stream: use bitmap in readable state

lib/internal/streams/readable.js

@@ -83,6 +83,75 @@
 
 const { errorOrDestroy } = destroyImpl;
 
+const kObjectMode = 1 << 0;
+const kEnded = 1 << 1;
+const kEndEmitted = 1 << 2;
+const kReading = 1 << 3;
+const kConstructed = 1 << 4;
+const kSync = 1 << 5;
+const kNeedReadable = 1 << 6;
+const kEmittedReadable = 1 << 7;
+const kReadableListening = 1 << 8;
+const kResumeScheduled = 1 << 9;
+const kErrorEmitted = 1 << 10;
+const kEmitClose = 1 << 11;
+const kAutoDestroy = 1 << 12;
+const kDestroyed = 1 << 13;
+const kClosed = 1 << 14;
+const kCloseEmitted = 1 << 15;
+const kMultiAwaitDrain = 1 << 16;
+const kReadingMore = 1 << 17;
+const kDataEmitted = 1 << 18;
+
+// TODO(benjamingr) it is likely slower to do it this way than with free functions
+function makeBitMapDescriptor(bit) {
+  return {
+    enumerable: false,
+    get() { return (this.state & bit) !== 0; },
+    set(value) {
+      if (value) this.state |= bit;
+      else this.state &= ~bit;
+    },
+  };
+}
+ObjectDefineProperties(ReadableState.prototype, {
+  objectMode: makeBitMapDescriptor(kObjectMode),
+  ended: makeBitMapDescriptor(kEnded),
+  endEmitted: makeBitMapDescriptor(kEndEmitted),
+  reading: makeBitMapDescriptor(kReading),
+  // Stream is still being constructed and cannot be
+  // destroyed until construction finished or failed.
+  // Async construction is opt in, therefore we start as
+  // constructed.
+  constructed: makeBitMapDescriptor(kConstructed),
+  // A flag to be able to tell if the event 'readable'/'data' is emitted
+  // immediately, or on a later tick.  We set this to true at first, because
+  // any actions that shouldn't happen until "later" should generally also
+  // not happen before the first read call.
+  sync: makeBitMapDescriptor(kSync),
+  // Whenever we return null, then we set a flag to say
+  // that we're awaiting a 'readable' event emission.
+  needReadable: makeBitMapDescriptor(kNeedReadable),
+  emittedReadable: makeBitMapDescriptor(kEmittedReadable),
+  readableListening: makeBitMapDescriptor(kReadableListening),
+  resumeScheduled: makeBitMapDescriptor(kResumeScheduled),
+  // True if the error was already emitted and should not be thrown again.
+  errorEmitted: makeBitMapDescriptor(kErrorEmitted),
+  emitClose: makeBitMapDescriptor(kEmitClose),
+  autoDestroy: makeBitMapDescriptor(kAutoDestroy),
+  // Has it been destroyed.
+  destroyed: makeBitMapDescriptor(kDestroyed),
+  // Indicates whether the stream has finished destroying.
+  closed: makeBitMapDescriptor(kClosed),
+  // True if close has been emitted or would have been emitted
+  // depending on emitClose.
+  closeEmitted: makeBitMapDescriptor(kCloseEmitted),
+  multiAwaitDrain: makeBitMapDescriptor(kMultiAwaitDrain),
+  // If true, a maybeReadMore has been scheduled.
+  readingMore: makeBitMapDescriptor(kReadingMore),
+  dataEmitted: makeBitMapDescriptor(kDataEmitted),
+});
+
 function ReadableState(options, stream, isDuplex) {
   // Duplex streams are both readable and writable, but share
   // the same options object.
@@ -92,13 +161,15 @@
   if (typeof isDuplex !== 'boolean')
     isDuplex = stream instanceof Stream.Duplex;
 
+  // Bit map field to store ReadableState more effciently with 1 bit per field
+  // instead of a V8 slot per field.
+  this.state = kEmitClose | kAutoDestroy | kConstructed | kSync;
   // Object stream flag. Used to make read(n) ignore n and to
   // make all the buffer merging and length checks go away.
-  this.objectMode = !!(options && options.objectMode);
+  if (options && options.objectMode) this.state |= kObjectMode;
 
-  if (isDuplex)
-    this.objectMode = this.objectMode ||
-      !!(options && options.readableObjectMode);
+  if (isDuplex && options && options.readableObjectMode)
+    this.state |= options.readableObjectMode;
 
   // The point at which it stops calling _read() to fill the buffer
   // Note: 0 is a valid value, means "don't call _read preemptively ever"
@@ -113,54 +184,22 @@
   this.length = 0;
   this.pipes = [];
   this.flowing = null;
-  this.ended = false;
-  this.endEmitted = false;
-  this.reading = false;
 
-  // Stream is still being constructed and cannot be
-  // destroyed until construction finished or failed.
-  // Async construction is opt in, therefore we start as
-  // constructed.
-  this.constructed = true;
-
-  // A flag to be able to tell if the event 'readable'/'data' is emitted
-  // immediately, or on a later tick.  We set this to true at first, because
-  // any actions that shouldn't happen until "later" should generally also
-  // not happen before the first read call.
-  this.sync = true;
-
-  // Whenever we return null, then we set a flag to say
-  // that we're awaiting a 'readable' event emission.
-  this.needReadable = false;
-  this.emittedReadable = false;
-  this.readableListening = false;
-  this.resumeScheduled = false;
   this[kPaused] = null;
 
-  // True if the error was already emitted and should not be thrown again.
-  this.errorEmitted = false;
-
   // Should close be emitted on destroy. Defaults to true.
-  this.emitClose = !options || options.emitClose !== false;
+  if (options && options.emitClose === false) this.state &= ~kEmitClose;
 
   // Should .destroy() be called after 'end' (and potentially 'finish').
-  this.autoDestroy = !options || options.autoDestroy !== false;
+  if (options && options.autoDestroy === false) this.state &= ~kAutoDestroy;
 
-  // Has it been destroyed.
-  this.destroyed = false;
 
   // Indicates whether the stream has errored. When true no further
   // _read calls, 'data' or 'readable' events should occur. This is needed
   // since when autoDestroy is disabled we need a way to tell whether the
   // stream has failed.
   this.errored = null;
 
-  // Indicates whether the stream has finished destroying.
-  this.closed = false;
-
-  // True if close has been emitted or would have been emitted
-  // depending on emitClose.
-  this.closeEmitted = false;
 
   // Crypto is kind of old and crusty.  Historically, its default string
   // encoding is 'binary' so we have to make this configurable.
@@ -177,12 +216,6 @@
   // Ref the piped dest which we need a drain event on it
   // type: null | Writable | Set<Writable>.
   this.awaitDrainWriters = null;
-  this.multiAwaitDrain = false;
-
-  // If true, a maybeReadMore has been scheduled.
-  this.readingMore = false;
-
-  this.dataEmitted = false;
 
   this.decoder = null;
   this.encoding = null;
@@ -263,7 +296,7 @@
   const state = stream._readableState;
 
   let err;
-  if (!state.objectMode) {
+  if ((state.state & kObjectMode) === 0) {
     if (typeof chunk === 'string') {
       encoding = encoding || state.defaultEncoding;
       if (state.encoding !== encoding) {
@@ -290,11 +323,11 @@
   if (err) {
     errorOrDestroy(stream, err);
   } else if (chunk === null) {
-    state.reading = false;
+    state.state &= ~kReading;
     onEofChunk(stream, state);
-  } else if (state.objectMode || (chunk && chunk.length > 0)) {
+  } else if (((state.state & kObjectMode) !== 0) || (chunk && chunk.length > 0)) {
     if (addToFront) {
-      if (state.endEmitted)
+      if ((state.state & kEndEmitted) !== 0)
         errorOrDestroy(stream, new ERR_STREAM_UNSHIFT_AFTER_END_EVENT());
       else if (state.destroyed || state.errored)
         return false;
@@ -305,7 +338,7 @@
     } else if (state.destroyed || state.errored) {
       return false;
     } else {
-      state.reading = false;
+      state.state &= ~kReading;
       if (state.decoder && !encoding) {
         chunk = state.decoder.write(chunk);
         if (state.objectMode || chunk.length !== 0)
@@ -317,7 +350,7 @@
       }
     }
   } else if (!addToFront) {
-    state.reading = false;
+    state.state &= ~kReading;
     maybeReadMore(stream, state);
   }
 
@@ -333,7 +366,7 @@
       stream.listenerCount('data') > 0) {
     // Use the guard to avoid creating `Set()` repeatedly
     // when we have multiple pipes.
-    if (state.multiAwaitDrain) {
+    if ((state.state & kMultiAwaitDrain) !== 0) {
       state.awaitDrainWriters.clear();
     } else {
       state.awaitDrainWriters = null;
@@ -349,7 +382,7 @@
     else
       state.buffer.push(chunk);
 
-    if (state.needReadable)
+    if ((state.state & kNeedReadable) !== 0)
       emitReadable(stream);
   }
   maybeReadMore(stream, state);
@@ -404,7 +437,7 @@
 function howMuchToRead(n, state) {
   if (n <= 0 || (state.length === 0 && state.ended))
     return 0;
-  if (state.objectMode)
+  if ((state.state & kObjectMode !== 0))
     return 1;
   if (NumberIsNaN(n)) {
     // Only flow one buffer at a time.
@@ -435,9 +468,9 @@
     state.highWaterMark = computeNewHighWaterMark(n);
 
   if (n !== 0)
-    state.emittedReadable = false;
-
-  // If we're doing read(0) to trigger a readable event, but we
+    state.state &= ~kEmittedReadable;
+  
+    // If we're doing read(0) to trigger a readable event, but we
   // already have a bunch of data in the buffer, then just trigger
   // the 'readable' event and move on.
   if (n === 0 &&
@@ -486,7 +519,7 @@
   // 3. Actually pull the requested chunks out of the buffer and return.
 
   // if we need a readable event, then we need to do some reading.
-  let doRead = state.needReadable;
+  let doRead = (state.state & kNeedReadable) !== 0;
   debug('need readable', doRead);
 
   // If we currently have less than the highWaterMark, then also read some.
@@ -504,20 +537,19 @@
     debug('reading, ended or constructing', doRead);
   } else if (doRead) {
     debug('do read');
-    state.reading = true;
-    state.sync = true;
+    state.state |= kReading | kSync;
     // If the length is currently zero, then we *need* a readable event.
     if (state.length === 0)
-      state.needReadable = true;
+      state.state |= kNeedReadable;
 
     // Call internal read method
     try {
       this._read(state.highWaterMark);
     } catch (err) {
       errorOrDestroy(this, err);
     }
+    state.state &= ~kSync;
 
-    state.sync = false;
     // If _read pushed data synchronously, then `reading` will be false,
     // and we need to re-evaluate how much data we can return to the user.
     if (!state.reading)