Don't reopen the coverage file each time; on windows that is very slow.

src/main/scala/scoverage/IOUtils.scala

@@ -14,10 +14,13 @@ object IOUtils {
  def clean(dataDir: String): Unit = clean(new File(dataDir))
 
  def coverageFile(dataDir: File): File = coverageFile(dataDir.getAbsolutePath)
- def coverageFile(dataDir: String): File = new File(dataDir + "/" + CoverageFileName)
+ def coverageFile(dataDir: String): File = new File(dataDir, CoverageFileName)
 
+ /**
+ * @return the measurement file for the current thread.
+ */
  def measurementFile(dataDir: File): File = measurementFile(dataDir.getAbsolutePath)
- def measurementFile(dataDir: String): File = new File(dataDir + "/" + MeasurementsPrefix + Thread.currentThread.getId)
+ def measurementFile(dataDir: String): File = new File(dataDir, MeasurementsPrefix + Thread.currentThread.getId)
 
  def findMeasurementFiles(dataDir: String): Array[File] = findMeasurementFiles(new File(dataDir))
  def findMeasurementFiles(dataDir: File): Array[File] = dataDir.listFiles(new FileFilter {
@@ -141,4 +144,4 @@ object IOUtils {
  reader.close()
  coverage
  }
-}
+}

src/main/scala/scoverage/Invoker.scala

@@ -5,6 +5,8 @@ import java.io.FileWriter
 /** @author Stephen Samuel */
 object Invoker {
 
+ val threadFile = new ThreadLocal[FileWriter]
+
  /**
  * We record that the given id has been invoked by appending its id to the coverage
  * data file.
@@ -23,9 +25,12 @@ object Invoker {
  def invoked(id: Int, dataDir: String) = {
  // Each thread writes to a separate measurement file, to reduce contention
  // and because file appends via FileWriter are not atomic on Windows.
- val file = IOUtils.measurementFile(dataDir)
- val writer = new FileWriter(file, true)
- writer.append(id.toString + ';')
- writer.close()
+ var writer = threadFile.get()
+ if (writer == null) {
+ val file = IOUtils.measurementFile(dataDir)
+ writer = new FileWriter(file, true)
+ threadFile.set(writer)
+ }
+ writer.append(id.toString + ';').flush()
  }
-}
+}