Add WritableStreamDefaultController.releaseBackpressure()

Author: MattiasBuelens

reference-implementation/lib/WritableStreamDefaultController-impl.js

@@ -21,6 +21,14 @@ exports.implementation = class WritableStreamDefaultControllerImpl {
     aos.WritableStreamDefaultControllerError(this, e);
   }
 
+  releaseBackpressure() {
+    const state = this._stream._state;
+    if (state !== 'writable') {
+      return;
+    }
+    aos.WritableStreamDefaultControllerReleaseBackpressure(this);
+  }
+
   [AbortSteps](reason) {
     const result = this._abortAlgorithm(reason);
     aos.WritableStreamDefaultControllerClearAlgorithms(this);

reference-implementation/lib/WritableStreamDefaultController.webidl

@@ -2,4 +2,5 @@
 interface WritableStreamDefaultController {
   readonly attribute AbortSignal signal;
   void error(optional any e);
+  void releaseBackpressure();
 };

reference-implementation/lib/abstract-ops/writable-streams.js

@@ -27,6 +27,7 @@ Object.assign(exports, {
   WritableStreamDefaultControllerClearAlgorithms,
   WritableStreamDefaultControllerError,
   WritableStreamDefaultControllerErrorIfNeeded,
+  WritableStreamDefaultControllerReleaseBackpressure,
   WritableStreamDefaultWriterAbort,
   WritableStreamDefaultWriterClose,
   WritableStreamDefaultWriterCloseWithErrorPropagation,
@@ -543,6 +544,7 @@ function SetUpWritableStreamDefaultController(stream, controller, startAlgorithm
 
   controller._abortController = new AbortController();
   controller._started = false;
+  controller._releaseBackpressure = false;
 
   controller._strategySizeAlgorithm = sizeAlgorithm;
   controller._strategyHWM = highWaterMark;
@@ -657,6 +659,9 @@ function WritableStreamDefaultControllerErrorIfNeeded(controller, error) {
 }
 
 function WritableStreamDefaultControllerGetBackpressure(controller) {
+  if (controller._releaseBackpressure === true) {
+    return false;
+  }
   const desiredSize = WritableStreamDefaultControllerGetDesiredSize(controller);
   return desiredSize <= 0;
 }
@@ -727,6 +732,19 @@ function WritableStreamDefaultControllerProcessWrite(controller, chunk) {
   );
 }
 
+function WritableStreamDefaultControllerReleaseBackpressure(controller) {
+  const stream = controller._stream;
+  assert(stream._state === 'writable');
+
+  controller._releaseBackpressure = true;
+
+  if (WritableStreamHasOperationMarkedInFlight(stream) === false &&
+    WritableStreamCloseQueuedOrInFlight(stream) === false) {
+    const backpressure = WritableStreamDefaultControllerGetBackpressure(controller);
+    WritableStreamUpdateBackpressure(stream, backpressure);
+  }
+}
+
 function WritableStreamDefaultControllerWrite(controller, chunk, chunkSize) {
   try {
     EnqueueValueWithSize(controller, chunk, chunkSize);
@@ -735,6 +753,8 @@ function WritableStreamDefaultControllerWrite(controller, chunk, chunkSize) {
     return;
   }
 
+  controller._releaseBackpressure = false;
+
   const stream = controller._stream;
   if (WritableStreamCloseQueuedOrInFlight(stream) === false && stream._state === 'writable') {
     const backpressure = WritableStreamDefaultControllerGetBackpressure(controller);