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//
// Copyright 2017 Garrett D'Amore <garrett@damore.org>
//
// This software is supplied under the terms of the MIT License, a
// copy of which should be located in the distribution where this
// file was obtained (LICENSE.txt). A copy of the license may also be
// found online at https://opensource.org/licenses/MIT.
//
#ifndef CORE_MSGQUEUE_H
#define CORE_MSGQUEUE_H
#include "nng_impl.h"
// Message queues. Message queues work in some ways like Go channels;
// they are a thread-safe way to pass messages between subsystems. They
// do have additional capabilities though.
//
// A closed message queue cannot be written to, but if there are messages
// still in it and it is draining, it can be read from. This permits
// linger operations to work.
//
// Message queues can be closed many times safely.
//
// Readers & writers in a message queue can be woken either by a timeout
// or by a specific signal (arranged by the caller).
typedef struct nni_msgq nni_msgq;
// nni_msgq_init creates a message queue with the given capacity,
// which must be a positive number. It returns NNG_EINVAL if the capacity
// is invalid, or NNG_ENOMEM if resources cannot be allocated.
extern int nni_msgq_init(nni_msgq **, int);
// nni_msgq_fini destroys a message queue. It will also free any
// messages that may be in the queue.
extern void nni_msgq_fini(nni_msgq *);
// nni_msgq_put puts the message to the queue. It blocks until it
// was able to do so, or the queue is closed, returning either 0 on
// success or NNG_ECLOSED if the queue was closed. If NNG_ECLOSED is
// returned, the caller is responsible for freeing the message with
// nni_msg_free(), otherwise the message is "owned" by the queue, and
// the caller is not permitted to access it further.
extern int nni_msgq_put(nni_msgq *, nni_msg *);
// nni_msgq_tryput is like nni_msgq_put, except that it does not block,
// if there is no room to put the message it simply returns NNG_EAGAIN.
extern int nni_msgq_tryput(nni_msgq *, nni_msg *);
// nni_msgq_putback returns a message to the head of the queue.
// This is a non-blocking operation, and it returns NNG_EAGAIN if there
// is no room. There is always at least room for one putback after
// a message is retried with nni_msgq_get.
extern int nni_msgq_putback(nni_msgq *, nni_msg *);
// nni_msgq_get gets the message from the queue. It blocks until a
// message is available, or the queue is closed, returning either 0 on
// success or NNG_ECLOSED if the queue was closed. If a message is
// provided, the caller is assumes ownership of the message and must
// call nni_msg_free() when it is finished with it.
extern int nni_msgq_get(nni_msgq *, nni_msg **);
// nni_msgq_put_until is like nni_msgq_put, except that if the
// system clock reaches the specified time without being able to place
// the message in the queue, it will return NNG_ETIMEDOUT.
extern int nni_msgq_put_until(nni_msgq *, nni_msg *, nni_time);
// nni_msgq_get_until is like nni_msgq_put, except that if the
// system clock reaches the specified time without being able to retrieve
// a message from the queue, it will return NNG_ETIMEDOUT.
extern int nni_msgq_get_until(nni_msgq *, nni_msg **, nni_time);
// nni_msgq_put_sig is an enhanced version of nni_msgq_put, but it
// can be interrupted by nni_msgqueue_signal using the same final pointer,
// which can be thought of as a turnstile. If interrupted it returns EINTR.
// The turnstile should be initialized to zero.
extern int nni_msgq_put_sig(nni_msgq *, nni_msg *, nni_signal *);
// nni_msgq_get_sig is an enhanced version of nni_msgq_get_t, but it
// can be interrupted by nni_msgq_signal using the same final pointer,
// which can be thought of as a turnstile. If interrupted it returns EINTR.
// The turnstile should be initialized to zero.
extern int nni_msgq_get_sig(nni_msgq *, nni_msg **, nni_signal *);
// nni_msgq_signal delivers a signal / interrupt to waiters blocked in
// the msgq, if they have registered an interest in the same turnstile.
// It modifies the turnstile's value under the lock to a non-zero value.
extern void nni_msgq_signal(nni_msgq *, nni_signal *);
// nni_msgq_close closes the queue. After this all operates on the
// message queue will return NNG_ECLOSED. Messages inside the queue
// are freed. Unlike closing a go channel, this operation is idempotent.
extern void nni_msgq_close(nni_msgq *);
// nni_msgq_drain is like nng_msgq_close, except that reads
// against the queue are permitted for up to the time limit. The
// operation blocks until either the queue is empty, or the timeout
// has expired. Any messages still in the queue at the timeout are freed.
extern void nni_msgq_drain(nni_msgq *, nni_time);
// nni_msgq_resize resizes the message queue; messages already in the queue
// will be preserved as long as there is room. Messages that are dropped
// due to no room are taken from the most recent. (Oldest messages are
// preserved.)
extern int nni_msgq_resize(nni_msgq *, int);
// nni_msgq_cap returns the "capacity" of the message queue. This does not
// include the extra room for pushback, nor the extra slot reserved to make
// zero-length message queues possible. As a consequence, it is possible
// for the message queue to contain up to 2 more messages than the capacity.
extern int nni_msgq_cap(nni_msgq *mq);
// nni_msgq_len returns the number of messages currently in the queue.
extern int nni_msgq_len(nni_msgq *mq);
#endif // CORE_MSQUEUE_H
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