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// Copyright Vespa.ai. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
#pragma once
#include <vespa/vespalib/util/executor.h>
#include <coroutine>
#include <exception>
#include <stdexcept>
namespace vespalib::coro {
struct ScheduleFailedException : std::runtime_error {
using std::runtime_error::runtime_error;
};
// Schedule the current coroutine on the given executor. Throws an
// exception if the request was rejected by the executor.
auto schedule(Executor &executor) {
struct [[nodiscard]] awaiter {
Executor &executor;
awaiter(Executor &executor_in)
: executor(executor_in) {}
bool await_ready() const noexcept { return false; }
void await_suspend(std::coroutine_handle<> handle) __attribute__((noinline)) {
struct ResumeTask : Executor::Task {
std::coroutine_handle<> handle;
ResumeTask(std::coroutine_handle<> handle_in)
: handle(handle_in) {}
void run() override { handle.resume(); }
};
Executor::Task::UP task = std::make_unique<ResumeTask>(handle);
task = executor.execute(std::move(task));
if (task) {
throw ScheduleFailedException("rejected by executor");
}
}
void await_resume() const noexcept {}
};
return awaiter(executor);
}
// Try to schedule the current coroutine on the given executor. If the
// awaiter returns true, the coroutine is now run by the executor. If
// the awaiter returns false, the request was rejected by the executor
// and the coroutine is still running in our original context.
auto try_schedule(Executor &executor) {
struct [[nodiscard]] awaiter {
Executor &executor;
bool accepted;
awaiter(Executor &executor_in)
: executor(executor_in), accepted(true) {}
bool await_ready() const noexcept { return false; }
bool await_suspend(std::coroutine_handle<> handle) __attribute__((noinline)) {
struct ResumeTask : Executor::Task {
std::coroutine_handle<> handle;
ResumeTask(std::coroutine_handle<> handle_in)
: handle(handle_in) {}
void run() override { handle.resume(); }
};
Executor::Task::UP task = std::make_unique<ResumeTask>(handle);
task = executor.execute(std::move(task));
if (task) {
// need to start with accepted == true to avoid race
// with handle.resume() from executor thread before
// await_suspend has returned.
accepted = false;
return false;
}
return true;
}
[[nodiscard]] bool await_resume() const noexcept { return accepted; }
};
return awaiter(executor);
}
}
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