130 lines
4.2 KiB
C++
130 lines
4.2 KiB
C++
/** @example concurrency.cc
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*
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* A simple example of the concurrency module usage, explaining schdulers,
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* ostd::spawn(), ostd::tid as well as ostd::channel.
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*/
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#include <ostd/io.hh>
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#include <ostd/concurrency.hh>
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using namespace ostd;
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/* this version uses Go-style channels to exchange data; multiple
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* tasks can put data into channels, the channel itself is a thread
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* safe queue; it goes the other way around too, multiple tasks can
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* wait on a channel for some data to be received
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*/
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template<typename Slice>
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static void test_channel(Slice first_half, Slice second_half) {
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auto c = make_channel<int>();
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auto f = [](auto ch, auto half) {
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ch.put(foldl(half, 0));
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};
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spawn(f, c, first_half);
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spawn(f, c, second_half);
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int a = c.get();
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int b = c.get();
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writefln(" %s + %s = %s", a, b, a + b);
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}
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/* this version uses future-style tid objects that represent the tasks
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* themselves including the return value of the task; the return value
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* can be retrieved using .get(), which will wait for the value to be
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* stored unless it already is, becoming invalid after retrieval of
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* the value; the tid also intercepts any possible exceptions thrown
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* by the task and propagates them in .get(), allowing the user to
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* perform safe exception handling across tasks
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*
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* keep in mind that unlike the above, this will always wait for t1
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* first (though t2 can still run in parallel to it depending on the
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* scheduler currently in use), so a will always come from t1 and b
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* from t2; in the above test, a can come from either task
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*/
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template<typename Slice>
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static void test_tid(Slice first_half, Slice second_half) {
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auto f = [](auto half) {
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return foldl(half, 0);
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};
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auto t1 = spawn(f, first_half);
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auto t2 = spawn(f, second_half);
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int a = t1.get();
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int b = t2.get();
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writefln(" %s + %s = %s", a, b, a + b);
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}
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static void test_all() {
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/* have an array, split it in two halves and sum each half in a separate
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* task, which may or may not run in parallel with the other one depending
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* on the scheduler currently in use - several schedulers are shown
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*/
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static auto input = { 150, 38, 76, 25, 67, 18, -15, 215, 25, -10 };
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static auto first_half = iter(input).slice(0, input.size() / 2);
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static auto second_half = iter(input).slice(input.size() / 2);
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writeln(" testing channels...");
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test_channel(first_half, second_half);
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writeln(" testing futures...");
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test_tid(first_half, second_half);
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}
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int main() {
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/* using thread_scheduler results in an OS thread spawned per task,
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* implementing a 1:1 (kernel-level) scheduling - very expensive on
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* Windows, less expensive on Unix-likes (but more than coroutines)
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*/
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thread_scheduler{}.start([]() {
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writeln("(1) 1:1 scheduler: starting...");
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test_all();
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writeln("(1) 1:1 scheduler: finishing...");
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});
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writeln();
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/* using simple_coroutine_scheduler results in a coroutine spawned
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* per task, implementing N:1 (user-level) scheduling - very cheap
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* and portable everywhere but obviously limited to only one thread
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*/
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simple_coroutine_scheduler{}.start([]() {
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writeln("(2) N:1 scheduler: starting...");
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test_all();
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writeln("(2) N:1 scheduler: finishing...");
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});
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writeln();
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/* using coroutine_scheduler results in a coroutine spawned per
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* task, but mapped onto a certain number of OS threads, implementing
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* a hybrid M:N approach - this benefits from multicore systems and
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* also is relatively cheap (you can create a big number of tasks)
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*/
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coroutine_scheduler{}.start([]() {
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writeln("(3) M:N scheduler: starting...");
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test_all();
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writeln("(3) M:N scheduler: finishing...");
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});
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}
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/*
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(1) 1:1 scheduler: starting...
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testing channels...
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356 + 233 = 589
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testing futures...
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356 + 233 = 589
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(1) 1:1 scheduler: finishing...
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(2) N:1 scheduler: starting...
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testing channels...
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356 + 233 = 589
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testing futures...
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356 + 233 = 589
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(2) N:1 scheduler: finishing...
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(3) M:N scheduler: starting...
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testing channels...
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356 + 233 = 589
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testing futures...
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356 + 233 = 589
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(3) M:N scheduler: finishing...
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*/
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