taskloom

A small header-only C++20 concurrency library centered on a work-stealing deque, with the supporting modules a task scheduler needs around one.

taskloom is not a scheduler or a thread pool: it is the data structures a scheduler is assembled from. Each header is usable on its own, depends only on the standard library, and documents its memory-ordering contract in place.

Modules

• taskloom/wsq.hpp: Chase-Lev work-stealing deque: one owner pushes and pops, any number of thieves steal, lock-free stealing with safe ring growth
• taskloom/rwlock.hpp: reader-writer spinlock with a seq_cst acquisition protocol; composes with std::shared_lock and std::unique_lock
• taskloom/event.hpp: dependency-graph completion nodes: a node fires once its last prerequisite completes, with race-safe edge addition
• taskloom/stats.hpp: constant-space streaming statistics whose merge preserves variance across threads
• taskloom/atomic.hpp: padded<T> false-sharing isolation and lock-free compile-time guarantees
• taskloom/hw.hpp: cache-line and page constants, spin hint, tick counter

Quick start

include(FetchContent)
FetchContent_Declare(taskloom
  GIT_REPOSITORY https://github.com/jasoneplumb/taskloom.git
  GIT_TAG v0.1.0
)
FetchContent_MakeAvailable(taskloom)
target_link_libraries(app PRIVATE taskloom::taskloom)

#include <taskloom/wsq.hpp>

taskloom::wsq<Task*> queue;

// Owner thread:
queue.push(task);
if (auto mine = queue.pop()) { run(*mine); }

// Any other worker:
if (auto stolen = queue.steal()) { run(*stolen); }

Dependency tracking with event:

#include <taskloom/event.hpp>

struct node : taskloom::event {
  void on_ready() noexcept override { /* every prerequisite completed */ }
};

node upload, shaders, frame;
frame.depends_on(upload);
frame.depends_on(shaders);
upload.complete();
shaders.complete();  // Last prerequisite: frame.on_ready() fires here.

Building and testing

cmake -S . -B build -DCMAKE_BUILD_TYPE=Release
cmake --build build --parallel
ctest --test-dir build --output-on-failure

Tests run under ThreadSanitizer with -DTASKLOOM_SANITIZE=thread; CI covers macOS, Linux, and Windows (MSVC) plus a TSan job. Benchmarks live in bench/ and are conservation-checked: a reported number is a verified number.

Design

Trade-off rationale and same-machine measurements, including the comparison against a mutex-guarded std::deque, are in docs/design.md.

License

MIT