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NAME |SYNOPSIS |DESCRIPTION |RETURN VALUE |NOTES |HISTORY |SEE ALSO |NOTES |COLOPHON | |
SD_EVENT_NEW(3) sd_event_newSD_EVENT_NEW(3)sd_event_new, sd_event_default, sd_event_ref, sd_event_unref, sd_event_unrefp, sd_event_get_tid, sd_event - Acquire and release an event loop object
#include <systemd/sd-event.h>typedef struct sd_event sd_event;int sd_event_new(sd_event **event);int sd_event_default(sd_event **event);sd_event *sd_event_ref(sd_event *event);sd_event *sd_event_unref(sd_event *event);void sd_event_unrefp(sd_event **event);int sd_event_get_tid(sd_event *event, pid_t *ret);
sd_event_new()allocates a new event loop object. The event loop object is returned in theevent parameter. After use, drop the returned reference withsd_event_unref(). When the last reference is dropped, the object is freed.sd_event_default()acquires a reference to the default event loop object of the calling thread, possibly allocating a new object if no default event loop object has been allocated yet for the thread. After use, drop the returned reference withsd_event_unref(). When the last reference is dropped, the event loop is freed. If this function is called while the object returned from a previous call from the same thread is still referenced, the same object is returned again, but the reference is increased by one. It is recommended to use this call instead ofsd_event_new()in order to share event loop objects between various components that are dispatched in the same thread. All threads have exactly either zero or one default event loop objects associated, but never more. After allocating an event loop object, add event sources to it withsd_event_add_io(3),sd_event_add_time(3),sd_event_add_signal(3),sd_event_add_child(3),sd_event_add_inotify(3),sd_event_add_defer(3),sd_event_add_post(3) orsd_event_add_exit(3), and then execute the event loop usingsd_event_loop(3).sd_event_ref()increases the reference count of the specified event loop object by one.sd_event_unref()decreases the reference count of the specified event loop object by one. If the count hits zero, the object is freed. Note that it is freed regardless of whether it is the default event loop object for a thread or not. This means that allocating an event loop withsd_event_default(), then releasing it, and then acquiring a new one withsd_event_default()will result in two distinct objects. Note that, in order to free an event loop object, all remaining event sources of the event loop also need to be freed as each keeps a reference to it.sd_event_unrefp()is similar tosd_event_unref()but takes a pointer to a pointer to ansd_eventobject. This call is useful in conjunction with GCC's and LLVM'sClean-up Variable Attribute[1]. Note that this function is defined as inline function. Use a declaration like the following, in order to allocate an event loop object that is freed automatically as the code block is left: { __attribute__((cleanup(sd_event_unrefp))) sd_event *event = NULL; int r; ... r = sd_event_default(&event); if (r < 0) { errno = -r; fprintf(stderr, "Failed to allocate event loop: %m\n"); } ... }sd_event_ref(),sd_event_unref()andsd_event_unrefp()execute no operation if the passed in event loop object isNULL.sd_event_get_tid()retrieves the thread identifier ("TID") of the thread the specified event loop object is associated with. This call is only supported for event loops allocated withsd_event_default(), and returns the identifier for the thread the event loop is the default event loop of. Seegettid(2) for more information on thread identifiers.On success,sd_event_new(),sd_event_default()andsd_event_get_tid()return 0 or a positive integer. On failure, they return a negative errno-style error code.sd_event_ref() always returns a pointer to the event loop object passed in.sd_event_unref()always returnsNULL.Errors Returned errors may indicate the following problems:-ENOMEM Not enough memory to allocate the object.-EMFILE The maximum number of event loops has been allocated.-ENXIOsd_event_get_tid()was invoked on an event loop object that was not allocated withsd_event_default().
Functions described here are available as a shared library, which can be compiled against and linked to with thelibsystemd pkg-config(1) file. The code described here usesgetenv(3), which is declared to be not multi-thread-safe. This means that the code calling the functions described here must not callsetenv(3) from a parallel thread. It is recommended to only do calls tosetenv()from an early phase of the program when no other threads have been started.
sd_event_new(),sd_event_default(),sd_event_ref(), andsd_event_unref()were added in version 213.sd_event_unrefp()andsd_event_get_tid()were added in version 229.
systemd(1),sd-event(3),sd_event_add_io(3),sd_event_add_time(3),sd_event_add_signal(3),sd_event_add_child(3),sd_event_add_inotify(3),sd_event_add_defer(3),sd_event_run(3),gettid(2)
1. Clean-up Variable Attributehttps://gcc.gnu.org/onlinedocs/gcc/Common-Variable-Attributes.html
This page is part of thesystemd (systemd system and service manager) project. Information about the project can be found at ⟨http://www.freedesktop.org/wiki/Software/systemd⟩. If you have a bug report for this manual page, see ⟨http://www.freedesktop.org/wiki/Software/systemd/#bugreports⟩. This page was obtained from the project's upstream Git repository ⟨https://github.com/systemd/systemd.git⟩ on 2025-08-11. (At that time, the date of the most recent commit that was found in the repository was 2025-08-11.) If you discover any rendering problems in this HTML version of the page, or you believe there is a better or more up-to-date source for the page, or you have corrections or improvements to the information in this COLOPHON (which isnot part of the original manual page), send a mail to man-pages@man7.orgsystemd 258~rc2SD_EVENT_NEW(3)Pages that refer to this page:sd-event(3), sd_event_add_child(3), sd_event_add_defer(3), sd_event_add_inotify(3), sd_event_add_io(3), sd_event_add_memory_pressure(3), sd_event_add_signal(3), sd_event_add_time(3), sd_event_exit(3), sd_event_get_fd(3), sd_event_now(3), sd_event_run(3), sd_event_set_signal_exit(3), sd_event_set_watchdog(3), sd_event_wait(3), systemd.directives(7), systemd.index(7)
HTML rendering created 2025-09-06 byMichael Kerrisk, author ofThe Linux Programming Interface. For details of in-depthLinux/UNIX system programming training courses that I teach, lookhere. Hosting byjambit GmbH. | |