Decrypting the memory management and garbage collection mechanism of Go language

Go language is an efficient, safe, and concurrent programming language. The design of memory management and garbage collection mechanism is also its unique feature. This article will decrypt the memory management and garbage collection mechanism of Go language in depth.

1. Memory Management

In the Go language, memory management includes two aspects: memory allocation and memory release.

1.1 Memory allocation

In the Go language, we allocate memory through the built-in functions new and make. Among them, new returns a pointer to a newly allocated zero value, while make returns a pointer to an initialization value of the specified type and its length. We can compare the usage of new and make through the following code:

var p *int = new(int)
var v []int = make([]int, 10)
fmt.Println(*p, len(v))

Output result: 0 10

As can be seen from the above example, the memory allocated by new is a zero value of type int. The memory allocated by make is an int type slice with a length of 10.

In terms of internal implementation, Go language uses two memory allocation mechanisms: heap and stack. Among them, the heap is used to store dynamically allocated memory, and the stack is used to store statically allocated memory. Memory allocation in the stack is controlled by the program, while memory allocation in the heap is managed by the garbage collection mechanism of the Go language.

1.2 Memory Release

In Go language, memory release does not require us to operate manually, but is automatically performed by the garbage collection mechanism of Go language. When a variable is no longer used, the garbage collection mechanism will mark it as a garbage object and automatically recycle it at the appropriate time.

2. Garbage collection mechanism

The garbage collection mechanism of Go language uses a combination of mark-sweep algorithm and three-color marking algorithm to perform garbage collection.

2.1 Mark-clear algorithm

The mark-clear algorithm is a common garbage collection algorithm. Its basic idea is to mark all objects in use and then clear unmarked objects. In the implementation of Go language, the garbage collector will traverse all objects starting from the root object, mark all referenced objects as live objects, and unmarked objects as garbage objects, and finally clear all garbage objects.

The advantage of the mark-clear algorithm lies in its high efficiency and the fact that it does not need to pause the program, but its disadvantage lies in the fragmentation of memory space after recycling.

2.2 Three-color marking algorithm

In order to solve the memory fragmentation problem in the mark-clear algorithm, the garbage collection mechanism of the Go language introduces the three-color marking algorithm. In the three-color marking algorithm, the garbage collector marks all objects as white, black, or gray. Among them, white represents an object that has not been accessed, gray represents an object that has been accessed but the object it refers to has not been accessed, and black represents an object that has been accessed.

The garbage collector will traverse all objects starting from the root object, mark all referenced objects as gray, and then recursively traverse the objects referenced by these gray objects, marking the traversed objects as black. Finally, the garbage collector clears unaccessed white objects and marks gray and black objects as white.

The advantage of the three-color marking algorithm is that it can make full use of memory space and avoid the problem of memory fragmentation. But its disadvantage is that it needs to traverse the entire object graph every time it is recycled, which has a certain impact on the performance of the program.

Summary

The memory management and garbage collection mechanism of the Go language is very well designed, which allows us to allocate and release memory more conveniently when writing efficient, safe, and concurrent programs. At the same time, the implementation of the garbage collection mechanism also fully considers the memory space utilization issue, providing support for improving the performance of our program.

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