1 files changed, 25 insertions, 17 deletions
diff --git a/src/library/scala/concurrent/ExecutionContext.scala b/src/library/scala/concurrent/ExecutionContext.scala
index fe684e4d46..f46f294387 100644
--- a/src/library/scala/concurrent/ExecutionContext.scala
+++ b/src/library/scala/concurrent/ExecutionContext.scala
@@ -25,21 +25,20 @@ import scala.annotation.implicitNotFound
  * and an implicit `ExecutionContext`. The implicit `ExecutionContext`
  * will be used to execute the callback.
  *
- * It is possible to simply import
+ * While it is possible to simply import
  * `scala.concurrent.ExecutionContext.Implicits.global` to obtain an
- * implicit `ExecutionContext`. This global context is a reasonable
- * default thread pool.
- *
- * However, application developers should carefully consider where they
- * want to set policy; ideally, one place per application (or per
- * logically-related section of code) will make a decision about
- * which `ExecutionContext` to use. That is, you might want to avoid
- * hardcoding `scala.concurrent.ExecutionContext.Implicits.global` all
- * over the place in your code.
- * One approach is to add `(implicit ec: ExecutionContext)`
- * to methods which need an `ExecutionContext`. Then import a specific
- * context in one place for the entire application or module,
- * passing it implicitly to individual methods.
+ * implicit `ExecutionContext`, application developers should carefully
+ * consider where they want to set execution policy;
+ * ideally, one place per application—or per logically related section of code—
+ * will make a decision about which `ExecutionContext` to use.
+ * That is, you will mostly want to avoid hardcoding, especially via an import,
+ * `scala.concurrent.ExecutionContext.Implicits.global`.
+ * The recommended approach is to add `(implicit ec: ExecutionContext)` to methods,
+ * or class constructor parameters, which need an `ExecutionContext`.
+ * 
+ * Then locally import a specific `ExecutionContext` in one place for the entire
+ * application or module, passing it implicitly to individual methods.
+ * Alternatively define a local implicit val with the required `ExecutionContext`.
  *
  * A custom `ExecutionContext` may be appropriate to execute code
  * which blocks on IO or performs long-running computations.
@@ -111,9 +110,18 @@ object ExecutionContext {
    * The explicit global `ExecutionContext`. Invoke `global` when you want to provide the global
    * `ExecutionContext` explicitly.
    *
-   * The default `ExecutionContext` implementation is backed by a work-stealing thread pool. By default,
-   * the thread pool uses a target number of worker threads equal to the number of
-   * [[https://docs.oracle.com/javase/8/docs/api/java/lang/Runtime.html#availableProcessors-- available processors]].
+   * The default `ExecutionContext` implementation is backed by a work-stealing thread pool.
+   * It can be configured via the following [[scala.sys.SystemProperties]]:
+   *
+   * `scala.concurrent.context.minThreads` = defaults to "1"
+   * `scala.concurrent.context.numThreads` = defaults to "x1" (i.e. the current number of available processors * 1)
+   * `scala.concurrent.context.maxThreads` = defaults to "x1" (i.e. the current number of available processors * 1)
+   * `scala.concurrent.context.maxExtraThreads` = defaults to "256"
+   *
+   * The pool size of threads is then `numThreads` bounded by `minThreads` on the lower end and `maxThreads` on the high end.
+   *
+   * The `maxExtraThreads` is the maximum number of extra threads to have at any given time to evade deadlock,
+   * see [[scala.concurrent.BlockContext]].
    *
    * @return the global `ExecutionContext`
    */