• Discovering and exploring mmap using Go
• But how, exactly, databases use mmap?

https://100go.co/

• runtime/map.go
• Some insights on Maps in Golang
• Memory Allocation and Performance in Golang Maps

• Go CPU profiler 内幕
• The Busy Developer's Guide to Go Profiling, Tracing and Observability

Reflection

Overview

• interface values is composed of (value, type)
• Reflection is a type of meta programming
• any interface values can be boxed into reflect.Value and reflect.Type

Laws of Reflection

1. Reflection goes from interface value to reflection object.

2. Reflection goes from reflection object to interface value.

3. To modify a reflection object, the value must be settable.

func (v Value) CanSet() bool
    CanSet reports whether the value of v can be changed. A Value can be
    changed only if it is addressable and was not obtained by the use of
    unexported struct fields. If CanSet returns false, calling Value.Set or any
    type-specific setter (e.g., Value.SetBool, Value.SetInt) will panic.

• addressable: need to be pointer variable

Kind

Although there are infinitely many types, there are only a finite number of kinds of type: the basic types Bool, String and all the numbers; the aggregate types Array and Struct, the reference types Chan, Func, Ptr, Slice and Map; interface types; and finally Invalid, meaning no value at all (The zero value of a reflect.Value has kind Invalid).

Reference

• The Go Blog: The Laws of Reflection
• Go (Golang) Reflection Tutorial

https://andrestc.com/post/go-memory-allocation-pt1/

Interview Questions

Data structure

1. 如果range over slice時對slice作改動，是否會改動slice ?
   range over slice will copy the original value.

2. how to compare 2 struct value ?
   reflect.DeepEqual

3. how to verify that struct actually implement a Interface ?
   var _ Interface = (*Struct_Should_Implement)(nil)

4. convert []byte to string 是否會造成 copy ?

   • yes
   • string is immutable but []byte is mutable

5. Modifying map while iterating over it ?

   • unpredictable
   • If a map entry is created during iteration, that entry may be produced during the iteration or may be skipped.
   • If a map entry that has not yet been reached is removed during iteration, the corresponding iteration value will not be produced.

6. How to check if a slice is sorted ?

   • sort.IsSorted()
   • sort.SliceIsSorted(), passing a less()

7. marshal json what is the result ?

type J struct {
	a string 
	b string `json:"B"`
	C string
	D string `json:"DD"`
}
	j := J{
		a: "1",
                 b: "2",
		C: "3",
		D: "4",
	}
	fmt.Printf("j = %+v\n", j) 

8. make vs new

   • both for memory allocation
   • new will allocate the zero value of type
   • make can only allocate map, slice, chan

9. can we address the map ?

   • map is not addressable
   • when hash table is reorganized, the address will change.

   m := make(map[string]int)
   fmt.Println(&m["qcrao"])
   // cannot take the address of m["qcrao"]

10. use case of tag

    • json marshall unmarshal
    • db: sqlx column mapping
    • form: gin validation for form
    • binding: gin binding for validation

11. fmt.Printf with %v %+v %#v

type animal struct {
	name string
	age  int
}

a := animal{name: "cat", age: 2}
fmt.Printf("%v\n", a) // {cat 2}
fmt.Printf("%+v\n", a) // {name:cat age:2}
fmt.Printf("%#v\n", a) // main.animal{name:"cat", age:2}

Functions

1. the execution order of import, const, var, init(), main()
   import –> const –> var –>init()–>main()

Concurrency

1. Channel deadlock的情況
   • read from nil channel
   • write to full channel
   • write to closed channel
   • all grouting blocked
2. 讀closed channel 的行為?
   • 一直讀到 zero value
   • 不會deadlock
   • 解決: 把原chan 設為 nil

Concurrency control

1. use wait group to wait for multiple goroutines returns
2. use channel to block channel sender or channel receiver
3. use channel if we need specific order of goroutine execution
4. pass context within chain of goroutine to control / cancel .
5. use select to organize multiple channels

Mutex

Design Pattern

Internals

Channel

Map

1. map is hmap struct with pointer buckets to buckets array of 2^B buckets.
2. bucket is bmap struct with 8 buckets, each bucket stores an key value pair

Web

1. Graceful shutdown
   1. start a goroutine for server.listenAndServe() in background
   2. main thread blocked and listen to os termination signal (syscall.SIGTERM )
   3. if received os signal, use context with timeout and call server to shutdown.

Ref

• Go 语言问题集(Go Questions)
• [吐血整理]超全golang面试题合集+golang学习指南+golang知识图谱+成长路线
• Go常见面试题【由浅入深】2022版
• 你遇到过哪些高质量的 Go 语言面试题？
• Golang面试问题汇总
• GO語言面試系列:（二）常規性Golang面試題解析
• 34 Go Interview Questions To Crack In 2020

• Dave Cheney: Building a high performance JSON parser
• Surprises and Gotchas When Working With JSON
• https://medium.com/geekculture/my-golang-json-evaluation-20a9ca6ef79c
• https://www.cnblogs.com/88223100/p/Which-is-the-strongest-third-party-package-for-Go-JSON.html
• Speeding up Go's builtin JSON encoder up to 55% for large arrays of objects