-
Notifications
You must be signed in to change notification settings - Fork 509
/
IOApp.scala
384 lines (347 loc) · 14.3 KB
/
IOApp.scala
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
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
/*
* Copyright 2020-2022 Typelevel
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package cats.effect
import cats.effect.tracing.TracingConstants._
import cats.effect.unsafe.FiberMonitor
import scala.concurrent.{blocking, CancellationException}
import scala.util.control.NonFatal
import java.util.concurrent.{ArrayBlockingQueue, CountDownLatch}
import java.util.concurrent.atomic.AtomicInteger
/**
* The primary entry point to a Cats Effect application. Extend this trait rather than defining
* your own `main` method. This avoids the need to run [[IO.unsafeRunSync]] (or similar) on your
* own.
*
* `IOApp` takes care of the messy details of properly setting up (and tearing down) the
* [[unsafe.IORuntime]] needed to run the [[IO]] which represents your application. All of the
* associated thread pools (if relevant) will be configured with the assumption that your
* application is fully contained within the `IO` produced by the [[run]] method. Note that the
* exact details of how the runtime will be configured are very platform-specific. Part of the
* point of `IOApp` is to insulate users from the details of the underlying runtime (whether JVM
* or JavaScript).
*
* {{{
* object MyApplication extends IOApp {
* def run(args: List[String]) =
* for {
* _ <- IO.print("Enter your name: ")
* name <- IO.readln
* _ <- IO.println("Hello, " + name)
* } yield ExitCode.Success
* }
* }}}
*
* In the above example, `MyApplication` will be a runnable class with a `main` method, visible
* to Sbt, IntelliJ, or plain-old `java`. When run externally, it will print, read, and print in
* the obvious way, producing a final process exit code of 0. Any exceptions thrown within the
* `IO` will be printed to standard error and the exit code will be set to 1. In the event that
* the main [[Fiber]] (represented by the `IO` returned by `run`) is canceled, the runtime will
* produce an exit code of 1.
*
* Note that exit codes are an implementation-specific feature of the underlying runtime, as are
* process arguments. Naturally, all JVMs support these functions, as does NodeJS, but some
* JavaScript execution environments will be unable to replicate these features (or they simply
* may not make sense). In such cases, exit codes may be ignored and/or argument lists may be
* empty.
*
* Note that in the case of the above example, we would actually be better off using
* [[IOApp.Simple]] rather than `IOApp` directly, since we are neither using `args` nor are we
* explicitly producing a custom [[ExitCode]]:
*
* {{{
* object MyApplication extends IOApp.Simple {
* val run =
* for {
* _ <- IO.print("Enter your name: ")
* name <- IO.readln
* _ <- IO.println(s"Hello, " + name)
* } yield ()
* }
* }}}
*
* It is valid to define `val run` rather than `def run` because `IO`'s evaluation is lazy: it
* will only run when the `main` method is invoked by the runtime.
*
* In the event that the process receives an interrupt signal (`SIGINT`) due to Ctrl-C (or any
* other mechanism), it will immediately `cancel` the main fiber. Assuming this fiber is not
* within an `uncancelable` region, this will result in interrupting any current activities and
* immediately invoking any finalizers (see: [[IO.onCancel]] and [[IO.bracket]]). The process
* will not shut down until the finalizers have completed. For example:
*
* {{{
* object InterruptExample extends IOApp.Simple {
* val run =
* IO.bracket(startServer)(
* _ => IO.never)(
* server => IO.println("shutting down") *> server.close)
* }
* }}}
*
* If we assume the `startServer` function has type `IO[Server]` (or similar), this kind of
* pattern is very common. When this process receives a `SIGINT`, it will immediately print
* "shutting down" and run the `server.close` effect.
*
* One consequence of this design is it is possible to build applications which will ignore
* process interrupts. For example, if `server.close` runs forever, the process will ignore
* interrupts and will need to be cleaned up using `SIGKILL` (i.e. `kill -9`). This same
* phenomenon can be demonstrated by using [[IO.uncancelable]] to suppress all interruption
* within the application itself:
*
* {{{
* object Zombie extends IOApp.Simple {
* val run = IO.never.uncancelable
* }
* }}}
*
* The above process will run forever and ignore all interrupts. The only way it will shut down
* is if it receives `SIGKILL`.
*
* It is possible (though not necessary) to override various platform-specific runtime
* configuration options, such as `computeWorkerThreadCount` (which only exists on the JVM).
* Please note that the default configurations have been extensively benchmarked and are optimal
* (or close to it) in most conventional scenarios.
*
* However, with that said, there really is no substitute to benchmarking your own application.
* Every application and scenario is unique, and you will always get the absolute best results
* by performing your own tuning rather than trusting someone else's defaults. `IOApp`'s
* defaults are very ''good'', but they are not perfect in all cases. One common example of this
* is applications which maintain network or file I/O worker threads which are under heavy load
* in steady-state operations. In such a performance profile, it is usually better to reduce the
* number of compute worker threads to "make room" for the I/O workers, such that they all sum
* to the number of physical threads exposed by the kernel.
*
* @see
* [[IO]]
* @see
* [[run]]
* @see
* [[ResourceApp]]
* @see
* [[IOApp.Simple]]
*/
trait IOApp {
private[this] var _runtime: unsafe.IORuntime = null
/**
* The runtime which will be used by `IOApp` to evaluate the [[IO]] produced by the `run`
* method. This may be overridden by `IOApp` implementations which have extremely specialized
* needs, but this is highly unlikely to ever be truly needed. As an example, if an
* application wishes to make use of an alternative compute thread pool (such as
* `Executors.fixedThreadPool`), it is almost always better to leverage [[IO.evalOn]] on the
* value produced by the `run` method, rather than directly overriding `runtime`.
*
* In other words, this method is made available to users, but its use is strongly discouraged
* in favor of other, more precise solutions to specific use-cases.
*
* This value is guaranteed to be equal to [[unsafe.IORuntime.global]].
*/
protected def runtime: unsafe.IORuntime = _runtime
/**
* The configuration used to initialize the [[runtime]] which will evaluate the [[IO]]
* produced by `run`. It is very unlikely that users will need to override this method.
*/
protected def runtimeConfig: unsafe.IORuntimeConfig = unsafe.IORuntimeConfig()
/**
* Controls the number of worker threads which will be allocated to the compute pool in the
* underlying runtime. In general, this should be no ''greater'' than the number of physical
* threads made available by the underlying kernel (which can be determined using
* `Runtime.getRuntime().availableProcessors()`). For any application which has significant
* additional non-compute thread utilization (such as asynchronous I/O worker threads), it may
* be optimal to reduce the number of compute threads by the corresponding amount such that
* the total number of active threads exactly matches the number of underlying physical
* threads.
*
* In practice, tuning this parameter is unlikely to affect your application performance
* beyond a few percentage points, and the default value is optimal (or close to optimal) in
* ''most'' common scenarios.
*
* '''This setting is JVM-specific and will not compile on JavaScript.'''
*
* For more details on Cats Effect's runtime threading model please see
* [[https://typelevel.org/cats-effect/docs/thread-model]].
*/
protected def computeWorkerThreadCount: Int =
Math.max(2, Runtime.getRuntime().availableProcessors())
/**
* The entry point for your application. Will be called by the runtime when the process is
* started. If the underlying runtime supports it, any arguments passed to the process will be
* made available in the `args` parameter. The numeric value within the resulting [[ExitCode]]
* will be used as the exit code when the process terminates unless terminated exceptionally
* or by interrupt.
*
* @param args
* The arguments passed to the process, if supported by the underlying runtime. For example,
* `java com.company.MyApp --foo --bar baz` or `node com-mycompany-fastopt.js --foo --bar
* baz` would each result in `List("--foo", "--bar", "baz")`.
* @see
* [[IOApp.Simple!.run:cats\.effect\.IO[Unit]*]]
*/
def run(args: List[String]): IO[ExitCode]
final def main(args: Array[String]): Unit = {
// checked in openjdk 8-17; this attempts to detect when we're running under artificial environments, like sbt
val isForked = Thread.currentThread().getId() == 1
if (runtime == null) {
import unsafe.IORuntime
val installed = IORuntime installGlobal {
val (compute, compDown) =
IORuntime.createDefaultComputeThreadPool(runtime, threads = computeWorkerThreadCount)
val (blocking, blockDown) =
IORuntime.createDefaultBlockingExecutionContext()
val (scheduler, schedDown) =
IORuntime.createDefaultScheduler()
val fiberMonitor = FiberMonitor(compute)
val unregisterFiberMonitorMBean = IORuntime.registerFiberMonitorMBean(fiberMonitor)
IORuntime(
compute,
blocking,
scheduler,
fiberMonitor,
{ () =>
unregisterFiberMonitorMBean()
compDown()
blockDown()
schedDown()
},
runtimeConfig)
}
if (!installed) {
System
.err
.println(
"WARNING: Cats Effect global runtime already initialized; custom configurations will be ignored")
}
_runtime = IORuntime.global
}
if (isStackTracing) {
val liveFiberSnapshotSignal = sys
.props
.get("os.name")
.toList
.map(_.toLowerCase)
.filterNot(
_.contains("windows")
) // Windows does not support signals user overridable signals
.flatMap(_ => List("USR1", "INFO"))
liveFiberSnapshotSignal foreach { name =>
Signal.handle(name, _ => runtime.fiberMonitor.liveFiberSnapshot(System.err.print(_)))
}
}
val rt = Runtime.getRuntime()
val queue = new ArrayBlockingQueue[AnyRef](1)
val counter = new AtomicInteger(1)
val ioa = run(args.toList)
val fiber =
ioa.unsafeRunFiber(
{
counter.decrementAndGet()
queue.offer(new CancellationException("IOApp main fiber was canceled"))
()
},
{ t =>
counter.decrementAndGet()
queue.offer(t)
()
},
{ a =>
counter.decrementAndGet()
queue.offer(a)
()
}
)(runtime)
if (isStackTracing)
runtime.fiberMonitor.monitorSuspended(fiber)
def handleShutdown(): Unit = {
if (counter.compareAndSet(1, 0)) {
val cancelLatch = new CountDownLatch(1)
fiber.cancel.unsafeRunAsync(_ => cancelLatch.countDown())(runtime)
val timeout = runtimeConfig.shutdownHookTimeout
if (timeout.isFinite) {
blocking(cancelLatch.await(timeout.length, timeout.unit))
()
} else {
blocking(cancelLatch.await())
}
}
// Clean up after ourselves, relevant for running IOApps in sbt,
// otherwise scheduler threads will accumulate over time.
runtime.shutdown()
}
val hook = new Thread(() => handleShutdown())
hook.setName("io-cancel-hook")
try {
rt.addShutdownHook(hook)
} catch {
case _: IllegalStateException =>
// we're already being shut down
handleShutdown()
}
try {
val result = blocking(queue.take())
result match {
case ec: ExitCode =>
// Clean up after ourselves, relevant for running IOApps in sbt,
// otherwise scheduler threads will accumulate over time.
runtime.shutdown()
if (ec == ExitCode.Success) {
// Return naturally from main. This allows any non-daemon
// threads to gracefully complete their work, and managed
// environments to execute their own shutdown hooks.
if (isForked && NonDaemonThreadLogger.isEnabled())
new NonDaemonThreadLogger().start()
else
()
} else if (isForked) {
System.exit(ec.code)
}
case e: CancellationException =>
if (isForked)
// Do not report cancelation exceptions but still exit with an error code.
System.exit(1)
else
// if we're unforked, the only way to report cancelation is to throw
throw e
case NonFatal(t) =>
if (isForked) {
t.printStackTrace()
System.exit(1)
} else {
throw t
}
case t: Throwable =>
t.printStackTrace()
rt.halt(1)
}
} catch {
// this handles sbt when fork := false
case _: InterruptedException =>
hook.start()
rt.removeShutdownHook(hook)
Thread.currentThread().interrupt()
}
}
}
object IOApp {
/**
* A simplified version of [[IOApp]] for applications which ignore their process arguments and
* always produces [[ExitCode.Success]] (unless terminated exceptionally or interrupted).
*
* @see
* [[IOApp]]
*/
trait Simple extends IOApp {
def run: IO[Unit]
final def run(args: List[String]): IO[ExitCode] = run.as(ExitCode.Success)
}
}