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
|
/*
* Copyright (C) 2012 Typesafe Inc. <http://www.typesafe.com>
*/
package scala.async
package continuations
import scala.language.experimental.macros
import scala.reflect.macros.Context
import scala.util.continuations._
import scala.async.internal.{AsyncMacro, AsyncUtils}
trait AsyncBaseWithCPSFallback extends internal.AsyncBase {
/* Fall-back for `await` using CPS plugin.
*
* Note: This method is public, but is intended only for internal use.
*/
def awaitFallback[T](awaitable: futureSystem.Fut[T]): T @cps[futureSystem.Fut[Any]]
override protected[async] def fallbackEnabled = true
/* Implements `async { ... }` using the CPS plugin.
*/
protected def cpsBasedAsyncImpl[T: c.WeakTypeTag](c: Context)
(body: c.Expr[T])
(execContext: c.Expr[futureSystem.ExecContext]): c.Expr[futureSystem.Fut[T]] = {
import c.universe._
def lookupClassMember(clazz: String, name: String) = {
val asyncTrait = c.mirror.staticClass(clazz)
val tpe = asyncTrait.asType.toType
tpe.member(newTermName(name)).ensuring(_ != NoSymbol, s"$clazz.$name")
}
def lookupObjectMember(clazz: String, name: String) = {
val moduleClass = c.mirror.staticModule(clazz).moduleClass
val tpe = moduleClass.asType.toType
tpe.member(newTermName(name)).ensuring(_ != NoSymbol, s"$clazz.$name")
}
AsyncUtils.vprintln("AsyncBaseWithCPSFallback.cpsBasedAsyncImpl")
val symTab = c.universe.asInstanceOf[reflect.internal.SymbolTable]
val futureSystemOps = futureSystem.mkOps(symTab)
val awaitSym = lookupObjectMember("scala.async.Async", "await")
val awaitFallbackSym = lookupClassMember("scala.async.continuations.AsyncBaseWithCPSFallback", "awaitFallback")
// replace `await` invocations with `awaitFallback` invocations
val awaitReplacer = new Transformer {
override def transform(tree: Tree): Tree = tree match {
case Apply(fun @ TypeApply(_, List(futArgTpt)), args) if fun.symbol == awaitSym =>
val typeApp = treeCopy.TypeApply(fun, atPos(tree.pos)(Ident(awaitFallbackSym)), List(atPos(tree.pos)(TypeTree(futArgTpt.tpe))))
treeCopy.Apply(tree, typeApp, args.map(arg => c.resetAllAttrs(arg.duplicate)))
case _ =>
super.transform(tree)
}
}
val bodyWithAwaitFallback = awaitReplacer.transform(body.tree)
/* generate an expression that looks like this:
reset {
val f = future { ... }
...
val x = awaitFallback(f)
...
future { expr }
}.asInstanceOf[Future[T]]
*/
def spawn(expr: Tree) = futureSystemOps.spawn(expr.asInstanceOf[futureSystemOps.universe.Tree], execContext.tree.asInstanceOf[futureSystemOps.universe.Tree]).asInstanceOf[Tree]
val bodyWithFuture = {
val tree = bodyWithAwaitFallback match {
case Block(stmts, expr) => Block(stmts, spawn(expr))
case expr => spawn(expr)
}
c.Expr[futureSystem.Fut[Any]](c.resetAllAttrs(tree.duplicate))
}
val bodyWithReset: c.Expr[futureSystem.Fut[Any]] = reify {
reset { bodyWithFuture.splice }
}
val bodyWithCast = futureSystemOps.castTo[T](bodyWithReset.asInstanceOf[futureSystemOps.universe.Expr[futureSystem.Fut[Any]]]).asInstanceOf[c.Expr[futureSystem.Fut[T]]]
AsyncUtils.vprintln(s"CPS-based async transform expands to:\n${bodyWithCast.tree}")
bodyWithCast
}
override def asyncImpl[T: c.WeakTypeTag](c: Context)
(body: c.Expr[T])
(execContext: c.Expr[futureSystem.ExecContext]): c.Expr[futureSystem.Fut[T]] = {
AsyncUtils.vprintln("AsyncBaseWithCPSFallback.asyncImpl")
val asyncMacro = AsyncMacro(c, futureSystem)
if (!asyncMacro.reportUnsupportedAwaits(body.tree.asInstanceOf[asyncMacro.global.Tree], report = fallbackEnabled))
super.asyncImpl[T](c)(body)(execContext) // no unsupported awaits
else
cpsBasedAsyncImpl[T](c)(body)(execContext) // fallback to CPS
}
}
|
