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// Copyright 2019 The Marl Authors.
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// See the License for the specific language governing permissions and
// limitations under the License.
// This is an example application that uses Marl to find and print all the prime
// numbers in the range 1 to 10000000.
#include "marl/defer.h"
#include "marl/scheduler.h"
#include "marl/thread.h"
#include "marl/ticket.h"
#include <vector>
#include <math.h>
// searchMax defines the upper limit on primes to find.
constexpr int searchMax = 10000000;
// searchChunkSize is the number of numbers searched, per task, for primes.
constexpr int searchChunkSize = 10000;
// isPrime returns true if i is prime.
bool isPrime(int i) {
auto c = static_cast<int>(sqrt(i));
for (int j = 2; j <= c; j++) {
if (i % j == 0) {
return false;
return true;
int main() {
// Create a marl scheduler using the full number of logical cpus.
// Bind this scheduler to the main thread so we can call marl::schedule()
marl::Scheduler scheduler(marl::Scheduler::Config::allCores());
defer(scheduler.unbind()); // unbind before destructing the scheduler.
// Create a ticket queue. This will be used to ensure that the primes are
// printed in ascending order.
marl::Ticket::Queue queue;
// Iterate over the range [1, searchMax] in steps of searchChunkSize.
for (int searchBase = 1; searchBase <= searchMax;
searchBase += searchChunkSize) {
// Take a ticket from the ticket queue for this task.
auto ticket = queue.take();
// Schedule the task.
marl::schedule([=] {
// Find all the primes in [searchBase, searchBase+searchChunkSize-1].
// Note this is run in parallel with the other scheduled tasks.
std::vector<int> primes;
for (int i = searchBase; i < searchBase + searchChunkSize; i++) {
if (isPrime(i)) {
// Wait until the ticket is called. This ensures that the primes are
// printed in ascending order. This may cause this task to yield and allow
// other tasks to be executed while waiting for this ticket to be called.
// Print the primes.
for (auto prime : primes) {
printf("%d is prime\n", prime);
// Call the next ticket so that those primes can be printed.
// take a ticket and wait on it to ensure that all the primes have been
// calculated and printed.
return 0;