1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
//! Tokio context aware futures utilities.
//!
//! This module includes utilities around integrating tokio with other runtimes
//! by allowing the context to be attached to futures. This allows spawning
//! futures on other executors while still using tokio to drive them. This
//! can be useful if you need to use a tokio based library in an executor/runtime
//! that does not provide a tokio context.

use pin_project_lite::pin_project;
use std::{
    future::Future,
    pin::Pin,
    task::{Context, Poll},
};
use tokio::runtime::{Handle, Runtime};

pin_project! {
    /// `TokioContext` allows running futures that must be inside Tokio's
    /// context on a non-Tokio runtime.
    ///
    /// It contains a [`Handle`] to the runtime. A handle to the runtime can be
    /// obtain by calling the [`Runtime::handle()`] method.
    ///
    /// Note that the `TokioContext` wrapper only works if the `Runtime` it is
    /// connected to has not yet been destroyed. You must keep the `Runtime`
    /// alive until the future has finished executing.
    ///
    /// **Warning:** If `TokioContext` is used together with a [current thread]
    /// runtime, that runtime must be inside a call to `block_on` for the
    /// wrapped future to work. For this reason, it is recommended to use a
    /// [multi thread] runtime, even if you configure it to only spawn one
    /// worker thread.
    ///
    /// # Examples
    ///
    /// This example creates two runtimes, but only [enables time] on one of
    /// them. It then uses the context of the runtime with the timer enabled to
    /// execute a [`sleep`] future on the runtime with timing disabled.
    /// ```
    /// use tokio::time::{sleep, Duration};
    /// use tokio_util::context::RuntimeExt;
    ///
    /// // This runtime has timers enabled.
    /// let rt = tokio::runtime::Builder::new_multi_thread()
    ///     .enable_all()
    ///     .build()
    ///     .unwrap();
    ///
    /// // This runtime has timers disabled.
    /// let rt2 = tokio::runtime::Builder::new_multi_thread()
    ///     .build()
    ///     .unwrap();
    ///
    /// // Wrap the sleep future in the context of rt.
    /// let fut = rt.wrap(async { sleep(Duration::from_millis(2)).await });
    ///
    /// // Execute the future on rt2.
    /// rt2.block_on(fut);
    /// ```
    ///
    /// [`Handle`]: struct@tokio::runtime::Handle
    /// [`Runtime::handle()`]: fn@tokio::runtime::Runtime::handle
    /// [`RuntimeExt`]: trait@crate::context::RuntimeExt
    /// [`new_static`]: fn@Self::new_static
    /// [`sleep`]: fn@tokio::time::sleep
    /// [current thread]: fn@tokio::runtime::Builder::new_current_thread
    /// [enables time]: fn@tokio::runtime::Builder::enable_time
    /// [multi thread]: fn@tokio::runtime::Builder::new_multi_thread
    pub struct TokioContext<F> {
        #[pin]
        inner: F,
        handle: Handle,
    }
}

impl<F> TokioContext<F> {
    /// Associate the provided future with the context of the runtime behind
    /// the provided `Handle`.
    ///
    /// This constructor uses a `'static` lifetime to opt-out of checking that
    /// the runtime still exists.
    ///
    /// # Examples
    ///
    /// This is the same as the example above, but uses the `new` constructor
    /// rather than [`RuntimeExt::wrap`].
    ///
    /// [`RuntimeExt::wrap`]: fn@RuntimeExt::wrap
    ///
    /// ```
    /// use tokio::time::{sleep, Duration};
    /// use tokio_util::context::TokioContext;
    ///
    /// // This runtime has timers enabled.
    /// let rt = tokio::runtime::Builder::new_multi_thread()
    ///     .enable_all()
    ///     .build()
    ///     .unwrap();
    ///
    /// // This runtime has timers disabled.
    /// let rt2 = tokio::runtime::Builder::new_multi_thread()
    ///     .build()
    ///     .unwrap();
    ///
    /// let fut = TokioContext::new(
    ///     async { sleep(Duration::from_millis(2)).await },
    ///     rt.handle().clone(),
    /// );
    ///
    /// // Execute the future on rt2.
    /// rt2.block_on(fut);
    /// ```
    pub fn new(future: F, handle: Handle) -> TokioContext<F> {
        TokioContext {
            inner: future,
            handle,
        }
    }

    /// Obtain a reference to the handle inside this `TokioContext`.
    pub fn handle(&self) -> &Handle {
        &self.handle
    }

    /// Remove the association between the Tokio runtime and the wrapped future.
    pub fn into_inner(self) -> F {
        self.inner
    }
}

impl<F: Future> Future for TokioContext<F> {
    type Output = F::Output;

    fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
        let me = self.project();
        let handle = me.handle;
        let fut = me.inner;

        let _enter = handle.enter();
        fut.poll(cx)
    }
}

/// Extension trait that simplifies bundling a `Handle` with a `Future`.
pub trait RuntimeExt {
    /// Create a [`TokioContext`] that wraps the provided future and runs it in
    /// this runtime's context.
    ///
    /// # Examples
    ///
    /// This example creates two runtimes, but only [enables time] on one of
    /// them. It then uses the context of the runtime with the timer enabled to
    /// execute a [`sleep`] future on the runtime with timing disabled.
    ///
    /// ```
    /// use tokio::time::{sleep, Duration};
    /// use tokio_util::context::RuntimeExt;
    ///
    /// // This runtime has timers enabled.
    /// let rt = tokio::runtime::Builder::new_multi_thread()
    ///     .enable_all()
    ///     .build()
    ///     .unwrap();
    ///
    /// // This runtime has timers disabled.
    /// let rt2 = tokio::runtime::Builder::new_multi_thread()
    ///     .build()
    ///     .unwrap();
    ///
    /// // Wrap the sleep future in the context of rt.
    /// let fut = rt.wrap(async { sleep(Duration::from_millis(2)).await });
    ///
    /// // Execute the future on rt2.
    /// rt2.block_on(fut);
    /// ```
    ///
    /// [`TokioContext`]: struct@crate::context::TokioContext
    /// [`sleep`]: fn@tokio::time::sleep
    /// [enables time]: fn@tokio::runtime::Builder::enable_time
    fn wrap<F: Future>(&self, fut: F) -> TokioContext<F>;
}

impl RuntimeExt for Runtime {
    fn wrap<F: Future>(&self, fut: F) -> TokioContext<F> {
        TokioContext {
            inner: fut,
            handle: self.handle().clone(),
        }
    }
}