--- name: "sd_bus_call_method_async" section: "3" platform: "linux" package: "libsystemd-dev" version: "257.13-1~deb13u1" release: "Debian 13 (Trixie)" platforms: ["linux"] url: "https://new.carta.tech/sd_bus_call_method" --- # sd\_bus\_call\_method\_async(3) Initialize a bus message object and invoke the corresponding D-Bus method call Part of [sd\_bus\_call\_method(3)](/sd_bus_call_method/3.md). ## NAME sd\_bus\_call\_method, sd\_bus\_call\_methodv, sd\_bus\_call\_method\_async, sd\_bus\_call\_method\_asyncv - Initialize a bus message object and invoke the corresponding D-Bus method call ## SYNOPSIS ``` #include ``` **typedef int (\*sd\_bus\_message\_handler\_t)(sd\_bus\_message \****m***, void \****userdata***, sd\_bus\_error \****ret\_error***);** **int sd\_bus\_call\_method(sd\_bus \****bus***, const char \****destination***, const char \****path***, const char \****interface***, const char \****member***, sd\_bus\_error \****ret\_error***, sd\_bus\_message \*\****reply***, const char \****types***, ...);** **int sd\_bus\_call\_methodv(sd\_bus \****bus***, const char \****destination***, const char \****path***, const char \****interface***, const char \****member***, sd\_bus\_error \****ret\_error***, sd\_bus\_message \*\****reply***, const char \****types***, va\_list** *ap***);** **int sd\_bus\_call\_method\_async(sd\_bus \****bus***, sd\_bus\_slot \*\****slot***, const char \****destination***, const char \****path***, const char \****interface***, const char \****member***, sd\_bus\_message\_handler\_t** *callback***, void \****userdata***, const char \****types***, ...);** **int sd\_bus\_call\_method\_asyncv(sd\_bus \****bus***, sd\_bus\_slot \*\****slot***, const char \****destination***, const char \****path***, const char \****interface***, const char \****member***, sd\_bus\_message\_handler\_t** *callback***, void \****userdata***, const char \****types***, va\_list** *ap***);** ## DESCRIPTION **sd\_bus\_call\_method()** is a convenience function for initializing a bus message object and calling the corresponding D-Bus method. It combines the [**sd\_bus\_message\_new\_method\_call**(3)](/sd_bus_message_new_method_call/3.md), [**sd\_bus\_message\_append**(3)](/sd_bus_message_append/3.md) and [**sd\_bus\_call**(3)](/sd_bus_call/3.md) functions into a single function call. **sd\_bus\_call\_method\_async()** is a convenience function for initializing a bus message object and calling the corresponding D-Bus method asynchronously. It combines the [**sd\_bus\_message\_new\_method\_call**(3)](/sd_bus_message_new_method_call/3.md), [**sd\_bus\_message\_append**(3)](/sd_bus_message_append/3.md) and [**sd\_bus\_call\_async**(3)](/sd_bus_call_async/3.md) functions into a single function call. ## RETURN VALUE On success, these functions return a non-negative integer. On failure, they return a negative errno-style error code. ### Errors See the man pages of [**sd\_bus\_message\_new\_method\_call**(3)](/sd_bus_message_new_method_call/3.md), [**sd\_bus\_message\_append**(3)](/sd_bus_message_append/3.md), [**sd\_bus\_call**(3)](/sd_bus_call/3.md) and [**sd\_bus\_call\_async**(3)](/sd_bus_call_async/3.md) for a list of possible errors. ## NOTES Functions described here are available as a shared library, which can be compiled against and linked to with the **libsystemd** [**pkg-config**(1)](/pkg-config/1.md) file. The code described here uses [**getenv**(3)](/getenv/3.md), which is declared to be not multi-thread-safe. This means that the code calling the functions described here must not call [**setenv**(3)](/setenv/3.md) from a parallel thread. It is recommended to only do calls to **setenv()** from an early phase of the program when no other threads have been started. ## EXAMPLES **Example 1. Make a call to a D-Bus method that takes a single parameter** ``` /* SPDX-License-Identifier: MIT-0 */ /* This is equivalent to: * busctl call org.freedesktop.systemd1 /org/freedesktop/systemd1 \ * org.freedesktop.systemd1.Manager GetUnitByPID $$ * * Compile with 'cc print-unit-path-call-method.c -lsystemd' */ #include #include #include #include #include #define _cleanup_(f) __attribute__((cleanup(f))) #define DESTINATION "org.freedesktop.systemd1" #define PATH "/org/freedesktop/systemd1" #define INTERFACE "org.freedesktop.systemd1.Manager" #define MEMBER "GetUnitByPID" static int log_error(int error, const char *message) { fprintf(stderr, "%s: %s\n", message, strerror(-error)); return error; } int main(int argc, char **argv) { _cleanup_(sd_bus_flush_close_unrefp) sd_bus *bus = NULL; _cleanup_(sd_bus_error_free) sd_bus_error error = SD_BUS_ERROR_NULL; _cleanup_(sd_bus_message_unrefp) sd_bus_message *reply = NULL; int r; r = sd_bus_open_system(&bus); if (r < 0) return log_error(r, "Failed to acquire bus"); r = sd_bus_call_method(bus, DESTINATION, PATH, INTERFACE, MEMBER, &error, &reply, "u", (unsigned) getpid()); if (r < 0) return log_error(r, MEMBER " call failed"); const char *ans; r = sd_bus_message_read(reply, "o", &ans); if (r < 0) return log_error(r, "Failed to read reply"); printf("Unit path is \"%s\".\n", ans); return 0; } ``` This defines a minimally useful program that will open a connection to the bus, call a method, wait for the reply, and finally extract and print the answer. It does error handling and proper memory management. ## HISTORY **sd\_bus\_call\_method()**, and **sd\_bus\_call\_method\_async()** were added in version 221. **sd\_bus\_call\_methodv()**, **sd\_bus\_call\_method\_asyncv()** were added in version 246. ## SEE ALSO [**systemd**(1)](/systemd/1.md), [**sd-bus**(3)](/sd-bus/3.md), [**sd\_bus\_message\_new\_method\_call**(3)](/sd_bus_message_new_method_call/3.md), [**sd\_bus\_message\_append**(3)](/sd_bus_message_append/3.md), [**sd\_bus\_call**(3)](/sd_bus_call/3.md), [**sd\_bus\_set\_property**(3)](/sd_bus_set_property/3.md), [**sd\_bus\_emit\_signal**(3)](/sd_bus_emit_signal/3.md)