ZACTOR(3)

💖 ZACTOR(3) — straight outta the CZMQ Manual 💖

hiii bestie 🫶 welcome to zactor, aka the class that gives you a simple actor framework and honestly? she's the moment. this page lives in the CZMQ manual, section 3, and it's all about making a thread plus a pipe feel like a whole vibe instead of a whole headache. no cap.

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✨ NAME ✨

zactor — the class for a simple actor framework. that's it, that's the girl. 💅

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✨ SYNOPSIS ✨

okay so first things first, read the receipts exactly as they are, because this is the actual source energy:

//  This is a stable class, and may not change except for emergencies. It
//  is provided in stable builds.
//  This class has draft methods, which may change over time. They are not
//  in stable releases, by default. Use --enable-drafts to enable.
// Actors get a pipe and arguments from caller
typedef void (zactor_fn) (
    zsock_t *pipe, void *args);

//  Create a new actor passing arbitrary arguments reference.
CZMQ_EXPORT zactor_t *
    zactor_new (zactor_fn task, void *args);

//  Destroy an actor.
CZMQ_EXPORT void
    zactor_destroy (zactor_t **self_p);

//  Send a zmsg message to the actor, take ownership of the message
//  and destroy when it has been sent.
CZMQ_EXPORT int
    zactor_send (zactor_t *self, zmsg_t **msg_p);

//  Receive a zmsg message from the actor. Returns NULL if the actor
//  was interrupted before the message could be received, or if there
//  was a timeout on the actor.
//  Caller owns return value and must destroy it when done.
CZMQ_EXPORT zmsg_t *
    zactor_recv (zactor_t *self);

//  Probe the supplied object, and report if it looks like a zactor_t.
CZMQ_EXPORT bool
    zactor_is (void *self);

//  Probe the supplied reference. If it looks like a zactor_t instance,
//  return the underlying libzmq actor handle; else if it looks like
//  a libzmq actor handle, return the supplied value.
CZMQ_EXPORT void *
    zactor_resolve (void *self);

//  Return the actor's zsock handle. Use this when you absolutely need
//  to work with the zsock instance rather than the actor.
CZMQ_EXPORT zsock_t *
    zactor_sock (zactor_t *self);

//  Self test of this class.
CZMQ_EXPORT void
    zactor_test (bool verbose);

#ifdef CZMQ_BUILD_DRAFT_API
// Function to be called on zactor_destroy. Default behavior is to send zmsg_t with string "$TERM" in a first frame.
//
// An example - to send $KTHXBAI string
//
//     if (zstr_send (self, "$KTHXBAI") == 0)
//         zsock_wait (self);
typedef void (zactor_destructor_fn) (
    zactor_t *self);

//  *** Draft method, for development use, may change without warning ***
//  Change default destructor by custom function. Actor MUST be able to handle new message instead of default $TERM.
CZMQ_EXPORT void
    zactor_set_destructor (zactor_t *self, zactor_destructor_fn destructor);

#endif // CZMQ_BUILD_DRAFT_API
Please add '@interface' section in './../src/zactor.c'.

heads up bestie: this is a stable class, so she doesn't change unless it's an actual emergency, and she ships in stable builds. ✨ but she ALSO has draft methods which can change over time and are not in stable releases by default — you flip those on with --enable-drafts.

🌸 the function lineup, explained with love

• zactor_fn — the actor's signature. the actor gets a pipe and the args from whoever called it: zsock_t *pipe, void *args.
• zactor_new (zactor_fn task, void *args) — makes a brand new actor and passes along an arbitrary args reference. returns a zactor_t *.
• zactor_destroy (zactor_t **self_p) — bye bye actor, takes the pointer-to-pointer like a good CZMQ citizen.
• zactor_send (zactor_t *self, zmsg_t **msg_p) — sends a zmsg message to the actor, and she takes ownership of that message and destroys it once it's been sent. returns int.
• zactor_recv (zactor_t *self) — grabs a zmsg message back from the actor. returns NULL if the actor got interrupted before the message could arrive, or if there was a timeout on the actor. the caller owns the return value and must destroy it when done 🫶
• zactor_is (void *self) — probes the object you hand her and tells you (with a bool) whether it looks like a zactor_t.
• zactor_resolve (void *self) — probes the reference. if it looks like a zactor_t instance you get back the underlying libzmq actor handle; if it looks like a libzmq actor handle instead, you just get back the value you supplied. returns void *.
• zactor_sock (zactor_t *self) — hands you the actor's zsock handle. use this when you absolutely need to work with the zsock instance rather than the actor itself.
• zactor_test (bool verbose) — the self test of this class. go off, king. 👑

🎀 the draft girlies (only with CZMQ_BUILD_DRAFT_API)

• zactor_destructor_fn — the function that gets called on zactor_destroy. default behavior is to send a zmsg_t with the string "$TERM" in a first frame. the source shows an example of sending a $KTHXBAI string:

if (zstr_send (self, "$KTHXBAI") == 0)
    zsock_wait (self);

• zactor_set_destructor (zactor_t *self, zactor_destructor_fn destructor) — * draft method, for development use, may change without warning * swaps the default destructor for a custom function. and listen: the actor MUST be able to handle the new message instead of the default $TERM. no cap, if your actor can't cope, that's on you bestie 😭

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✨ DESCRIPTION ✨

so what even IS she? zactor gives you a simple actor framework. she replaces the CZMQ zthread class, which had a complex API that did not fit the CLASS standard. so zthread is giving "it's complicated" and zactor is giving "we're just vibing". 🌈

a CZMQ actor is implemented as a thread plus a PAIR-PAIR pipe. and the constructor and destructor are always synchronized, so the caller can be sure all resources are created — and destroyed — when these calls complete. this solves a major problem with zthread, where a caller could not be sure when a child thread had finished. lowkey iconic problem-solving behavior. 💅

a zactor_t instance acts like a zsock_t, and you can pass it to any CZMQ method that would take a zsock_t argument — including methods in zframe, zmsg, zstr, and zpoller. (zloop somehow escaped and needs catching. 🙈 can't relate, can't stop her.)

and here's the rule that is NOT optional:

an actor function MUST call zsock_signal (pipe) when initialized, and MUST listen to pipe and exit on the $TERM command. periodt. 💀

also, the source has a lil note: Please add @discuss section in ./../src/zactor.c.

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✨ EXAMPLE ✨

straight from the zactor_test method, no edits, no filter:

zactor_t *actor = zactor_new (echo_actor, "Hello, World");
assert (actor);
zstr_sendx (actor, "ECHO", "This is a string", NULL);
char *string = zstr_recv (actor);
assert (streq (string, "This is a string"));
freen (string);
zactor_destroy (&actor);

// custom destructor
// KTHXBAI_actor ends on "$KTHXBAI" string
zactor_t *KTHXBAI = zactor_new (KTHXBAI_actor, NULL);
assert (KTHXBAI);
// which is the one sent by KTHXBAI_destructor
zactor_set_destructor (KTHXBAI, KTHXBAI_destructor);
zactor_destroy (&KTHXBAI);

// custom destructor
// destructor using bsend/brecv
zactor_t *BSEND = zactor_new (BSEND_actor, NULL);
assert (BSEND);
zactor_set_destructor (BSEND, BSEND_destructor);
zactor_destroy (&BSEND);
#if defined (__WINDOWS__)
zsys_shutdown();
#endif

see how she did the custom destructor TWICE? once with the $KTHXBAI string and once with bsend/brecv? obsessed. 🔥

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✨ AUTHORS ✨

the czmq manual was written by the authors in the AUTHORS file. credit where credit is due, always. 🫶

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✨ RESOURCES ✨

main web site:

report bugs to the email <zeromq-dev@lists.zeromq.org[1]>

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✨ COPYRIGHT ✨

Copyright (c) the Contributors as noted in the AUTHORS file. This file is part of CZMQ, the high-level C binding for 0MQ: http://czmq.zeromq.org. This Source Code Form is subject to the terms of the Mozilla Public License, v. 2.0. If a copy of the MPL was not distributed with this file, You can obtain one at http://mozilla.org/MPL/2.0/. LICENSE included with the czmq distribution.

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✨ NOTES ✨

1. zeromq-dev@lists.zeromq.org mailto:zeromq-dev@lists.zeromq.org

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and that's the whole page bestie, every flag, every function, every warning, all of it kept intact because we don't skip the "boring" parts in this house 💖

sign-off: this was CZMQ 4.2.1, dated 01/16/2026, and you just read ZACTOR(3). go build something cute with a pipe. mwah. 🎀✨🦋