Squashed 'third_party/marl/' changes from 64d123947..ca8408f68

ca8408f68 Scheduler: Reduce the number of mutex locks / unlock.
575b61e76 Fix compilation of marl::Ticket::onCall()
e9f312688 waitForWork(): Early out if there work.num > 0
3196a0539 Scheduler: Use std::deque instead of std::queue
08a820171 Add flags to marl::Task
cb3c481d0 Scheduler: Use a separate flag to indicate whether to call notify()
598c993ec marl::ConditionVariable - use containers::list
d0c501a9c Add marl::containers::list
aa1de9091 Benchmarks: Add EventBaton

git-subtree-dir: third_party/marl
git-subtree-split: ca8408f6890ff447eb5f90d663149f3327b1607e
13 files changed
tree: e5e86c2eb5f4d4a52e536cd15d522dd31a933817
  1. docs/
  2. examples/
  3. include/
  4. kokoro/
  5. src/
  6. third_party/
  7. tools/
  8. .clang-format
  9. .gitignore
  10. .gitmodules
  11. AUTHORS
  12. BUILD.bazel
  13. CMakeLists.txt
  14. CONTRIBUTING.md
  15. LICENSE
  16. README.md
  17. WORKSPACE
README.md

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 "marl/waitgroup.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.

  constexpr int numTasks = 10;

  // Create an event that is manually reset.
  marl::Event sayHellow(marl::Event::Mode::Manual);

  // Create a WaitGroup with an initial count of numTasks.
  marl::WaitGroup saidHellow(numTasks);

  // Schedule some tasks to run asynchronously.
  for (int i = 0; i < numTasks; i++) {
    // Each task will run on one of the 4 worker threads.
    marl::schedule([=] {  // All marl primitives are capture-by-value.
      // Decrement the WaitGroup counter when the task has finished.
      defer(saidHellow.done());

      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);
    });
  }

  sayHellow.signal();  // Unblock all the tasks.

  saidHellow.wait();  // Wait for all tasks to complete.

  printf("All tasks said hello.\n");

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

Benchmarks

Graphs of several microbenchmarks can be found here.

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})

Note: This is not an officially supported Google product