There are several garbage collection mechanisms in jvm

There are 6 common JVM garbage collection mechanisms, namely: 1. Mark-sweep algorithm; 2. Copy algorithm; 3. Mark-compression algorithm; 4. Generational collection algorithm; 5. Reference counting algorithm. ; 6. Adaptive hybrid recycling algorithm. Detailed introduction: 1. Mark-sweep algorithm, which is the most basic garbage collection algorithm. It is divided into two stages: mark stage and clear stage. In the mark stage, the garbage collector will traverse all objects and mark the surviving objects. During the cleanup phase, the garbage collector clears unmarked objects, frees their memory, and so on.

The operating system for this tutorial: Windows 10 system, DELL G3 computer.

JVM garbage collection mechanisms mainly include the following:

1. Mark-Sweep algorithm: This is the most basic garbage collection algorithm. It is divided into two phases: marking phase and clearing phase. During the marking phase, the garbage collector traverses all objects and marks the surviving objects. During the cleanup phase, the garbage collector clears unmarked objects and releases their memory. The disadvantage of this algorithm is that it will produce a large number of discontinuous memory fragments, which may lead to wasted space.

2. Copying algorithm: In order to solve the memory fragmentation problem in the mark-clear algorithm, the copying algorithm divides the memory space into two equal areas, and only uses one of them each time an area. When garbage collects, it copies live objects to another area and clears all objects in the current area. The advantage of this algorithm is that there is less memory fragmentation, but the disadvantage is that it requires twice the memory space.

3. Mark-Compact algorithm: The mark-compression algorithm is proposed to solve the memory fragmentation problem in the mark-clear algorithm. It compresses the surviving objects to one end of the memory after the mark and clear phase, and directly clears the memory outside the boundary. This algorithm avoids the problem of memory fragmentation, but the compression process requires additional time.

4. Generational collection (Generational) algorithm: The generational collection algorithm is a garbage collection algorithm based on the object survival cycle. It divides the memory into two areas: the new generation and the old generation. The young generation usually contains a large number of newly created objects, and the old generation contains long-lived objects. The garbage collector adopts different collection strategies according to the characteristics of different generations. The new generation uses the copy algorithm, and the old generation uses the mark-compression algorithm. This algorithm can improve the efficiency of garbage collection and reduce unnecessary memory cleaning.

5. Reference Counting algorithm: The reference counting algorithm tracks the life cycle of an object by maintaining a reference count for each object. When an object is referenced, its reference count is incremented by one; when the reference becomes invalid, its reference count is decremented by one. When the reference count reaches zero, it means that the object is no longer used and can be recycled. This algorithm is simple and efficient, but may have problems when dealing with circular reference problems.

6. Adaptive Hybrid recycling algorithm: The adaptive hybrid recycling algorithm is a garbage collection strategy that combines generational collection and copying algorithms. It dynamically adjusts the recycling strategy based on the proportion of surviving objects in different generations. When the proportion of surviving objects in the new generation is high, the replication algorithm is used; when the proportion of surviving objects in the old generation is high, the mark-compression algorithm is used. This algorithm can adaptively adjust the recycling strategy according to the characteristics of the application to improve the efficiency and accuracy of garbage collection.

The above are the main mechanisms of JVM garbage collection. Each of these mechanisms has its own advantages and disadvantages. It is very important to choose the appropriate garbage collection mechanism according to different application scenarios and needs. In modern JVM, a combination of multiple garbage collection mechanisms is usually used to improve the efficiency and accuracy of garbage collection to meet the performance and stability requirements of the application.

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