Marl

Marl is a hybrid thread / fiber task scheduler written in C++ 11.

About

Marl is a C++ 11 library that provides a fluent interface for running tasks across a number of threads.

Marl uses a combination of fibers and threads to allow efficient execution of tasks that can block, while keeping a fixed number of hardware threads.

Marl supports Windows, macOS, Linux, Fuchsia and Android (arm, aarch64, mips64, ppc64 (ELFv2), x86 and x64).

Marl has no dependencies on other libraries (with an exception on googletest for building the optional unit tests).

Example:

#include "marl/defer.h"
#include "marl/event.h"
#include "marl/scheduler.h"

#include <cstdio>

int main() {
  // Create a marl scheduler using the 4 hardware threads.
  // Bind this scheduler to the main thread so we can call marl::schedule()
  marl::Scheduler scheduler;
  scheduler.bind();
  scheduler.setWorkerThreadCount(4);
  defer(scheduler.unbind());  // Automatically unbind before returning.

  // Create an event that automatically resets itself.
  marl::Event sayHellow(marl::Event::Mode::Auto);
  marl::Event saidHellow(marl::Event::Mode::Auto);

  // Schedule some tasks to run asynchronously.
  for (int i = 0; i < 10; i++) {
    // Each task will run on one of the 4 worker threads.
    marl::schedule([=] {  // All marl primitives are capture-by-value.
      printf("Task %d waiting to say hello!\n", i);

      // Blocking in a task?
      // The scheduler will find something else for this thread to do.
      sayHellow.wait();

      printf("Hello from task %d!\n", i);

      saidHellow.signal();
    });
  }

  // Unblock the tasks one by one.
  for (int i = 0; i < 10; i++) {
    sayHellow.signal();
    saidHellow.wait();
  }

  // All tasks are guaranteed to completed before the scheduler is destructed.
}

Building

Marl contains many unit tests and examples that can be built using CMake.

Unit tests require fetching the googletest external project, which can be done by typing the following in your terminal:

cd <path-to-marl>
git submodule update --init

Linux and macOS

To build the unit tests and examples, type the following in your terminal:

cd <path-to-marl>
mkdir build
cd build
cmake .. -DMARL_BUILD_EXAMPLES=1 -DMARL_BUILD_TESTS=1
make

The resulting binaries will be found in <path-to-marl>/build

Windows

Marl can be built using Visual Studio 2019's CMake integration.

Using Marl in your CMake project

You can build and link Marl using add_subdirectory() in your project's CMakeLists.txt file:

set(MARL_DIR <path-to-marl>) # example <path-to-marl>: "${CMAKE_CURRENT_SOURCE_DIR}/third_party/marl"
add_subdirectory(${MARL_DIR})

This will define the marl library target, which you can pass to target_link_libraries():

target_link_libraries(<target> marl) # replace <target> with the name of your project's target

You may also wish to specify your own paths to the third party libraries used by marl. You can do this by setting any of the following variables before the call to add_subdirectory():

set(MARL_THIRD_PARTY_DIR <third-party-root-directory>) # defaults to ${MARL_DIR}/third_party
set(MARL_GOOGLETEST_DIR  <path-to-googletest>)         # defaults to ${MARL_THIRD_PARTY_DIR}/googletest
add_subdirectory(${MARL_DIR})

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Note: This is not an officially supported Google product