compromise between code safety and speed

src/Terminal.ts

@@ -1198,17 +1198,13 @@ export class Terminal extends EventEmitter implements ITerminal, IDisposable, II
 
     if (this.buffer.scrollTop === 0) {
       // Determine whether the buffer is going to be trimmed after insertion.
-      const willBufferBeTrimmed = this.buffer.lines.pushWouldTrim();
+      const willBufferBeTrimmed = this.buffer.lines.isFull();
 
       // Insert the line using the fastest method
       if (bottomRow === this.buffer.lines.length - 1) {
         if (useRecycling) {
           if (willBufferBeTrimmed) {
-            // push would trim the oldest line in the ringbuffer
+            this.buffer.lines.recycle().copyFrom(newLine);
-            // therefore we can recycle it here as the new line
-            const recycled = this.buffer.lines.get(0);
-            recycled.copyFrom(newLine);
-            this.buffer.lines.push(recycled);
           } else {
             this.buffer.lines.push(newLine.clone());
           }

src/common/CircularList.ts

@@ -98,10 +98,24 @@ export class CircularList<T> extends EventEmitter implements ICircularList<T> {
   }
 
   /**
-   * Whether a push would trim.
+   * Advance ringbuffer index and return current element for recycling.
-   * True when the ringbuffer is full.
+   * Note: If the ringbuffer is not full this method will return undefined,
+   * Either precheck with isFull() or handle the undefined return value accordingly.
    */
-  public pushWouldTrim(): boolean {
+  public recycle(): T | undefined {
+    if (this._length === this._maxLength) {
+      this._startIndex = ++this._startIndex % this._maxLength;
+      this.emit('trim', 1);
+    } else {
+      this._length++;
+    }
+    return this._array[this._getCyclicIndex(this._length - 1)];
+  }
+
+  /**
+   * Ringbuffer is at max length.
+   */
+  public isFull(): boolean {
     return this._length === this._maxLength;
   }
 

src/common/Types.ts

@@ -28,7 +28,8 @@ export interface ICircularList<T> extends IEventEmitter {
   get(index: number): T | undefined;
   set(index: number, value: T): void;
   push(value: T): void;
-  pushWouldTrim(): boolean;
+  recycle(): T | undefined;
+  isFull(): boolean;
   pop(): T | undefined;
   splice(start: number, deleteCount: number, ...items: T[]): void;
   trimStart(count: number): void;