TEST(AsyncFileWriter, flush) {
// Set up a pipe(), then write data to the write endpoint until it fills up
// and starts blocking.
std::array<int, 2> fds;
auto rc = pipe(fds.data());
folly::checkUnixError(rc, "failed to create pipe");
File readPipe{fds[0], true};
File writePipe{fds[1], true};
auto paddingSize = fillUpPipe(writePipe.fd());
// Now set up an AsyncFileWriter pointing at the write end of the pipe
AsyncFileWriter writer{std::move(writePipe)};
// Write a message
writer.writeMessage("test message: " + std::string(200, 'x'));
// Call flush(). Use a separate thread, since this should block until we
// consume data from the pipe.
Promise<Unit> promise;
auto future = promise.getFuture();
auto flushFunction = [&] { writer.flush(); };
std::thread flushThread{
[&]() { promise.setTry(makeTryWith(flushFunction)); }};
// Detach the flush thread now rather than joining it at the end of the
// function. This way if something goes wrong during the test we will fail
// with the real error, rather than crashing due to the std::thread
// destructor running on a still-joinable thread.
flushThread.detach();
// Sleep briefly, and make sure flush() still hasn't completed.
// If it has completed this doesn't necessarily indicate a bug in
// AsyncFileWriter, but instead indicates that our test code failed to
// successfully cause a blocking write.
/* sleep override */
std::this_thread::sleep_for(10ms);
EXPECT_FALSE(future.isReady());
// Now read from the pipe
std::vector<char> buf;
buf.resize(paddingSize);
readFull(readPipe.fd(), buf.data(), buf.size());
// Make sure flush completes successfully now
future.get(10ms);
}