folly::SimpleAsyncIO

SimpleAsyncIO is a wrapper around AsyncIO intended to hide all the details.

Synopsis

Declared in <folly/io/async/SimpleAsyncIO.h>

class SimpleAsyncIO
    : public EventHandler

Description

Usage: just create an instance of SimpleAsyncIO and then issue IO with pread and pwrite, no other effort required. e.g.:

auto tmpfile = folly::File::temporary(); folly::SimpleAsyncIO aio; aio.pwrite( tmpfile.fd(), "hello world", 11, // size 0, // offset []rc) { LOG(INFO) << "Write completed with rc " << rc; });

IO is dispatched in the context of the calling thread; it may block briefly to obtain a lock on shared resources, but will not block for IO completion. If the IO queue is full (see setMaxRequests(size_t) in Config), IO fails with ‐EBUSY.

IO is completed on the executor specified in the config (global CPU executor by default).

IO is completed by calling the callback function provided to pread/pwrite. The single parameter to the callback is either a negative errno or the number of bytes transferred.

There is a "hidden" EventBase which polls for IO completion and dispatches completion events to the executor. You may specify an existing EventBase in the config (and you are then responsible for making sure the EventBase instance outlives the SimpleAsyncIO instance). If you do not specify one, a ScopedEventBaseThread instance will be created.

Following structure defines the configuration of a SimpleAsyncIO instance, in case you need to override the (sensible) defaults.

Typical usage is something like:

SimpleAsyncIO io(SimpleAsyncIO::Config() .setMaxRequests(100) .setMode(SimpleAsyncIO::Mode::IOURING));