AVD Nexus_5X_API_P is already running. If that is not the case, delete the files at C:\Users\2822878.android\avd/Nexus_5X_API_P.avd/*.lock and try again. 大概就是已经由一个模拟机在运行了，但是找不到模拟机。这时候就按提示去删除那个.lock文件就行，是一个文件夹。删除后在重新启动模拟器就行，完美解决。
