free
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```
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## Scope boundary
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This card teaches ownership transfer, not a production container. `VectorV1`
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does not grow, check bounds, select an allocator, or start a task. RAII works
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when C++ scopes leave normally; it does not make forced `vTaskDelete()` or a
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system halt unwind arbitrary task-local objects.
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Render the printable card with:
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```sh
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make pdf
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```
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