What are the security points in java?

Java safe points are specific moments when the JVM pauses threads to perform garbage collection to ensure that the application state is stable and reduce pause time. Safe points are typically located at method calls, loops, and synchronized block boundaries. After the JVM sends the request, the thread will be paused at the nearest safe point, then the JVM will perform garbage collection, and the thread will continue executing after the collection is completed. Optimizations include incremental garbage collection, concurrent mark scans, and biased locking to reduce pause times and avoid impacting application execution.

Java Safe Point

Java Safe Point means that the Java Virtual Machine (JVM) suspends all application threads to The specific moment at which garbage collection is performed.

The role of safe points

• Allow the JVM to perform garbage collection while the application is running
• Ensure the execution status of the application during garbage collection Does not change
• Reduce application pause time

The location of safe points

Safe points are usually located in the following scenarios:

• Method call boundaries: When a thread calls another method, safe points are inserted before and after the method call.
• Loop boundaries: Safe points are inserted when a thread enters or exits a loop.
• Synchronized block boundaries: Safe points are inserted when a thread enters or exits a synchronized block.

Safe point mechanism

When the JVM is ready for garbage collection:

• It will send a safe point request to all Application thread.
• All threads will stop execution after reaching the nearest safe point.
• JVM performs garbage collection.
• Application threads continue execution after garbage collection is completed.

Optimizing safe points

To reduce application pause time, the JVM can optimize safe points in the following ways:

• Incremental garbage collection: Break the garbage collection process into smaller increments, thereby reducing the pause time of a single safe point.
• Concurrent mark scan: Perform the garbage collection marking phase while the application is executing, thereby reducing application pause time.
• Biased lock: Avoid competing for lower lock synchronization, thereby reducing safe point waiting time.

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