src/vs/workbench/contrib/mergeEditor/browser/utils.ts/ReentrancyBarrier/runExclusivelyOrThrow
class ReentrancyBarrier:	public runExclusivelyOrThrow(fn: () => void): void {
		if (this._isActive) {
			throw new BugIndicatingError();
		}
		this._isActive = true;
		try {
			fn();
		} finally {
			this._isActive = false;
		}
	}