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

  ;;;
  ;;; 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.