首页 > 代码库 > Scalaz（58）－ scalaz-stream: fs2-并行运算示范，fs2 parallel processing
Scalaz（58）－ scalaz-stream: fs2-并行运算示范，fs2 parallel processing
从表面上来看，Stream代表一连串无穷数据元素。一连串的意思是元素有固定的排列顺序，所以对元素的运算也必须按照顺序来：完成了前面的运算再跟着进行下一个元素的运算。这样来看，Stream应该不是很好的并行运算工具。但是，fs2所支持的并行运算方式不是以数据元素而是以?Stream为运算单位的：fs2支持多个Stream同时进行运算，如merge函数。所以fs2使Stream的并行运算成为了可能。
一般来说，我们可能在Stream的几个状态节点要求并行运算：
1、同时运算多个数据源头来产生不排序的数据元素
2、同时对获取的一连串数据元素进行处理，如：map（update）,filter等等
3、同时将一连串数据元素无序存入终点（Sink）
我们可以创建一个例子来示范fs2的并行运算：?模拟从3个文件中读取字串，然后统计在这3个文件中母音出现的次数。假设文件读取和母音统计是有任意时间延迟的（latency）,我们看看如何进行并行运算及并行运算能有多少效率上的提升。我们先设定一些跟踪和模拟延迟的帮助函数：
1 def log[A](prompt: String): Pipe[Task,A,A] = _.evalMap { a => Task.delay{ println(s"$prompt>"); a }}2 //> log: [A](prompt: String)fs2.Pipe[fs2.Task,A,A]3 def randomDelay[A](max: FiniteDuration): Pipe[Task,A,A] = _.evalMap { a =>4 val delay: Task[Int] = Task.delay { scala.util.Random.nextInt(max.toMillis.toInt) }5 delay.flatMap {d => Task.now(a).schedule(d.millis) }6 } //> randomDelay: [A](max: scala.concurrent.duration.FiniteDuration)fs2.Pipe[fs2.log是个跟踪函数，randomDelay是个延迟模拟函数，模拟在max内的任意时间延迟。
与scalaz-stream-0.8不同，fs2重新实现了文件操作功能：不再依赖java的字串（string）处理功能。也不再依赖scodec的二进制数据转换功能。下面是fs2的文件读取方法示范：
1 val s1 = io.file.readAll[Task](java.nio.file.Paths.get("/Users/tiger-macpro/basic/BasicBackend.scala"),1024)2 //> s1 : fs2.Stream[fs2.Task,Byte] = evalScope(Scope(Bind(Eval(Snapshot),<function1>))).flatMap(<function1>)3 val s2 = io.file.readAll[Task](java.nio.file.Paths.get("/Users/tiger-macpro/basic/DatabaseConfig.scala"),1024)4 //> s2 : fs2.Stream[fs2.Task,Byte] = evalScope(Scope(Bind(Eval(Snapshot),<function1>))).flatMap(<function1>)5 val s3 = io.file.readAll[Task](java.nio.file.Paths.get("/Users/tiger-macpro/basic/BasicProfile.scala"),1024)6 //> s3 : fs2.Stream[fs2.Task,Byte] = evalScope(Scope(Bind(Eval(Snapshot),<function1>))).flatMap(<function1>)fs2.io.file.readAll函数的款式如下：
def readAll[F[_]](path: Path, chunkSize: Int)(implicit F: Effect[F]): Stream[F, Byte] ={...}readAll分批（by chunks）从文件中读取Byte类型数据（当返回数据量小于chunkSize代表完成读取），返回结果类型是Stream[F,Byte]。我们需要进行Byte>>>String转换及分行等处理。fs2在text对象里提供了相关函数：
object text { private val utf8Charset = Charset.forName("UTF-8") /** Converts UTF-8 encoded byte stream to a stream of `String`. */ def utf8Decode[F[_]]: Pipe[F, Byte, String] = _.chunks.through(utf8DecodeC) /** Converts UTF-8 encoded `Chunk[Byte]` inputs to `String`. */ def utf8DecodeC[F[_]]: Pipe[F, Chunk[Byte], String] = { /** * Returns the number of continuation bytes if `b` is an ASCII byte or a * leading byte of a multi-byte sequence, and -1 otherwise. */ def continuationBytes(b: Byte): Int = { if ((b & 0x80) == 0x00) 0 // ASCII byte else if ((b & 0xE0) == 0xC0) 1 // leading byte of a 2 byte seq else if ((b & 0xF0) == 0xE0) 2 // leading byte of a 3 byte seq else if ((b & 0xF8) == 0xF0) 3 // leading byte of a 4 byte seq else -1 // continuation byte or garbage }.../** Encodes a stream of `String` in to a stream of bytes using the UTF-8 charset. */ def utf8Encode[F[_]]: Pipe[F, String, Byte] = _.flatMap(s => Stream.chunk(Chunk.bytes(s.getBytes(utf8Charset)))) /** Encodes a stream of `String` in to a stream of `Chunk[Byte]` using the UTF-8 charset. */ def utf8EncodeC[F[_]]: Pipe[F, String, Chunk[Byte]] = _.map(s => Chunk.bytes(s.getBytes(utf8Charset))) /** Transforms a stream of `String` such that each emitted `String` is a line from the input. */ def lines[F[_]]: Pipe[F, String, String] = {...utf8Encode,utf8Decode,lines这几个函数正是我们需要的，它们都是Pipe类型。我们可以把这几个Pipe直接用through接到Stream上：
1 val startTime = System.currentTimeMillis //> startTime : Long = 1472444756321 2 val s1lines = s1.through(text.utf8Decode).through(text.lines) 3 .through(randomDelay(10 millis)).runFold(0)((b,_) => b + 1).unsafeRun 4 //> s1lines : Int = 479 5 println(s"reading s1 $s1lines lines in ${System.currentTimeMillis - startTime}ms") 6 //> reading s1 479 lines in 5370ms 7 8 val startTime2 = System.currentTimeMillis //> startTime2 : Long = 1472444761691 9 val s2lines = s2.through(text.utf8Decode).through(text.lines)10 .through(randomDelay(10 millis)).runFold(0)((b,_) => b + 1).unsafeRun11 //> s2lines : Int = 17412 println(s"reading s2 $s2lines lines in ${System.currentTimeMillis - startTime2}ms")13 //> reading s2 174 lines in 1923ms14 val startTime3 = System.currentTimeMillis //> startTime3 : Long = 147244476361415 val s3lines = s3.through(text.utf8Decode).through(text.lines)16 .through(randomDelay(10 millis)).runFold(0)((b,_) => b + 1).unsafeRun17 //> s3lines : Int = 17418 println(s"reading s3 $s3lines lines in ${System.currentTimeMillis - startTime3}ms")19 //> reading s3 174 lines in 1928ms20 println(s"reading all three files ${s1lines+s2lines+s3lines} total lines in ${System.currentTimeMillis - startTime}ms")21 //> reading all three files 827 total lines in 9221ms在以上的例子里我们用runFold函数统计文件的文字行数并在读取过程中用randomDelay来制造了随意长度的拖延。上面3个文件的字串读取和转换处理一共877行、9221ms。
我们知道fs2的并行运算函数concurrent.join函数类型款式是这样的：
def join[F[_],O](maxOpen: Int)(outer: Stream[F,Stream[F,O]])(implicit F: Async[F]): Stream[F,O] = {...}join运算的对象outer是个两层Stream（Streams of Stream）：Stream[F,Stream[F,P]]，我们需要先进行类型款式调整：
1 val lines1 = s1.through(text.utf8Decode).through(text.lines).through(randomDelay(10 millis))2 //> lines1 : fs2.Stream[fs2.Task,String] = evalScope(Scope(Bind(Eval(Snapshot),<function1>))).flatMap(<function1>).flatMap(<function1>)3 val lines2 = s2.through(text.utf8Decode).through(text.lines).through(randomDelay(10 millis))4 //> lines2 : fs2.Stream[fs2.Task,String] = evalScope(Scope(Bind(Eval(Snapshot),<function1>))).flatMap(<function1>).flatMap(<function1>)5 val lines3 = s3.through(text.utf8Decode).through(text.lines).through(randomDelay(10 millis))6 //> lines3 : fs2.Stream[fs2.Task,String] = evalScope(Scope(Bind(Eval(Snapshot),<function1>))).flatMap(<function1>).flatMap(<function1>)7 val ss: Stream[Task,Stream[Task,String]] = Stream(lines1,lines2,lines3)8 //> ss : fs2.Stream[fs2.Task,fs2.Stream[fs2.Task,String]] = Segment(Emit(Chunk(evalScope(Scope(Bind(Eval(Snapshot),<function1>))).flatMap(<function1>).flatMap(<function1>), evalScope(Scope(Bind(Eval(Snapshot),<function1>))).flatMap(<function1>).flatMap(<function1>), evalScope(Scope(Bind(Eval(Snapshot),<function1>))).flatMap(<function1>).flatMap(<function1>))))现在这个ss的类型复合我们的要求。我们可以测试一下并行运算的效率：
1 val ss_start = System.currentTimeMillis //> ss_start : Long = 14724499626982 val ss_lines = fs2.concurrent.join(3)(ss).runFold(0)((b,_) => b + 1).unsafeRun3 //> ss_lines : Int = 8274 println(s"parallel reading all files ${ss_lines} total lines in ${System.currentTimeMillis - ss_start}ms")5 //> parallel reading all files 827 total lines in 5173ms读取同等行数但只用了5173ms，与之前的9221ms相比，大约有成倍的提速。
join(3)(ss)返回了一个合并的Stream，类型是Stream[Task,String]。我们可以运算这个Stream里母音出现的频率。我们先设计这个统计函数：
1 //c 是个vowl2 def vowls(c: Char): Boolean = List(‘A‘,‘E‘,‘I‘,‘O‘,‘U‘).contains(c)3 //> vowls: (c: Char)Boolean4 //直接用scala标准库实现5 def pipeVowlsCount: Pipe[Task,String,Map[Char,Int]] =6 _.evalMap (text => Task.delay{7 text.toUpperCase.toList.filter(vowls).groupBy(s => s).mapValues(_.size)8 }.schedule((text.length / 10).millis)) //> pipeVowlsCount: => fs2.Pipe[fs2.Task,String,Map[Char,Int]]注意我们使用了text => Task.delay{...}.schedule(d)，实际上我们完全可以用 text => Thread.sleep(d)，但是这样会造成了不纯代码，所以我们用evalMap来实现纯代码运算。试试统计全部字串内母音出现的总数：
1 import scalaz.{Monoid} 2 //为runFold提供一个Map[Char,Int]Monoid实例 3 implicit object mapMonoid extends Monoid[Map[Char,Int]] { 4 def zero: Map[Char,Int] = Map() 5 def append(m1: Map[Char,Int], m2: => Map[Char,Int]): Map[Char,Int] = { 6 (m1.keySet ++ m2.keySet).map { k => 7 (k, m1.getOrElse(k,0) + m2.getOrElse(k,0)) 8 }.toMap 9 }10 }11 val vc_start = System.currentTimeMillis //> vc_start : Long = 147246477246512 val vowlsLine = fs2.concurrent.join(3)(ss).through(pipeVowlsCount)13 .runFold(Map[Char,Int]())(mapMonoid.append(_,_)).unsafeRun14 ?//> vowlsLine : scala.collection.immutable.Map[Char,Int] = Map(E -> 3381, U - ?838, A -> 2361, I -> 2031, O -> 1824)15 println(s"parallel reading all files and counted vowls sequencially in ${System.currentTimeMillis - vc_start}ms")16 //> parallel reading all files and counted vowls sequencially in 10466ms我们必须为runFold提供一个Monoid[Map[Char,Int]]实例mapMonoid。
那?我们又如何实现统计功能的并行运算呢? fs2.concurrent.join(maxOpen)(...)函数能把一个Stream截成maxOpen数的子Stream，然后对这些子Stream进行并行运算。那么我们又如何转换Stream[F,Stream[F,O]]类型呢？我们必须把Stream[F,O]的O升格成Stream[F,O]。我们先用一个函数来把O转换成Map[Char,Int]，然后把这个函数升格成Stream[Task,Map[Char,Int]，这个可以用Stream.eval实现：
1 def fVowlsCount(text: String): Map[Char,Int] =2 text.toUpperCase.toList.filter(vowls).groupBy(s => s).mapValues(_.size)3 //> fVowlsCount: (text: String)Map[Char,Int]4 val parVowlsLine: Stream[Task,Stream[Task,Map[Char,Int]]] = fs2.concurrent.join(3)(ss)5 .map {text => Stream.eval(Task {fVowlsCount(text)}.schedule((text.length / 10).millis))}6 //> parVowlsLine : fs2.Stream[fs2.Task,fs2.Stream[fs2.Task,Map[Char,Int]]] = attemptEval(Task).flatMap(<function1>).flatMap(<function1>).mapChunks(<function1>)我们来检查一下运行效率：
1 val parvc_start = System.currentTimeMillis //> parvc_start : Long = 14724658446942 fs2.concurrent.join(8)(parVowlsLine)3 .runFold(Map[Char,Int]())(mapMonoid.append(_,_)).unsafeRun4 //> res0: scala.collection.immutable.Map[Char,Int] = Map(E -> 3381, U -> 838, A-> 2361, I -> 2031, O -> 1824)5 println(s"parallel reading all files and counted vowls in ${System.currentTimeMillis - parvc_start}ms")6 //> parallel reading all files and counted vowls in 4984ms并行运算只需要4985ms，而流程运算需要10466+(9221-5173)=14xxx，这里有3，4倍的速度提升。
下面是这次讨论的示范源代码：
1 import fs2._ 2 import scala.language.{higherKinds,implicitConversions,postfixOps} 3 import scala.concurrent.duration._ 4 object fs2Merge { 5 implicit val strategy = Strategy.fromFixedDaemonPool(4) 6 implicit val scheduler = Scheduler.fromFixedDaemonPool(2) 7 def log[A](prompt: String): Pipe[Task,A,A] = _.evalMap { a => Task.delay{ println(s"$prompt>"); a }} 8 def randomDelay[A](max: FiniteDuration): Pipe[Task,A,A] = _.evalMap { a => 9 val delay: Task[Int] = Task.delay { scala.util.Random.nextInt(max.toMillis.toInt) }10 delay.flatMap {d => Task.now(a).schedule(d.millis) }11 }12 13 val s1 = io.file.readAll[Task](java.nio.file.Paths.get("/Users/tiger-macpro/basic/BasicBackend.scala"),1024)14 val s2 = io.file.readAll[Task](java.nio.file.Paths.get("/Users/tiger-macpro/basic/DatabaseConfig.scala"),1024)15 val s3 = io.file.readAll[Task](java.nio.file.Paths.get("/Users/tiger-macpro/basic/BasicProfile.scala"),1024)16 17 18 val startTime = System.currentTimeMillis19 val s1lines = s1.through(text.utf8Decode).through(text.lines)20 .through(randomDelay(10 millis)).runFold(0)((b,_) => b + 1).unsafeRun21 println(s"reading s1 $s1lines lines in ${System.currentTimeMillis - startTime}ms")22 23 val startTime2 = System.currentTimeMillis24 val s2lines = s2.through(text.utf8Decode).through(text.lines)25 .through(randomDelay(10 millis)).runFold(0)((b,_) => b + 1).unsafeRun26 println(s"reading s2 $s2lines lines in ${System.currentTimeMillis - startTime2}ms")27 val startTime3 = System.currentTimeMillis28 val s3lines = s3.through(text.utf8Decode).through(text.lines)29 .through(randomDelay(10 millis)).runFold(0)((b,_) => b + 1).unsafeRun30 println(s"reading s3 $s3lines lines in ${System.currentTimeMillis - startTime3}ms")31 println(s"reading all three files ${s1lines+s2lines+s3lines} total lines in ${System.currentTimeMillis - startTime}ms")32 val lines1 = s1.through(text.utf8Decode).through(text.lines).through(randomDelay(10 millis))33 val lines2 = s2.through(text.utf8Decode).through(text.lines).through(randomDelay(10 millis))34 val lines3 = s3.through(text.utf8Decode).through(text.lines).through(randomDelay(10 millis))35 val ss: Stream[Task,Stream[Task,String]] = Stream(lines1,lines2,lines3)36 val ss_start = System.currentTimeMillis37 val ss_lines = fs2.concurrent.join(3)(ss).runFold(0)((b,_) => b + 1).unsafeRun38 println(s"parallel reading all files ${ss_lines} total lines in ${System.currentTimeMillis - ss_start}ms")39 40 //c 是个vowl41 def vowls(c: Char): Boolean = List(‘A‘,‘E‘,‘I‘,‘O‘,‘U‘).contains(c)42 //直接用scala标准库实现43 def pipeVowlsCount: Pipe[Task,String,Map[Char,Int]] =44 _.evalMap (text => Task.delay{45 text.toUpperCase.toList.filter(vowls).groupBy(s => s).mapValues(_.size)46 }.schedule((text.length / 10).millis))47 48 import scalaz.{Monoid}49 //为runFold提供一个Map[Char,Int]Monoid实例50 implicit object mapMonoid extends Monoid[Map[Char,Int]] {51 def zero: Map[Char,Int] = Map()52 def append(m1: Map[Char,Int], m2: => Map[Char,Int]): Map[Char,Int] = {53 (m1.keySet ++ m2.keySet).map { k =>54 (k, m1.getOrElse(k,0) + m2.getOrElse(k,0))55 }.toMap56 }57 }58 val vc_start = System.currentTimeMillis59 val vowlsLine = fs2.concurrent.join(3)(ss).through(pipeVowlsCount)60 .runFold(Map[Char,Int]())(mapMonoid.append(_,_)).unsafeRun61 println(s"parallel reading all files and counted vowls sequencially in ${System.currentTimeMillis - vc_start}ms")62 def fVowlsCount(text: String): Map[Char,Int] =63 text.toUpperCase.toList.filter(vowls).groupBy(s => s).mapValues(_.size)64 val parVowlsLine: Stream[Task,Stream[Task,Map[Char,Int]]] = fs2.concurrent.join(3)(ss)65 .map {text => Stream.eval(Task {fVowlsCount(text)}.schedule((text.length / 10).millis))}66 val parvc_start = System.currentTimeMillis67 fs2.concurrent.join(8)(parVowlsLine)68 .runFold(Map[Char,Int]())(mapMonoid.append(_,_)).unsafeRun69 println(s"parallel reading all files and counted vowls in ${System.currentTimeMillis - parvc_start}ms") 70 }
Scalaz（58）－ scalaz-stream: fs2-并行运算示范，fs2 parallel processing
声明：以上内容来自用户投稿及互联网公开渠道收集整理发布，本网站不拥有所有权，未作人工编辑处理，也不承担相关法律责任，若内容有误或涉及侵权可进行投诉： 投诉/举报 工作人员会在5个工作日内联系你，一经查实，本站将立刻删除涉嫌侵权内容。