One of the fundamental design decisions in an operating system is how to handle coordination between synchronous and asynchronous event handlers, especially handling the asynchronous interrupts. Interrupt synchronization is critical for real-time operating systems to increase system performance and reduce the interrupt response time. This paper proposes an interrupt synchronization lock (ISLock) technology to synchronize the interrupts without masking. Experimental evaluation shows the ISLock improves the interrupt response. We present results for a real-time embedded operating system, although the technique is applicable to both embedded and general operating systems that rely on interrupts to respond to asynchronous events.