not thread-safe. The only method in Tornado that is safe to call from other threads is IOLoop.add_callback. You can also use IOLoop.run_in_executor to asynchronously run a blocking function on another thread There are many styles of asynchronous interfaces: • Callback argument • Return a placeholder (Future, Promise, Deferred) • Deliver to a queue • Callback registry (e.g. POSIX signals) Regardless of which http_client.fetch(url) def on_fetch(f): my_future.set_result(f.result().body) fetch_future.add_done_callback(on_fetch) return my_future Notice that the coroutine returns its Future before the fetch is done

Practice ## DMITRY PROKOPTSEV ## Challenges when onboarding coroutines A lot of existing code mostly callback-based A custom-built I/O event loop predates Asio by a decade fine-tuned for specific use cases await_ready() const noexcept Performance optimization ## Awaitable example typedef void (*ares_addrinfo_callback)(void* arg, int status, int timeouts, struct ares_addrinfo* result); void ares_getaddrinfo(ares_channel_t* const char* name, const char* service, const struct ares_addrinfo_ hints* hints, ares_addrinfo_callback, void* arg); ## Awaitable example class DNSQuery { ares_channel_t* channel; const char*

not thread-safe. The only method in Tornado that is safe to call from other threads is IOLoop.add_callback. You can also use IOLoop.run_in_executor to asynchronously run a blocking function on another thread There are many styles of asynchronous interfaces: • Callback argument • Return a placeholder (Future, Promise, Deferred) • Deliver to a queue • Callback registry (e.g. POSIX signals) Regardless of which def on_fetch(f): my_future.set_result(f.result().body) fetch_future.add_done_callback(on_fetch) return my_future Notice that the coroutine returns its Future before the fetch

not thread-safe. The only method in Tornado that is safe to call from other threads is IOLoop.add_callback. You can also use IOLoop.run_in_executor to asynchronously run a blocking function on another thread There are many styles of asynchronous interfaces: • Callback argument • Return a placeholder (Future, Promise, Deferred) • Deliver to a queue • Callback registry (e.g. POSIX signals) Regardless of which def on_fetch(f): my_future.set_result(f.result().body) fetch_future.add_done_callback(on_fetch) return my_future Notice that the coroutine returns its Future before the fetch

not thread-safe. The only method in Tornado that is safe to call from other threads is IOLoop.add_callback. You can also use IOLoop.run_in_executor to asynchronously run a blocking function on another thread There are many styles of asynchronous interfaces: • Callback argument • Return a placeholder (Future, Promise, Deferred) • Deliver to a queue • Callback registry (e.g. POSIX signals) Regardless of which def on_fetch(f): my_future.set_result(f.result().body) fetch_future.add_done_callback(on_fetch) return my_future Notice that the coroutine returns its Future before the fetch

There are many styles of asynchronous interfaces: • Callback argument • Return a placeholder (Future, Promise, Deferred) • Deliver to a queue • Callback registry (e.g. POSIX signals) Regardless of which asynchronous with a callback argument: from tornado.httpclient importAsyncHTTPClient def asynchronous_fetch(url, callback): http_client =AsyncHTTPClient() def handle_response(response): callback(response callback(response.body) http_client.fetch(url, callback=handle_response) And again with a Future instead of a callback: from tornado.concurrent import Future def async_fetch_future(url): http_client =AsyncHTTPClient()

There are many styles of asynchronous interfaces: • Callback argument • Return a placeholder (Future, Promise, Deferred) • Deliver to a queue • Callback registry (e.g. POSIX signals) Regardless of which with a callback argument: from tornado.httpclient importAsyncHTTPClient def asynchronous_fetch(url, callback): http_client =AsyncHTTPClient() def handle_response(response): callback(response callback(response.body) http_client.fetch(url, callback=handle_response) And again with a Future instead of a callback: from tornado.concurrent import Future def async_fetch_future(url): http_client

not thread-safe. The only method in Tornado that is safe to call from other threads is IOLoop.add_callback. You can also use IOLoop.run_in_executor to asynchronously run a blocking function on another thread There are many styles of asynchronous interfaces: • Callback argument • Return a placeholder (Future, Promise, Deferred) • Deliver to a queue • Callback registry (e.g. POSIX signals) Regardless of which http_client.fetch(url) def on_fetch(f): my_future.set_result(f.result().body) fetch_future.add_done_callback(on_fetch) return my_future Notice that the coroutine returns its Future before the fetch is done

not thread-safe. The only method in Tornado that is safe to call from other threads is IOLoop.add_callback. You can also use IOLoop.run_in_executor to asynchronously run a blocking function on another thread There are many styles of asynchronous interfaces: • Callback argument • Return a placeholder (Future, Promise, Deferred) • Deliver to a queue • Callback registry (e.g. POSIX signals) Regardless of which def on_fetch(f): my_future.set_result(f.result().body) fetch_future.add_done_callback(on_fetch) return my_future Notice that the coroutine returns its Future before the fetch

not thread-safe. The only method in Tornado that is safe to call from other threads is IOLoop.add_callback. You can also use IOLoop.run_in_executor to asynchronously run a blocking function on another thread There are many styles of asynchronous interfaces: • Callback argument • Return a placeholder (Future, Promise, Deferred) • Deliver to a queue • Callback registry (e.g. POSIX signals) Regardless of which def on_fetch(f): my_future.set_result(f.result().body) fetch_future.add_done_callback(on_fetch) return my_future Notice that the coroutine returns its Future before the fetch