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Pure Java implementation of libzmq
package zmq;
import java.io.Closeable;
import java.io.IOException;
import java.nio.channels.SelectableChannel;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;
import zmq.pipe.YPipe;
import zmq.util.Errno;
public final class Mailbox implements Closeable
{
// The pipe to store actual commands.
private final YPipe cpipe;
// Signaler to pass signals from writer thread to reader thread.
private final Signaler signaler;
// There's only one thread receiving from the mailbox, but there
// is arbitrary number of threads sending. Given that ypipe requires
// synchronized access on both of its endpoints, we have to synchronize
// the sending side.
private final Lock sync;
// True if the underlying pipe is active, i.e. when we are allowed to
// read commands from it.
private boolean active;
// mailbox name, for better debugging
private final String name;
private final Errno errno;
public Mailbox(Ctx ctx, String name, int tid)
{
this.errno = ctx.errno();
cpipe = new YPipe<>(Config.COMMAND_PIPE_GRANULARITY.getValue());
sync = new ReentrantLock();
signaler = new Signaler(ctx, tid, errno);
// Get the pipe into passive state. That way, if the users starts by
// polling on the associated file descriptor it will get woken up when
// new command is posted.
Command cmd = cpipe.read();
assert (cmd == null);
active = false;
this.name = name;
}
public SelectableChannel getFd()
{
return signaler.getFd();
}
void send(final Command cmd)
{
boolean ok = false;
sync.lock();
try {
cpipe.write(cmd, false);
ok = cpipe.flush();
}
finally {
sync.unlock();
}
if (!ok) {
signaler.send();
}
}
public Command recv(long timeout)
{
Command cmd;
// Try to get the command straight away.
if (active) {
cmd = cpipe.read();
if (cmd != null) {
return cmd;
}
// If there are no more commands available, switch into passive state.
active = false;
}
// Wait for signal from the command sender.
boolean rc = signaler.waitEvent(timeout);
if (!rc) {
assert (errno.get() == ZError.EAGAIN || errno.get() == ZError.EINTR);
return null;
}
// Receive the signal.
signaler.recv();
// Switch into active state.
active = true;
// Get a command.
cmd = cpipe.read();
assert (cmd != null);
return cmd;
}
@Override
public void close() throws IOException
{
// TODO: Retrieve and deallocate commands inside the cpipe.
// Work around problem that other threads might still be in our
// send() method, by waiting on the mutex before disappearing.
sync.lock();
sync.unlock();
signaler.close();
}
@Override
public String toString()
{
return super.toString() + "[" + name + "]";
}
}
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