Use generic lock-free queue for async threads

Queues used for communication between async threads and scheduler threads
have been replaced with lock-free queues.

Drivers using the driver_async functionality are not automatically locked
to the system anymore, and can be unloaded as any dynamically linked in
driver.

Scheduling of ready async jobs is now also interleaved in between other
jobs. Previously all ready async jobs was performed at once.

1 files changed, 13 insertions, 6 deletions

diff --git a/erts/doc/src/erl_driver.xml b/erts/doc/src/erl_driver.xml
index 2fb03954b6..8e18dd6657 100644
--- a/erts/doc/src/erl_driver.xml
+++ b/erts/doc/src/erl_driver.xml
@@ -1638,12 +1638,19 @@ ERL_DRV_EXT2TERM     char *buf, ErlDrvUInt len
       <fsummary>Cancel an asynchronous call</fsummary>
       <desc>
         <marker id="driver_async_cancel"></marker>
-        <p>This function cancels an asynchronous operation, by removing
-          it from the queue. Only functions in the queue can be
-          cancelled; if a function is executing, it's too late to
-          cancel it. The <c>async_free</c> function is also called.</p>
-        <p>The return value is 1 if the operation was removed from the
-          queue, otherwise 0.</p>
+        <p>This function used to cancel a scheduled asynchronous operation,
+	  if it was still in the queue. It returned 1 if it succeeded, and
+	  0 if it failed.</p>
+	<p>Since it could not guarantee success, it was more or less useless.
+	   The user had to implement synchronization of cancellation anyway.
+	   It also unnecessarily complicated the implementation. Therefore,
+	   as of OTP-R15B <c>driver_async_cancel()</c> is deprecated, and
+	   scheduled for removal in OTP-R16. It will currently always fail,
+	   and return 0.</p>
+	<warning><p><c>driver_async_cancel()</c> is deferred and will
+	            be removed in the OTP-R16 release.</p>
+	</warning>
+
       </desc>
     </func>
     <func>