Document System.Threading APIs (#3229)

* Document System.Threading APIs

* Additional documentation for Channel

* suggestions by stephentoub and tarekgh

* suggestions by rpetrusha

Co-Authored-By: Ron Petrusha <[email protected]>

* additional abstract removal

Author: carlossanlop

xml/System.Threading.Channels/Channel.xml

@@ -103,7 +103,7 @@
       </TypeParameters>
       <Parameters />
       <Docs>
-        <typeparam name="T">To be added.</typeparam>
+        <typeparam name="T">The type of data in the channel.</typeparam>
         <summary>Creates an unbounded channel usable by any number of readers and writers concurrently.</summary>
         <returns>The created channel.</returns>
         <remarks>To be added.</remarks>

xml/System.Threading.Channels/ChannelOptions.xml

@@ -33,7 +33,7 @@
       </AssemblyInfo>
       <Parameters />
       <Docs>
-        <summary>To be added.</summary>
+        <summary>Initializes an instance of the <see cref="T:System.Threading.Channels.ChannelOptions" /> class.</summary>
         <remarks>To be added.</remarks>
       </Docs>
     </Member>

xml/System.Threading.Channels/ChannelReader`1.xml

@@ -37,7 +37,7 @@
       </AssemblyInfo>
       <Parameters />
       <Docs>
-        <summary>To be added.</summary>
+        <summary>Initializes an instance of the <see cref="T:System.Threading.Channels.ChannelReader`1" /> class.</summary>
         <remarks>To be added.</remarks>
       </Docs>
     </Member>

xml/System.Threading.Channels/ChannelWriter`1.xml

@@ -37,7 +37,7 @@
       </AssemblyInfo>
       <Parameters />
       <Docs>
-        <summary>To be added.</summary>
+        <summary>Initializes an instance of the <see cref="T:System.Threading.Channels.ChannelWriter`1" /> class.</summary>
         <remarks>To be added.</remarks>
       </Docs>
     </Member>

xml/System.Threading.Channels/Channel`1.xml

@@ -41,7 +41,7 @@
       </AssemblyInfo>
       <Parameters />
       <Docs>
-        <summary>To be added.</summary>
+        <summary>Initializes an instance of the <see cref="T:System.Threading.Channels.Channel`1" /> class.</summary>
         <remarks>To be added.</remarks>
       </Docs>
     </Member>

xml/System.Threading.Channels/Channel`2.xml

@@ -39,7 +39,7 @@
       </AssemblyInfo>
       <Parameters />
       <Docs>
-        <summary>To be added.</summary>
+        <summary>Initializes an instance of the <see cref="T:System.Threading.Channels.Channel`2" /> class.</summary>
         <remarks>To be added.</remarks>
       </Docs>
     </Member>

xml/System.Threading.Channels/UnboundedChannelOptions.xml

@@ -33,7 +33,7 @@
       </AssemblyInfo>
       <Parameters />
       <Docs>
-        <summary>To be added.</summary>
+        <summary>Initializes a new instance of the <see cref="T:System.Threading.Channels.UnboundedChannelOptions" /> class.</summary>
         <remarks>To be added.</remarks>
       </Docs>
     </Member>

xml/System.Threading.Tasks/Task.xml

@@ -3040,8 +3040,8 @@ Task t Status: RanToCompletion, Result: 42
         <ReturnType>System.Boolean</ReturnType>
       </ReturnValue>
       <Docs>
-        <summary>To be added.</summary>
-        <value>To be added.</value>
+        <summary>Gets whether the task ran to completion.</summary>
+        <value><see langword="true" /> if the task ran to completion; otherwise <see langword="false" />.</value>
         <remarks>To be added.</remarks>
       </Docs>
     </Member>

xml/System.Threading/Thread.xml

@@ -1826,9 +1826,17 @@ Main thread: ThreadProc.Join has returned.  Press Enter to end program.
       </ReturnValue>
       <Parameters />
       <Docs>
-        <summary>To be added.</summary>
-        <returns>To be added.</returns>
-        <remarks>To be added.</remarks>
+        <summary>Gets an ID used to indicate on which processor the current thread is executing.</summary>
+        <returns>An integer representing the cached processor ID.</returns>
+         <remarks>
+           <format type="text/markdown"><![CDATA[
+
+## Remarks
+
+This value is cached and periodically refreshed. It may be stale by the time it's used: consuming code must not rely on its accuracy for correctness.
+
+           ]]></format>
+         </remarks>
       </Docs>
     </Member>
     <Member MemberName="GetData">