redis_lock/
lib.rs

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
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
#![cfg_attr(docsrs, feature(doc_cfg))]

//! Rusty distributed locking backed by Redis.
//!
//! ## Locking a single resource
//!
//! ```no_run
//! # use redis::AsyncCommands;
//! # use tokio::sync::Mutex;
//! # use std::sync::Arc;
//! # #[allow(dependency_on_unit_never_type_fallback)]
//! # fn main() -> Result<(), Box<dyn std::error::Error>> {
//! # tokio::runtime::Runtime::new()?.block_on(async {
//! # let client: redis::Client = todo!();
//! let connection = Arc::new(Mutex::new(
//!     client.get_multiplexed_async_connection().await?
//! ));
//! // Execute a function with the lock.
//! redis_lock::lock_across(
//!     &[connection],
//!     "account1",
//!     async move { /* .. */ },
//!     redis_lock::LockAcrossOptions::default()
//! ).await?;
//! # Ok(())
//! # })
//! # }
//! ```
//!
//! ## Locking multiple resources
//!
//! ```no_run
//! # use redis::AsyncCommands;
//! # #[allow(dependency_on_unit_never_type_fallback)]
//! # fn main() -> Result<(), Box<dyn std::error::Error>> {
//! # tokio::runtime::Runtime::new()?.block_on(async {
//! # let client = todo!();
//! // Setup.
//! redis_lock::setup(&client).await?;
//! // Get lock.
//! let mut lock = redis_lock::MultiResourceLock::new(client.clone())?;
//! let resources = vec![String::from("account1"), String::from("account2")];
//! // Execute a function with the lock.
//! lock.map_default(&resources, async move { /* .. */ }).await?;
//! # Ok(())
//! # })
//! # }
//! ```
//!
//! ## Vs [rslock](https://github.com/hexcowboy/rslock)
//!
//! I would recommend this library over [rslock](https://github.com/hexcowboy/rslock) when:
//! - your application is focussed on `async`.
//! - your application does operations that require exclusive access to multiple resources.
//!
//! ## Similar work
//!
//! - <https://github.com/hexcowboy/rslock>

use displaydoc::Display;
use redis::Client;
use std::error::Error;
use std::future::Future;
use std::time::Duration;
use thiserror::Error;
use uuid::Uuid;

/// Re-export of [`redis::RedisError`].
pub type RedisError = redis::RedisError;
/// Mimic of [`redis::RedisResult`].
pub type RedisResult<T> = Result<T, RedisError>;

/// Synchronous implementation of the lock.
#[cfg(feature = "sync")]
#[cfg_attr(docsrs, doc(cfg(feature = "sync")))]
pub mod sync;

mod single;
pub use single::*;

/// A distributed mutual exclusion lock backed by Redis.
///
/// Supports exclusion based on multiple resources and partial overlaps.
///
/// This is much less efficient than [`lock_across`]. Ideally you should architect your
/// application so you never need [`MultiResourceLock`].
///
/// E.g. a lock on resources `["a", "b"]` will block a lock on `["a"]` or `["b", "c"]`.
pub struct MultiResourceLock {
    /// The Redis client.
    client: Client,
}

impl std::fmt::Debug for MultiResourceLock {
    #[inline]
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        f.debug_struct("MultiResourceLock")
            .field("conn", &"..")
            .finish()
    }
}

/// Initializes a Redis instance with the Lua library functions required for locking.
///
/// This only needs to be done once per Redis instance, although re-doing it should be fine.
///
/// # Errors
///
/// - When [`Client::get_connection`] errors.
/// - When the Lua library functions cannot be loaded into Redis.
#[inline]
pub async fn setup(client: &Client) -> Result<(), Box<dyn Error>> {
    // Connect to Redis
    let mut con = client.get_multiplexed_async_connection().await?;

    // Define your Lua library
    let lua_library = include_str!("functions.lua");

    // Load the Lua library into Redis
    redis::cmd("FUNCTION")
        .arg("LOAD")
        .arg("REPLACE")
        .arg(lua_library)
        .exec_async(&mut con)
        .await?;

    Ok(())
}

/// Default expiration duration for the lock.
pub const DEFAULT_EXPIRATION: Duration = Duration::from_secs(3600);
/// Default timeout duration for acquiring the lock.
pub const DEFAULT_TIMEOUT: Duration = Duration::from_secs(60);
/// Default sleep duration between attempts to acquire the lock.
pub const DEFAULT_SLEEP: Duration = Duration::from_secs(1);

impl MultiResourceLock {
    /// Create a new instance of the lock.
    ///
    /// # Errors
    ///
    /// When [`Client::get_connection`] errors.
    #[inline]
    pub fn new(client: Client) -> RedisResult<Self> {
        Ok(MultiResourceLock { client })
    }

    /// Calls [`MultiResourceLock::acquire`] with [`DEFAULT_EXPIRATION`], [`DEFAULT_TIMEOUT`] and [`DEFAULT_SLEEP`].
    ///
    /// # Errors
    ///
    /// When [`MultiResourceLock::acquire`] errors.
    #[inline]
    pub async fn acquire_default(&mut self, resources: &[String]) -> RedisResult<Option<String>> {
        self.acquire(
            resources,
            DEFAULT_EXPIRATION,
            DEFAULT_TIMEOUT,
            DEFAULT_SLEEP,
        )
        .await
    }

    /// Attempts to acquire the lock blocking until the lock can be acquired.
    ///
    /// Blocks up to `timeout` duration making attempts every `sleep` duration.
    ///
    /// Returns `None` when it times out.
    ///
    /// # Errors
    ///
    /// When [`MultiResourceLock::try_acquire`] errors.
    #[inline]
    pub async fn acquire(
        &mut self,
        resources: &[String],
        expiration: Duration,
        timeout: Duration,
        sleep: Duration,
    ) -> RedisResult<Option<String>> {
        let now = std::time::Instant::now();
        loop {
            if now.elapsed() > timeout {
                return Ok(None);
            }
            match self.try_acquire(resources, expiration).await? {
                Some(res) => break Ok(Some(res)),
                None => tokio::time::sleep(sleep).await,
            }
        }
    }

    /// Calls [`MultiResourceLock::try_acquire`] with [`DEFAULT_EXPIRATION`].
    ///
    /// # Errors
    ///
    /// When [`MultiResourceLock::try_acquire`] errors.
    #[inline]
    pub async fn try_acquire_default(
        &mut self,
        resources: &[String],
    ) -> RedisResult<Option<String>> {
        self.try_acquire(resources, DEFAULT_EXPIRATION).await
    }

    /// Attempts to acquire the lock returning immediately if it cannot be immediately acquired.
    ///
    /// # Errors
    ///
    /// - When the `acquire_lock` function is missing from the Redis instance.
    #[inline]
    pub async fn try_acquire(
        &mut self,
        resources: &[String],
        expiration: Duration,
    ) -> RedisResult<Option<String>> {
        let mut connection = self.client.get_multiplexed_async_connection().await?;
        let lock_id = Uuid::new_v4().to_string();
        let mut args = vec![lock_id.clone(), expiration.as_millis().to_string()];
        args.extend(resources.iter().cloned());

        let result: Option<String> = redis::cmd("FCALL")
            .arg("acquire_lock")
            .arg(0i32)
            .arg(&args)
            .query_async(&mut connection)
            .await?;

        Ok(result)
    }

    /// Releases a held lock.
    ///
    /// # Errors
    ///
    /// - When the `release_lock` function is missing from the Redis instance.
    /// - When `lock_id` does not refer to a held lock.
    #[inline]
    pub async fn release(&mut self, lock_id: &str) -> RedisResult<usize> {
        let mut connection = self.client.get_multiplexed_async_connection().await?;
        let result: usize = redis::cmd("FCALL")
            .arg("release_lock")
            .arg(0i32)
            .arg(lock_id)
            .query_async(&mut connection)
            .await?;

        Ok(result)
    }

    // TODO Catch panics in `f`.
    /// Since we cannot safely drop a guard in an async context, we need to provide a way to release the lock in case of an error.
    ///
    /// This is the suggested approach, it is less ergonomic but it is safe.
    #[inline]
    pub async fn map<F>(
        &mut self,
        resources: &[String],
        expiration: Duration,
        timeout: Duration,
        sleep: Duration,
        f: F,
    ) -> Result<F::Output, MapError>
    where
        F: Future + Send + 'static,
        F::Output: Send + 'static,
    {
        let lock_id = self
            .acquire(resources, expiration, timeout, sleep)
            .await
            .map_err(MapError::Acquire)?
            .ok_or(MapError::Timeout)?;
        let result = f.await;
        self.release(&lock_id).await.map_err(MapError::Release)?;
        Ok(result)
    }

    /// Calls [`MultiResourceLock::map`] with [`DEFAULT_EXPIRATION`], [`DEFAULT_TIMEOUT`] and [`DEFAULT_SLEEP`].
    #[inline]
    pub async fn map_default<F>(
        &mut self,
        resources: &[String],
        f: F,
    ) -> Result<F::Output, MapError>
    where
        F: Future + Send + 'static,
        F::Output: Send + 'static,
    {
        self.map(
            resources,
            DEFAULT_EXPIRATION,
            DEFAULT_TIMEOUT,
            DEFAULT_SLEEP,
            f,
        )
        .await
    }
}

/// Error for [`MultiResourceLock::map`].
#[derive(Debug, Display, Error)]
pub enum MapError {
    /// Timed out attempting to acquire the lock.
    Timeout,
    /// Failed to acquire lock: {0}
    Acquire(RedisError),
    /// Failed to release lock: {0}
    Release(RedisError),
}