---
title: "fd_event()"
description: "Creates a file handle for event notifications."
url: "https://wasix.org/docs/api-reference/wasix/fd_event/"
markdown: "https://wasix.org/docs/api-reference/wasix/fd_event.md"
---

# `fd_event()`

Creates a file handle for event notifications.

## Description

The `fd_event()` function creates a file handle that can be used for event notifications. Event notifications allow synchronization and communication between different parts of an application.

## Syntax

```ebnf
  ;;;
  ;;; Creates a file handle for event notifications
  (@interface func (export "fd_event")
    (param $initial_val u64)
    (param $flags $eventfdflags)
    (result $error (expected $fd (error $errno)))
  )
```

## Parameters

- `ctx`: A mutable reference to the function environment.
- `initial_val`: The initial value for the event.
- `flags`: Flags for the event file handle.
- `ret_fd`: A WebAssembly memory pointer where the new file handle will be stored.

## Return Value

The function returns an `Errno` value indicating the success or failure of the operation.

## Logging

This function has been instrumented with debug-level logging. It will log the following information:

- `%initial_val`: The initial value for the event.
- `ret_fd`: The file handle created for the event.

## Note

The `fd_event()` function creates a file handle for event notifications. It takes the initial value for the event, flags for the event file handle, and a WebAssembly memory pointer `ret_fd` where the new file handle will be stored.

The function retrieves the memory view, file system state, and inodes from the WASI environment using the function context.

The function determines whether the event is a semaphore event based on the `EVENT_FD_FLAGS_SEMAPHORE` flag in the `flags` parameter.

It creates an `EventNotifications` kind with an `Arc` wrapping a `NotificationInner` that holds the event state. The `NotificationInner` is initialized with the provided `initial_val` and the `is_semaphore` flag.

The `EventNotifications` kind is then used to create an inode using the `create_inode_with_default_stat()` method of the file system state. The `create_inode_with_default_stat()` method generates a default stat structure for the inode.

Next, the function creates a file descriptor (`fd`) using the `create_fd()` method of the file system state. The file descriptor is created with the specified rights, flags, and inode.

The created file handle is stored in the WebAssembly memory using the provided memory pointer `ret_fd`.

The function returns an `Errno` value to indicate the success or failure of the operation. If the file handle for event notifications is successfully created, it returns `Errno::Success`. Otherwise, it returns an appropriate error code.

---

[Documentation index](https://wasix.org/llms.txt) · [HTML version](https://wasix.org/docs/api-reference/wasix/fd_event/)