# sd_event_new

## NAME



           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
    


## SYNOPSIS



           **#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_**);**
    


## DESCRIPTION



           **sd_event_new()** allocates a new event loop object. The event loop
           object is returned in the _event_ parameter. After use, drop the
           returned reference with **sd_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 with
           **sd_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 of
           **sd_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
           with 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_add_post(3) or sd_event_add_exit(3), and then execute the
           event loop using sd_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 with **sd_event_default()** , then releasing
           it, and then acquiring a new one with **sd_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 to **sd_event_unref()** but takes a
           pointer to a pointer to an **sd_event** object. This call is useful in
           conjunction with GCC's and LLVM's **Clean-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()** and **sd_event_unrefp()** execute no
           operation if the passed in event loop object is **NULL**.
    
           **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 with
           **sd_event_default()** , and returns the identifier for the thread the
           event loop is the default event loop of. See gettid(2) for more
           information on thread identifiers.
    


## RETURN VALUE



           On success, **sd_event_new()** , **sd_event_default()** and
           **sd_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 returns **NULL**.
    
       **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.
    
           **-ENXIO**
               **sd_event_get_tid()** was invoked on an event loop object that
               was not allocated with **sd_event_default()**.
    


## NOTES



           Functions described here are available as a shared library, which
           can be compiled against and linked to with the
           **libsystemd pkg-config**(1) file.
    
           The code described here uses getenv(3), which is declared to be
           not multi-thread-safe. This means that the code calling the
           functions described here must not call setenv(3) 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.
    


## NOTES



            1. Clean-up Variable Attribute
               https://gcc.gnu.org/onlinedocs/gcc/Common-Variable-Attributes.html
    


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