Add tests for examples from Nim in Action.

tests/niminaction/Chapter6/WikipediaStats/concurrency.nim

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+# See this page for info about the format https://wikitech.wikimedia.org/wiki/Analytics/Data/Pagecounts-all-sites
+import tables, parseutils, strutils, threadpool
+
+const filename = "pagecounts-20160101-050000"
+
+type
+  Stats = ref object
+    projectName, pageTitle: string
+    requests, contentSize: int
+
+proc `$`(stats: Stats): string =
+  "(projectName: $#, pageTitle: $#, requests: $#, contentSize: $#)" % [
+    stats.projectName, stats.pageTitle, $stats.requests, $stats.contentSize
+  ]
+
+proc parse(chunk: string): Stats =
+  # Each line looks like: en Main_Page 242332 4737756101
+  result = Stats(projectName: "", pageTitle: "", requests: 0, contentSize: 0)
+
+  var projectName = ""
+  var pageTitle = ""
+  var requests = ""
+  var contentSize = ""
+  for line in chunk.splitLines:
+    var i = 0
+    projectName.setLen(0)
+    i.inc parseUntil(line, projectName, Whitespace, i)
+    i.inc skipWhitespace(line, i)
+    pageTitle.setLen(0)
+    i.inc parseUntil(line, pageTitle, Whitespace, i)
+    i.inc skipWhitespace(line, i)
+    requests.setLen(0)
+    i.inc parseUntil(line, requests, Whitespace, i)
+    i.inc skipWhitespace(line, i)
+    contentSize.setLen(0)
+    i.inc parseUntil(line, contentSize, Whitespace, i)
+    i.inc skipWhitespace(line, i)
+
+    if requests.len == 0 or contentSize.len == 0:
+      # Ignore lines with either of the params that are empty.
+      continue
+
+    let requestsInt = requests.parseInt
+    if requestsInt > result.requests and projectName == "en":
+      result = Stats(
+        projectName: projectName,
+        pageTitle: pageTitle,
+        requests: requestsInt,
+        contentSize: contentSize.parseInt
+      )
+
+proc readChunks(filename: string, chunksize = 1000000): Stats =
+  result = Stats(projectName: "", pageTitle: "", requests: 0, contentSize: 0)
+  var file = open(filename)
+  var responses = newSeq[FlowVar[Stats]]()
+  var buffer = newString(chunksize)
+  var oldBufferLen = 0
+  while not endOfFile(file):
+    let readSize = file.readChars(buffer, oldBufferLen, chunksize - oldBufferLen) + oldBufferLen
+    var chunkLen = readSize
+
+    while chunkLen >= 0 and buffer[chunkLen - 1] notin NewLines:
+      # Find where the last line ends
+      chunkLen.dec
+
+    responses.add(spawn parse(buffer[0 .. <chunkLen]))
+    oldBufferLen = readSize - chunkLen
+    buffer[0 .. <oldBufferLen] = buffer[readSize - oldBufferLen .. ^1]
+
+  for resp in responses:
+    let statistic = ^resp
+    if statistic.requests > result.requests:
+      result = statistic
+
+  file.close()
+
+
+when isMainModule:
+  echo readChunks(filename)