Stateful Goroutines in Cilk

#include <cilk/cilk.h>
#include <iostream>
#include <map>
#include <random>
#include <atomic>
#include <chrono>
#include <thread>

struct ReadOp {
    int key;
    int* result;
};

struct WriteOp {
    int key;
    int val;
    bool* result;
};

int main() {
    std::atomic<uint64_t> readOps(0);
    std::atomic<uint64_t> writeOps(0);

    std::map<int, int> state;
    
    auto stateManager = [&]() {
        while (true) {
            ReadOp* readOp = nullptr;
            WriteOp* writeOp = nullptr;
            
            if (cilk_spawn [&]() -> ReadOp* {
                ReadOp* op = new ReadOp{rand() % 5, new int};
                *op->result = state[op->key];
                return op;
            }()) {
                readOp = _cilk_spawn_result;
            } else if (cilk_spawn [&]() -> WriteOp* {
                WriteOp* op = new WriteOp{rand() % 5, rand() % 100, new bool};
                state[op->key] = op->val;
                *op->result = true;
                return op;
            }()) {
                writeOp = _cilk_spawn_result;
            }
            
            if (readOp) {
                readOps++;
                delete readOp->result;
                delete readOp;
            } else if (writeOp) {
                writeOps++;
                delete writeOp->result;
                delete writeOp;
            }
            
            std::this_thread::sleep_for(std::chrono::milliseconds(1));
        }
    };

    cilk_spawn stateManager();

    for (int r = 0; r < 100; r++) {
        cilk_spawn [&]() {
            while (true) {
                ReadOp op{rand() % 5, new int};
                cilk_spawn [&]() {
                    *op.result = state[op.key];
                }();
                cilk_sync;
                readOps++;
                delete op.result;
                std::this_thread::sleep_for(std::chrono::milliseconds(1));
            }
        }();
    }

    for (int w = 0; w < 10; w++) {
        cilk_spawn [&]() {
            while (true) {
                WriteOp op{rand() % 5, rand() % 100, new bool};
                cilk_spawn [&]() {
                    state[op.key] = op.val;
                    *op.result = true;
                }();
                cilk_sync;
                writeOps++;
                delete op.result;
                std::this_thread::sleep_for(std::chrono::milliseconds(1));
            }
        }();
    }

    std::this_thread::sleep_for(std::chrono::seconds(1));

    uint64_t readOpsFinal = readOps.load();
    std::cout << "readOps: " << readOpsFinal << std::endl;
    uint64_t writeOpsFinal = writeOps.load();
    std::cout << "writeOps: " << writeOpsFinal << std::endl;

    return 0;
}

In this example, we use Cilk’s parallel programming features to manage state across multiple threads. This approach aligns with Cilk’s ideas of sharing memory by communicating and having each piece of data owned by exactly one thread.

The ReadOp and WriteOp structs encapsulate read and write requests, respectively. The stateManager function owns the state, which is a map private to this thread. It repeatedly selects between read and write operations, responding to requests as they arrive.

We start 100 threads to issue reads and 10 threads to issue writes to the state-owning thread. Each read or write operation is performed using cilk_spawn, which allows for parallel execution.

The program runs for one second, after which it reports the number of read and write operations performed.

To compile and run this Cilk program:

$ clang++ -fcilkplus stateful_threads.cpp -o stateful_threads
$ ./stateful_threads
readOps: 71708
writeOps: 7177

Running our program shows that the Cilk-based state management example completes about 80,000 total operations.

This Cilk-based approach leverages the language’s built-in parallelism features. It might be particularly useful in cases where you have other parallel computations involved or when managing multiple mutexes would be error-prone. You should use whichever approach feels most natural, especially with respect to understanding the correctness of your program.

Mutexes in Cilk

Sorting in Cilk

Learn X By Example

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Stateful Goroutines in Cilk