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fix: park nodes on a full output instead of blocking the worker
push_blocking parked a scheduler worker inside the push. Nodes own a
private single-thread pool, so the parked thread was the only one that
could drain that node's own input — hold-and-wait, and under sustained
backpressure four nodes of a five-node chain slept in nanosleep at once.
channel.hpp already warned about this for sentinels; it applies just as
much to data pushes.

The scheduler was purely input-driven: on_input_ready() wakes a node when
input arrives, with no counterpart for "my output has room". Lacking that
signal, blocking the thread was the only way to handle a full output.
This adds the missing half.

- Channel::try_push + has_space + set_space_callback; the callback fires
  from both pop() and try_pop_now().
- PoolNode/PoolObjectNode keep a one-slot pending_ buffer with per-element
  done flags, so a retry cannot duplicate an already-accepted element. One
  slot suffices because queued_ admits at most one fire_once per node.
- The re-check after clearing queued_ closes the lost-wakeup race where a
  space callback fires while the flag is still up and is swallowed.

Two bugs surfaced once nodes actually parked, both fixed here:

- pop_one reports an *empty* channel as ChannelClosedError, which is also
  the node's "upstream finished, self-stop" signal. A node woken by output
  space with empty inputs therefore killed itself. fire_once now releases
  the worker when its inputs are not ready rather than falling through.
- The drained-park path resubmitted unconditionally instead of via
  on_input_ready(), firing nodes with nothing to read.

compute_priority is now output-aware: mean output fill is deducted from
mean input fill, mapped as 0.5·(1 + in - out). Input fill alone asks only
"how much work is waiting for me"; a node whose outputs are already full
cannot deliver, so running it just parks it again and wastes the slot
while the node that would drain that channel waits behind it. The
scheduler now favours whoever is furthest downstream of a bottleneck.

Also adds a network-level error listener. A node's exception was discarded
at the node boundary and survived only as a Closed event, which reports
that a node stopped but not why — that missing detail is what made the
above slow to diagnose. INode::set_network_error_callback plus
StaticNetwork::set_error_handler forward it to the application.

Tests: 121/121. test_backpressure_deadlock drives a five-node chain with
capacity-2 channels against a slow sink and fails on the old code. The
four test_pool_node overflow tests now assert parking rather than the
removed drop-and-report behaviour.

Known-incomplete: a rare hang remains, roughly 1 run in 20 against a 300s
timeout, down from every run failing. Committed because the fix is a large
strict improvement and the residual case needs its own reproduction.
2026-07-31 22:40:07 +02:00

79 lines
3.4 KiB
CMake

cmake_minimum_required(VERSION 3.21)
# ── Catch2 ────────────────────────────────────────────────────────────────────
find_package(Catch2 3 QUIET)
if(NOT Catch2_FOUND)
include(FetchContent)
FetchContent_Declare(
Catch2
GIT_REPOSITORY https://github.com/catchorg/Catch2.git
GIT_TAG v3.5.3
)
FetchContent_MakeAvailable(Catch2)
endif()
# ── Google Test ───────────────────────────────────────────────────────────────
find_package(GTest QUIET)
if(NOT GTest_FOUND)
include(FetchContent)
FetchContent_Declare(
googletest
GIT_REPOSITORY https://github.com/google/googletest.git
GIT_TAG v1.14.0
)
FetchContent_MakeAvailable(googletest)
endif()
# ── Test executable ───────────────────────────────────────────────────────────
add_executable(kpn_tests
test_fixed_string.cpp
test_traits.cpp
test_channel.cpp
test_node.cpp
test_network.cpp
test_static_network.cpp
test_shared_resource.cpp
test_pool_node.cpp
test_backpressure_deadlock.cpp
test_scheduler.cpp
)
target_link_libraries(kpn_tests PRIVATE
kpn
Catch2::Catch2WithMain
GTest::gtest
)
# ── Channel stress suite (separate executable) ────────────────────────────────
# Contended SPSC tests for the lock-free Channel<T>. Kept out of kpn_tests
# because each case runs many reps / tens of thousands of items and is slow.
# Most valuable under -DKPN_SANITIZER=thread, but correct (and run) without it.
add_executable(kpn_tests_stress test_channel_stress.cpp)
target_link_libraries(kpn_tests_stress PRIVATE kpn Catch2::Catch2WithMain)
# ── Sanitizer flags ───────────────────────────────────────────────────────────
# kpn_sanitizer_flags() is defined in the top-level CMakeLists and is a no-op
# unless -DKPN_SANITIZER=... is set. Sanitizer must be on both compile and link.
kpn_sanitizer_flags(_kpn_san)
if(_kpn_san)
foreach(_t kpn_tests kpn_tests_stress)
target_compile_options(${_t} PRIVATE ${_kpn_san})
target_link_options(${_t} PRIVATE ${_kpn_san})
endforeach()
endif()
include(CTest)
include(Catch)
# DISCOVERY_MODE PRE_TEST defers test enumeration to `ctest` run time. The
# default (POST_BUILD) runs each test binary during the build to list its
# cases — which fails a sanitizer build: a TSan/ASan binary needs a fixed
# address-space layout and aborts on startup ("unexpected memory mapping")
# under the container's ASLR, breaking the build before any test runs. The
# tsan.yaml job invokes the binaries directly (not via ctest), so deferring
# discovery costs nothing there and keeps `ctest` working for normal builds.
catch_discover_tests(kpn_tests DISCOVERY_MODE PRE_TEST)
# Register the stress suite under its own label so CI can run / time it
# separately from the fast unit tests.
catch_discover_tests(kpn_tests_stress DISCOVERY_MODE PRE_TEST PROPERTIES LABELS "stress")