// Copyright 2019 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
library zx;

@transport("Syscall")
closed protocol Eventpair {
    /// ## Summary
    ///
    /// Create an event pair.
    ///
    /// ## Declaration
    ///
    /// ```c
    /// #include <zircon/syscalls.h>
    ///
    /// zx_status_t zx_eventpair_create(uint32_t options,
    ///                                 zx_handle_t* out0,
    ///                                 zx_handle_t* out1);
    /// ```
    ///
    /// ## Description
    ///
    /// `zx_eventpair_create()` creates an event pair, which is a pair of objects that
    /// are mutually signalable.
    ///
    /// The signals `ZX_EVENTPAIR_SIGNALED` and `ZX_USER_SIGNAL_n` (where *n* is 0 through 7)
    /// may be set or cleared using [`zx_object_signal()`], which modifies the signals on the
    /// object itself, or [`zx_object_signal_peer()`], which modifies the signals on its
    /// counterpart.
    ///
    /// When all the handles to one of the objects have been closed, the
    /// `ZX_EVENTPAIR_PEER_CLOSED` signal will be asserted on the opposing object.
    ///
    /// The newly-created handles will have the `ZX_RIGHT_TRANSFER`,
    /// `ZX_RIGHT_DUPLICATE`, `ZX_RIGHT_READ`, `ZX_RIGHT_WRITE`, `ZX_RIGHT_SIGNAL`,
    /// and `ZX_RIGHT_SIGNAL_PEER` rights.
    ///
    /// Currently, no options are supported, so *options* must be set to 0.
    ///
    /// ## Rights
    ///
    /// Caller job policy must allow `ZX_POL_NEW_EVENTPAIR`.
    ///
    /// ## Return value
    ///
    /// `zx_eventpair_create()` returns `ZX_OK` on success. On failure, a (negative)
    /// error code is returned.
    ///
    /// ## Errors
    ///
    /// `ZX_ERR_INVALID_ARGS`  *out0* or *out1* is an invalid pointer or NULL.
    ///
    /// `ZX_ERR_NOT_SUPPORTED`  *options* has an unsupported flag set (i.e., is not 0).
    ///
    /// `ZX_ERR_NO_MEMORY`  Failure due to lack of memory.
    /// There is no good way for userspace to handle this (unlikely) error.
    /// In a future build this error will no longer occur.
    ///
    /// ## See also
    ///
    ///  - [`zx_event_create()`]
    ///  - [`zx_handle_close()`]
    ///  - [`zx_handle_duplicate()`]
    ///  - [`zx_handle_replace()`]
    ///  - [`zx_object_signal()`]
    ///  - [`zx_object_signal_peer()`]
    ///  - [`zx_object_wait_async()`]
    ///  - [`zx_object_wait_many()`]
    ///  - [`zx_object_wait_one()`]
    ///
    /// [`zx_event_create()`]: event_create.md
    /// [`zx_handle_close()`]: handle_close.md
    /// [`zx_handle_duplicate()`]: handle_duplicate.md
    /// [`zx_handle_replace()`]: handle_replace.md
    /// [`zx_object_signal()`]: object_signal.md
    /// [`zx_object_signal_peer()`]: object_signal_peer.md
    /// [`zx_object_wait_async()`]: object_wait_async.md
    /// [`zx_object_wait_many()`]: object_wait_many.md
    /// [`zx_object_wait_one()`]: object_wait_one.md
    strict Create(struct {
        options uint32;
    }) -> (resource struct {
        out0 Handle:EVENT;
        out1 Handle:EVENT;
    }) error Status;
};