Add metrics to count when worker blocked/respawned

core/jvm/src/main/scala/cats/effect/unsafe/WorkerThread.scala

@@ -867,6 +867,8 @@ private[effect] final class WorkerThread[P <: AnyRef](
       // This `WorkerThread` has already been prepared for blocking.
       // There is no need to spawn another `WorkerThread`.
     } else {
+      metrics.incrementBlockingCount()
+
       // Spawn a new `WorkerThread` to take the place of this thread, as the
       // current thread prepares to execute a blocking action.
 
@@ -902,6 +904,7 @@ private[effect] final class WorkerThread[P <: AnyRef](
         // a worker thread about to run blocking code is **not** parked, and
         // therefore, another worker thread would not even see it as a candidate
         // for unparking.
+        metrics.incrementRespawnCount()
         val idx = index
         val clone =
           new WorkerThread(
@@ -971,6 +974,14 @@ private[effect] object WorkerThread {
     private[this] var idleTime: Long = 0
     def getIdleTime(): Long = idleTime
     def addIdleTime(x: Long): Unit = idleTime += x
+
+    private[this] var blockingCount: Long = 0
+    def getBlockingCount(): Long = blockingCount
+    def incrementBlockingCount(): Unit = blockingCount += 1
+
+    private[this] var respawnCount: Long = 0
+    def getRespawnCount(): Long = respawnCount
+    def incrementRespawnCount(): Unit = respawnCount += 1
   }
 
 }

core/jvm/src/main/scala/cats/effect/unsafe/metrics/WorkStealingPoolMetrics.scala

@@ -103,6 +103,18 @@ trait WorkerThreadMetrics {
    */
   def idleTime(): Long
 
+  /**
+   * The total number of times that this WorkerThread has switched to a blocking thread and been
+   * replaced.
+   */
+  def blockingCount(): Long
+
+  /**
+   * The total number of times that this WorkerThread has been replaced by a newly spawned
+   * thread.
+   */
+  def respawnCount(): Long
+
   /**
    * LocalQueue-specific metrics of this WorkerThread.
    */
@@ -244,6 +256,8 @@ object WorkStealingPoolMetrics {
 
     private val metrics = wstp.metrices(idx)
     def idleTime(): Long = metrics.getIdleTime()
+    def blockingCount(): Long = metrics.getBlockingCount()
+    def respawnCount(): Long = metrics.getBlockingCount()
 
     val localQueue: LocalQueueMetrics = localQueueMetrics(wstp.localQueues(index))
     val timerHeap: TimerHeapMetrics = timerHeapMetrics(wstp.sleepers(index))