some buffer handling optimizations

src/common/Types.d.ts

@@ -205,7 +205,8 @@ export interface IBufferLine {
   insertCells(pos: number, n: number, ch: ICellData, eraseAttr?: IAttributeData): void;
   deleteCells(pos: number, n: number, fill: ICellData, eraseAttr?: IAttributeData): void;
   replaceCells(start: number, end: number, fill: ICellData, eraseAttr?: IAttributeData, respectProtect?: boolean): void;
-  resize(cols: number, fill: ICellData): void;
+  resize(cols: number, fill: ICellData): boolean;
+  cleanupMemory(): number;
   fill(fillCellData: ICellData, respectProtect?: boolean): void;
   copyFrom(line: IBufferLine): void;
   clone(): IBufferLine;

src/common/buffer/Buffer.ts

@@ -14,6 +14,7 @@ import { Marker } from 'common/buffer/Marker';
 import { IOptionsService, IBufferService } from 'common/services/Services';
 import { DEFAULT_CHARSET } from 'common/data/Charsets';
 import { ExtendedAttrs } from 'common/buffer/AttributeData';
+import { DebouncedIdleTask } from 'common/TaskQueue';
 
 export const MAX_BUFFER_SIZE = 4294967295; // 2^32 - 1
 
@@ -151,6 +152,9 @@ export class Buffer implements IBuffer {
     // store reference to null cell with default attrs
     const nullCell = this.getNullCell(DEFAULT_ATTR_DATA);
 
+    // defer memory cleanup of bufferlines
+    let needsCleanup = 0;
+
     // Increase max length if needed before adjustments to allow space to fill
     // as required.
     const newMaxLength = this._getCorrectBufferLength(newRows);
@@ -164,7 +168,8 @@ export class Buffer implements IBuffer {
       // Deal with columns increasing (reducing needs to happen after reflow)
       if (this._cols < newCols) {
         for (let i = 0; i < this.lines.length; i++) {
-          this.lines.get(i)!.resize(newCols, nullCell);
+          // +boolean for fast 0 or 1 conversion
+          needsCleanup |= +this.lines.get(i)!.resize(newCols, nullCell);
         }
       }
 
@@ -243,13 +248,35 @@ export class Buffer implements IBuffer {
       // Trim the end of the line off if cols shrunk
       if (this._cols > newCols) {
         for (let i = 0; i < this.lines.length; i++) {
-          this.lines.get(i)!.resize(newCols, nullCell);
+          // +boolean for fast 0 or 1 conversion
+          needsCleanup |= +this.lines.get(i)!.resize(newCols, nullCell);
         }
       }
     }
 
     this._cols = newCols;
     this._rows = newRows;
+
+    if (needsCleanup) {
+      this._memoryCleanupTask.set(() => this._cleanupMemory());
+    } else {
+      // FIXME: DebouncedIdleTask has no clear method?
+      this._memoryCleanupTask.set(() => {});
+    }
+  }
+
+  private _memoryCleanupTask: DebouncedIdleTask = new DebouncedIdleTask();
+
+  private _cleanupMemory(): void {
+    let counted = 0;
+    for (let i = 0; i < this.lines.length; i++) {
+      counted += this.lines.get(i)!.cleanupMemory();
+      // throttle to 5k lines
+      if (counted > 5000) {
+        this._memoryCleanupTask.set(() => this._cleanupMemory());
+        break;
+      }
+    }
   }
 
   private get _isReflowEnabled(): boolean {

src/common/buffer/BufferLine.ts

@@ -40,6 +40,9 @@ export const DEFAULT_ATTR_DATA = Object.freeze(new AttributeData());
 // Work variables to avoid garbage collection
 let $startIndex = 0;
 
+/** Factor when to cleanup underlying array buffer after shrinking. */
+const CLEANUP_THRESHOLD = 2;
+
 /**
  * Typed array based bufferline implementation.
  *
@@ -333,42 +336,69 @@ export class BufferLine implements IBufferLine {
     }
   }
 
-  public resize(cols: number, fillCellData: ICellData): void {
+  /**
+   * Resize BufferLine to `cols` filling excess cells with `fillCellData`.
+   * The underlying array buffer will not change if there is still enough space
+   * to hold the new buffer line data.
+   * Returns a boolean indicating, whether a `cleanBuffer` call would free
+   * excess memory (after shrinking > CLEANUP_THRESHOLD).
+   */
+  public resize(cols: number, fillCellData: ICellData): boolean {
     if (cols === this.length) {
-      return;
+      return this._data.length * 4 * CLEANUP_THRESHOLD < this._data.buffer.byteLength;
     }
+    const uint32Cells = cols * CELL_SIZE;
     if (cols > this.length) {
-      const data = new Uint32Array(cols * CELL_SIZE);
-      if (this.length) {
-        if (cols * CELL_SIZE < this._data.length) {
-          data.set(this._data.subarray(0, cols * CELL_SIZE));
-        } else {
-          data.set(this._data);
-        }
+      if (this._data.buffer.byteLength >= uint32Cells * 4) {
+        // optimization: avoid alloc and data copy if buffer has enough room
+        this._data = new Uint32Array(this._data.buffer, 0, uint32Cells);
+      } else {
+        // slow path: new alloc and full data copy
+        const data = new Uint32Array(uint32Cells);
+        data.set(this._data);
+        this._data = data;
       }
-      this._data = data;
       for (let i = this.length; i < cols; ++i) {
         this.setCell(i, fillCellData);
       }
     } else {
-      if (cols) {
-        const data = new Uint32Array(cols * CELL_SIZE);
-        data.set(this._data.subarray(0, cols * CELL_SIZE));
-        this._data = data;
-        // Remove any cut off combined data, FIXME: repeat this for extended attrs
-        const keys = Object.keys(this._combined);
-        for (let i = 0; i < keys.length; i++) {
-          const key = parseInt(keys[i], 10);
-          if (key >= cols) {
-            delete this._combined[key];
-          }
+      // optimization: just shrink the view on existing buffer
+      this._data = this._data.subarray(0, uint32Cells);
+      // Remove any cut off combined data
+      const keys = Object.keys(this._combined);
+      for (let i = 0; i < keys.length; i++) {
+        const key = parseInt(keys[i], 10);
+        if (key >= cols) {
+          delete this._combined[key];
+        }
+      }
+      // remove any cut off extended attributes
+      const extKeys = Object.keys(this._extendedAttrs);
+      for (let i = 0; i < extKeys.length; i++) {
+        const key = parseInt(extKeys[i], 10);
+        if (key >= cols) {
+          delete this._extendedAttrs[key];
         }
-      } else {
-        this._data = new Uint32Array(0);
-        this._combined = {};
       }
     }
     this.length = cols;
+    return uint32Cells * 4 * CLEANUP_THRESHOLD < this._data.buffer.byteLength;
+  }
+
+  /**
+   * Cleanup underlying array buffer.
+   * A cleanup will be triggered if the array buffer exceeds the actual used
+   * memory by a factor of CLEANUP_THRESHOLD.
+   * Returns 0 or 1 indicating whether a cleanup happened.
+   */
+  public cleanupMemory(): number {
+    if (this._data.length * 4 * CLEANUP_THRESHOLD < this._data.buffer.byteLength) {
+      const data = new Uint32Array(this._data.length);
+      data.set(this._data);
+      this._data = data;
+      return 1;
+    }
+    return 0;
   }
 
   /** fill a line with fillCharData */