We have learned Go pointers from the article pointers in Go. From that article, we know that, comparing to C pointers, there are many restrictions made for Go pointers. For example, Go pointers can't participate arithmetic operations, and for two arbitrary pointer types, it is very possible that their values can't be converted to each other.
The pointers explained in that article are called type-safe pointers actually. Although the restrictions on type-safe pointers really make us be able to write safe Go code with ease, they also make some obstacles to write efficient code for some scenarios.
In fact, Go also supports type-unsafe pointers, which are pointers without the restrictions made for safe pointers. Type-unsafe pointers are also called unsafe pointers in Go. Go unsafe pointers are much like C pointers, they are powerful, and also dangerous. For some cases, we can write more efficient code with the help of unsafe pointers. On the other hand, by using unsafe pointers, it is easy to write bad code which is too subtle to detect in time.
Another big risk of using unsafe pointers comes from the fact that the unsafe mechanism is not protected by the Go 1 compatibility guidelines. Code depending on unsafe pointers works today could break since a later Go version.
If you really desire the code efficient improvements by using unsafe pointers for any reason, you should not only know the above mentioned risks, but also follow the instructions written in the official Go documentation and clearly understand the effect of each unsafe pointer use, so that you can write safe Go code with unsafe pointers.
unsafe Standard Packageunsafe standard package
to use unsafe pointers.
The unsafe.Pointer type is defined as
type Pointer *ArbitraryType
Surely, it is not a usual type definition.
Here the ArbitraryType
just hints that a unsafe.Pointer value can be converted
to any safe pointer values in Go (and vice versa).
In other words, unsafe.Pointer is like the void* in C language.
Go unsafe pointers mean the types
whose underlying types are unsafe.Pointer.
The zero values of unsafe pointers are also represented with
the predeclared identifier nil.
unsafe standard package has already provided three functions.
func Alignof(variable ArbitraryType) uintptr,
which is used to get the address alignment of a value.
Please notes, the aligns for struct-field values and non-field values
of the same type may be different, though for the standard
Go compiler, they are always the same. For the gccgo compiler, they may be different.
func Offsetof(selector ArbitraryType) uintptr,
which is used to get the address offset of a field in a struct value.
The offset is relative to the address of the struct value.
The return results should be always the same for the same corresponding
field of values of the same struct type in the same program.
func Sizeof(variable ArbitraryType) uintptr,
which is used to get the size of a value
(a.k.a., the size of the type of the value).
The return results should be always the same
for all values of the same type in the same program.
uintptr. Below we will learn that uintptr values
can be converted to unsafe pointers (and vice versa).
uintptr.
unsafe.Offsetof function
must the struct field selector form value.field.
The selector may denote an embedded field, but the field must be reachable
without implicit pointer indirections.
package main
import "fmt"
import "unsafe"
func main() {
var x struct {
a int64
b bool
c string
}
const M, N = unsafe.Sizeof(x.c), unsafe.Sizeof(x)
fmt.Println(M, N) // 16 32
fmt.Println(unsafe.Alignof(x.a)) // 8
fmt.Println(unsafe.Alignof(x.b)) // 1
fmt.Println(unsafe.Alignof(x.c)) // 8
fmt.Println(unsafe.Offsetof(x.a)) // 0
fmt.Println(unsafe.Offsetof(x.b)) // 8
fmt.Println(unsafe.Offsetof(x.c)) // 16
}
An example which demonstrates the last note mentioned above.
package main
import "fmt"
import "unsafe"
func main() {
type T struct {
c string
}
type S struct {
b bool
}
var x struct {
a int64
*S
T
}
fmt.Println(unsafe.Offsetof(x.a)) // 0
fmt.Println(unsafe.Offsetof(x.S)) // 8
fmt.Println(unsafe.Offsetof(x.T)) // 16
// This line compiles, for c can be reached
// without implicit pointer indirections.
fmt.Println(unsafe.Offsetof(x.c)) // 16
// This line doesn't compile, for b must be
// reached with the implicit pointer field S.
//fmt.Println(unsafe.Offsetof(x.b)) // error
// This line compiles. However, it prints
// the offset of field b in the value x.S.
fmt.Println(unsafe.Offsetof(x.S.b)) // 0
}
Please note, the print results shown in the comments are for the standard Go compiler version 1.22.n on Linux AMD64 architecture.
The three functions provided in the unsafe package don't look much dangerous.
The signatures of these functions are very
impossible to be changed in future Go 1 versions.
Rob Pike even ever made a proposal to move the three functions to elsewhere.
Most of the unsafety of the unsafe package comes from unsafe pointers.
They are as dangerous as C pointers, what is Go safe pointers always try to avoid.
unsafe package.
The new type is IntegerType, The following is its definition.
This type doesn't denote a specified type. It just represents any arbitrary integer type.
We can view it as a generic type.
type IntegerType int
func Add(ptr Pointer, len IntegerType) Pointer.
This function adds an offset to the address represented by an unsafe pointer
and return a new unsafe pointer which represents the new address.
This function partially covers the usages of the below introduced
unsafe pointer use pattern 3.
func Slice(ptr *ArbitraryType, len IntegerType) []ArbitraryType.
This function is used to derive a slice with the specified length from a safe pointer,
where ArbitraryType is the element type of the result slice.
func String(ptr *byte, len IntegerType) string.
This function is used to derive a string with the specified length from a safe byte pointer.
func StringData(str string) *byte.
This function is used to get the pointer to the underlying byte sequence of a string.
Please note, don't pass empty strings as arguments to this function.
func SliceData(slice []ArbitraryType) *ArbitraryType.
This function is used to get the pointer to the underlying element sequence of a slice.
package main
import (
"fmt"
"unsafe"
)
func main() {
a := [16]int{3: 3, 9: 9, 11: 11}
fmt.Println(a)
eleSize := int(unsafe.Sizeof(a[0]))
p9 := &a[9]
up9 := unsafe.Pointer(p9)
p3 := (*int)(unsafe.Add(up9, -6 * eleSize))
fmt.Println(*p3) // 3
s := unsafe.Slice(p9, 5)[:3]
fmt.Println(s) // [9 0 11]
fmt.Println(len(s), cap(s)) // 3 5
t := unsafe.Slice((*int)(nil), 0)
fmt.Println(t == nil) // true
// The following two calls are dangerous.
// They make the results reference
// unknown memory blocks.
_ = unsafe.Add(up9, 7 * eleSize)
_ = unsafe.Slice(p9, 8)
}
The following two functions may be used to do conversions between strings and byte slices, in type unsafe manners. Comparing with type safe manners, the type unsafe manners don't duplicate underlying byte sequences of strings and byte slices, so they are more performant.
import "unsafe"
func String2ByteSlice(str string) []byte {
if str == "" {
return nil
}
return unsafe.Slice(unsafe.StringData(str), len(str))
}
func ByteSlice2String(bs []byte) string {
if len(bs) == 0 {
return ""
}
return unsafe.String(unsafe.SliceData(bs), len(bs))
}
By using these conversions, we can convert a safe pointer value to an arbitrary safe pointer type.
However, although these conversions are all legal at compile time, not all of them are valid (safe) at run time. These conversions defeat the memory safety the whole Go type system (except the unsafe part) tries to maintain. We must follow the instructions listed in a later section below to write valid Go code with unsafe pointers.
Before introducing the valid unsafe pointer use patterns, we need to know some facts in Go.
Each of non-nil safe and unsafe pointers references another value. However uintptr values don't reference any values, they are just plain integers, though often each of them stores an integer which can be used to represent a memory address.
Go is a language supporting automatic garbage collection. When a Go program is running, Go runtime will check which memory blocks are not used by any value any more and collect the memory allocated for these unused blocks, from time to time. Pointers play an important role in the check process. If a memory block is unreachable from (referenced by) any values still in use, then Go runtime thinks it is an unused value and it can be safely garbage collected.
As uintptr values are integers, they can participate arithmetic operations.
The example in the next subsection shows the differences between pointers and uintptr values.
At run time, the garbage collector may run at an uncertain time, and each garbage collection process may last an uncertain duration. So when a memory block becomes unused, it may be collected at an uncertain time.
For example:import "unsafe"
// Assume createInt will not be inlined.
//go:noinline
func createInt() *int {
return new(int)
}
func foo() {
p0, y, z := createInt(), createInt(), createInt()
var p1 = unsafe.Pointer(y)
var p2 = uintptr(unsafe.Pointer(z))
// At the time, even if the address of the int
// value referenced by z is still stored in p2,
// the int value has already become unused, so
// garbage collector can collect the memory
// allocated for it now. On the other hand, the
// int values referenced by p0 and p1 are still
// in use.
// uintptr can participate arithmetic operations.
p2 += 2; p2--; p2--
*p0 = 1 // okay
*(*int)(p1) = 2 // okay
*(*int)(unsafe.Pointer(p2)) = 3 // dangerous!
}
In the above example, the fact that value p2 is still in use can't guarantee
that the memory block ever hosting the int value referenced by z has not been garbage collected yet.
In other words, when *(*int)(unsafe.Pointer(p2)) = 3 is executed, the memory block may be collected, or not.
It is dangerous to dereference the address stored in value p2 to an int value,
for it is possible that the memory block has been already reallocated for another value (even for another program).
Please read the article memory blocks for details (see the end of the hyperlinked section). Here, we should just know that when the size of the stack of a goroutine changes, the memory blocks allocated on the stack will be moved. In other words, the addresses of the values hosted on these memory blocks will change.
In the following example, the fact value t is still in use
can't guarantee that the values referenced by value t.y are still in use.
type T struct {
x int
y *[1<<23]byte
}
func bar() {
t := T{y: new([1<<23]byte)}
p := uintptr(unsafe.Pointer(&t.y[0]))
... // use T.x and T.y
// A smart compiler can detect that the value
// t.y will never be used again and think the
// memory block hosting t.y can be collected now.
// Using *(*byte)(unsafe.Pointer(p))) is
// dangerous here.
// Continue using value t, but only use its x field.
println(t.x)
}
*unsafe.Pointer is a general safe pointer type
Yes, *unsafe.Pointer is a safe pointer type.
Its base type is unsafe.Pointer.
As it is a safe pointer, according the conversion rules listed above,
it can be converted to unsafe.Pointer type, and vice versa.
package main
import "unsafe"
func main() {
x := 123 // of type int
p := unsafe.Pointer(&x) // of type unsafe.Pointer
pp := &p // of type *unsafe.Pointer
p = unsafe.Pointer(pp)
pp = (*unsafe.Pointer)(p)
}
The unsafe standard package documentation lists
six unsafe pointer use patterns.
Following will introduce and explain them one by one.
*T1 value to unsafe Pointer, then convert the unsafe pointer value to *T2.
As mentioned above, by using the unsafe pointer conversion rules above,
we can convert a value of *T1 to type *T2,
where T1 and T2 are two arbitrary types.
However, we should only do such conversions if the size of T1
is no smaller than T2, and only if the conversions are meaningful.
As a result, we can also achieve the conversions between
type T1 and T2 by using this pattern.
math.Float64bits function,
which converts a float64 value to an uint64 value,
without changing any bit in the float64 value.
The math.Float64frombits function does reverse conversions.
func Float64bits(f float64) uint64 {
return *(*uint64)(unsafe.Pointer(&f))
}
func Float64frombits(b uint64) float64 {
return *(*float64)(unsafe.Pointer(&b))
}
Please note, the return result of the math.Float64bits(aFloat64)
function call is different from the result of the explicit conversion
uint64(aFloat64).
[]MyString
slice to type []string, and vice versa.
The result slice and the original slice share the underlying elements.
Such conversions are impossible through safe ways,
package main
import (
"fmt"
"unsafe"
)
func main() {
type MyString string
ms := []MyString{"C", "C++", "Go"}
fmt.Printf("%s\n", ms) // [C C++ Go]
// ss := ([]string)(ms) // compiling error
ss := *(*[]string)(unsafe.Pointer(&ms))
ss[1] = "Zig"
fmt.Printf("%s\n", ms) // [C Zig Go]
// ms = []MyString(ss) // compiling error
ms = *(*[]MyString)(unsafe.Pointer(&ss))
// Since Go 1.17, we may also use the
// unsafe.Slice function to do the conversions.
ss = unsafe.Slice((*string)(&ms[0]), len(ms))
ms = unsafe.Slice((*MyString)(&ss[0]), len(ms))
}
unsafe.Slice function to do the conversions:
func main() {
...
ss = unsafe.Slice((*string)(&ms[0]), len(ms))
ms = unsafe.Slice((*MyString)(&ss[0]), len(ss))
}
A practice by using the pattern is to convert a byte slice, which will not be used after the conversion, to a string, as the following code shows. In this conversion, a duplication of the underlying byte sequence is avoided.
func ByteSlice2String(bs []byte) string {
return *(*string)(unsafe.Pointer(&bs))
}
This is the implementation adopted by the String method
of the Builder type supported since Go 1.10 in the
strings standard package.
The size of a byte slice is larger than a string,
and their internal structures are similar,
so the conversion is valid (for main stream Go compilers).
However, despite the implementation may be safely used in standard packages now,
it is not recommended to be used in general user code.
Since Go 1.20, in general user code, we should try to use the implementation
which uses the unsafe.String function, mentioned above in this article.
func String2ByteSlice(s string) []byte {
return *(*[]byte)(unsafe.Pointer(&s)) // dangerous!
}
In the pattern 6 section below, a valid implementation to do the same job is introduced.
Note: when using the just introduced unsafe way to convert a byte slice to a string, please make sure not to modify the bytes in the byte slice if the result string still survives.
This pattern is not very useful. Usually, we print the result uintptr values to check the memory addresses stored in them. However, there are other both safe and less verbose ways to this job. So this pattern is not much useful.
Example:package main
import "fmt"
import "unsafe"
func main() {
type T struct{a int}
var t T
fmt.Printf("%p\n", &t) // 0xc6233120a8
println(&t) // 0xc6233120a8
fmt.Printf("%x\n", uintptr(unsafe.Pointer(&t))) // c6233120a8
}
The outputted addresses might be different for each run.
package main
import "fmt"
import "unsafe"
type T struct {
x bool
y [3]int16
}
const N = unsafe.Offsetof(T{}.y)
const M = unsafe.Sizeof(T{}.y[0])
func main() {
t := T{y: [3]int16{123, 456, 789}}
p := unsafe.Pointer(&t)
// "uintptr(p)+N+M+M" is the address of t.y[2].
ty2 := (*int16)(unsafe.Pointer(uintptr(p)+N+M+M))
fmt.Println(*ty2) // 789
}
In fact, since Go 1.17, it is more recommended to use the above introduced
unsafe.Add function to do such address offset operations.
unsafe.Pointer(uintptr(p) + N + M + M)
shouldn't be split into two lines, like the following code shows.
Please read the comments in the code for the reason.
func main() {
t := T{y: [3]int16{123, 456, 789}}
p := unsafe.Pointer(&t)
// ty2 := (*int16)(unsafe.Pointer(uintptr(p)+N+M+M))
addr := uintptr(p) + N + M + M
// ... (some other operations)
// Now the t value becomes unused, its memory may be
// garbage collected at this time. So the following
// use of the address of t.y[2] may become invalid
// and dangerous!
// Another potential danger is, if some operations
// make the stack grow or shrink here, then the
// address of t might change, so that the address
// saved in addr will become invalid (fact 3).
ty2 := (*int16)(unsafe.Pointer(addr))
fmt.Println(*ty2)
}
Such bugs are very subtle and hard to detect, which is why the uses of unsafe pointers are dangerous.
The intermediate uintptr value may also participate in &^ bitwise clear operations to do address alignment,
as long as the result unsafe pointer and the original one point into the same allocated memory block.
Another detail which should be also noted is that, it is not recommended to store the end boundary of a memory block in a pointer (either safe or unsafe one). Doing this will prevent another memory block which closely follows the former memory block from being garbage collected, or crash program if that boundary address is not valid for any allocated memory blocks (depending on compiler implementations). Please read this FAQ item to get more explanations.
uintptr values as arguments of syscall.Syscall calls.// Assume this function will not inlined.
func DoSomething(addr uintptr) {
// read or write values at the passed address ...
}
The reason why the above function is dangerous is that the function itself can't guarantee the memory block at the passed argument address is not garbage collected yet. If the memory block is collected or is reallocated for other values, then the operations made in the function body are dangerous.
However, the prototype of theSyscall function in
the syscall standard package is as
func Syscall(trap, a1, a2, a3 uintptr) (r1, r2 uintptr, err Errno)
How does this function guarantee that the memory blocks at the passed addresses
a1, a2 and a3 are still not garbage
collected yet within the function internal?
The function can't guarantee this.
In fact, compilers will make the guarantee.
It is the privilege of calls to syscall.Syscall alike functions.
We can think that, compilers will automatically insert some instructions
for each of the unsafe pointer arguments who are converted to uintptr,
like the third argument in the following syscall.Syscall call,
to prevent the memory block referenced by that argument from being garbage collected or moved.
Please note that, before Go 1.15, it was okay the conversion expressions uintptr(anUnsafePointer)
act as sub-expressions of the talked arguments.
Since Go 1.15, the requirement becomes a bit stricter:
the talked arguments must present exactly as the uintptr(anUnsafePointer) form.
syscall.Syscall(SYS_READ, uintptr(fd),
uintptr(unsafe.Pointer(p)), uintptr(n))
u := uintptr(unsafe.Pointer(p))
// At this time, the value referenced by p might
// have become unused and been collected already,
// or the address of the value has changed.
syscall.Syscall(SYS_READ, uintptr(fd), u, uintptr(n))
// Arguments must be in the "uintptr(anUnsafePointer)"
// form. In fact, the call was safe before Go 1.15.
// But Go 1.15 changes the rule a bit.
syscall.Syscall(SYS_XXX, uintptr(uintptr(fd)),
uint(uintptr(unsafe.Pointer(p))), uintptr(n))
Note: this pattern also applies to the syscall.Proc.Call and syscall.LazyProc.Call methods on Windows.
Again, never use this pattern when calling other functions.
uintptr result of reflect.Value.Pointer or reflect.Value.UnsafeAddr method call to unsafe pointer
The methods Pointer and UnsafeAddr of the
Value type in the reflect standard package
both return a result of type uintptr instead of
unsafe.Pointer.
This is a deliberate design, which is to avoid converting the results of calls
(to the two methods) to any safe pointer types
without importing the unsafe standard package.
The design requires the return result of a call to either of the two methods must be converted to an unsafe pointer immediately after making the call. Otherwise, there will be small time window in which the memory block allocated at the address stored in the result might lose all references and be garbage collected.
For example, the following call is safe.p := (*int)(unsafe.Pointer(reflect.ValueOf(new(int)).Pointer()))
u := reflect.ValueOf(new(int)).Pointer()
// At this moment, the memory block at the address
// stored in u might have been collected already.
p := (*int)(unsafe.Pointer(u))
Please note that, Go 1.19 introduces a new method, reflect.Value.UnsafePointer(),
which returns a unsafe.Pointer value and is preferred over the two just mentioned functions.
That means, the old deliberate design is thought as not good now.
reflect.SliceHeader.Data or reflect.StringHeader.Data field to unsafe pointer, and the inverse.
For the same reason mentioned for the last subsection, the Data fields
of the struct type SliceHeader and StringHeader in
the reflect standard package are declared with type
uintptr instead of unsafe.Pointer.
We can convert a string pointer to a *reflect.StringHeader pointer value,
so that we can manipulate the internal of the string.
The same, we can convert a slice pointer to a *reflect.SliceHeader pointer value,
so that we can manipulate the internal of the slice.
reflect.StringHeader:
package main
import "fmt"
import "unsafe"
import "reflect"
func main() {
a := [...]byte{'G', 'o', 'l', 'a', 'n', 'g'}
s := "Java"
hdr := (*reflect.StringHeader)(unsafe.Pointer(&s))
hdr.Data = uintptr(unsafe.Pointer(&a))
hdr.Len = len(a)
fmt.Println(s) // Golang
// Now s and a share the same byte sequence, which
// makes the bytes in the string s become mutable.
a[2], a[3], a[4], a[5] = 'o', 'g', 'l', 'e'
fmt.Println(s) // Google
}
An example of using
reflect.SliceHeader:
package main
import (
"fmt"
"unsafe"
"reflect"
)
func main() {
a := [6]byte{'G', 'o', '1', '0', '1'}
bs := []byte("Golang")
hdr := (*reflect.SliceHeader)(unsafe.Pointer(&bs))
hdr.Data = uintptr(unsafe.Pointer(&a))
hdr.Len = 2
hdr.Cap = len(a)
fmt.Printf("%s\n", bs) // Go
bs = bs[:cap(bs)]
fmt.Printf("%s\n", bs) // Go101
}
In general, we should only get a
*reflect.StringHeader pointer value from an actual (already existed) string,
or get a *reflect.SliceHeader pointer value from an actual (already existed) slice.
We shouldn't do the contrary, such as creating a string from a new allocated StringHeader,
or creating a slice from a new allocated SliceHeader.
For example, the following code is dangerous.
var hdr reflect.StringHeader
hdr.Data = uintptr(unsafe.Pointer(new([5]byte)))
// Now the just allocated byte array has lose all
// references and it can be garbage collected now.
hdr.Len = 5
s := *(*string)(unsafe.Pointer(&hdr)) // dangerous!
The following is an example which shows how to convert a string to a byte slice, by using the unsafe way. Different from the safe conversion from a string to a byte slice, the unsafe way doesn't allocate a new underlying byte sequence for the result slice in each conversion.
package main
import (
"fmt"
"reflect"
"strings"
"unsafe"
)
func String2ByteSlice(str string) (bs []byte) {
strHdr := (*reflect.StringHeader)(unsafe.Pointer(&str))
sliceHdr := (*reflect.SliceHeader)(unsafe.Pointer(&bs))
sliceHdr.Data = strHdr.Data
sliceHdr.Cap = strHdr.Len
sliceHdr.Len = strHdr.Len
return
}
func main() {
// str := "Golang"
// For the official standard compiler, the above
// line will make the bytes in str allocated on
// an immutable memory zone.
// So we use the following line instead.
str := strings.Join([]string{"Go", "land"}, "")
s := String2ByteSlice(str)
fmt.Printf("%s\n", s) // Goland
s[5] = 'g'
fmt.Println(str) // Golang
}
Note, when using the just introduced unsafe way to convert a string to a byte slice, please make sure not to modify the bytes in the result byte slice if the string still survives (for demonstration purpose, the above example violates this principle).
It is also possible to convert a byte slice to a string in a similar way, which is a bit safer (but a bit slower) than the way shown in pattern 1.func ByteSlice2String(bs []byte) (str string) {
sliceHdr := (*reflect.SliceHeader)(unsafe.Pointer(&bs))
strHdr := (*reflect.StringHeader)(unsafe.Pointer(&str))
strHdr.Data = sliceHdr.Data
strHdr.Len = sliceHdr.Len
return
}
Similarly, please make sure not to modify the bytes in the argument byte slice if the result string still survives.
BTW, let's view a bad example which violates the principle of pattern 3 (the example is borrowed from one slack comment posted by Bryan C. Mills):package main
import (
"fmt"
"reflect"
"unsafe"
)
func Example_Bad() *byte {
var str = "godoc"
hdr := (*reflect.StringHeader)(unsafe.Pointer(&str))
pbyte := (*byte)(unsafe.Pointer(hdr.Data + 2))
return pbyte // *pbyte == 'd'
}
func main() {
fmt.Println(string(*Example_Bad()))
}
func Example_Good1() *byte {
var str = "godoc"
hdr := (*reflect.StringHeader)(unsafe.Pointer(&str))
pbyte := (*byte)(unsafe.Pointer(
uintptr(unsafe.Pointer(hdr.Data)) + 2))
return pbyte
}
// Works since Go 1.17.
func Example_Good2() *byte {
var str = "godoc"
hdr := (*reflect.StringHeader)(unsafe.Pointer(&str))
pbyte := (*byte)(unsafe.Add(unsafe.Pointer(hdr.Data), 2))
return pbyte
}
Tricky? Yes.
The docs
of the SliceHeader and StringHeader types in the
reflect standard package are similar in that
they say the representations of the two struct types may change in a later release.
So the above valid examples using the two types may become invalid even if the unsafe rules keep unchanged.
Fortunately, at present (Go 1.22), the two available mainstream Go compilers (the standard Go compiler and the gccgo compiler)
both recognize the representations of the two types declared in the reflect standard package.
The Go core development team also realized that the two types are inconvenient and error-prone,
so the two types have been not recommended any more since Go 1.20 and they have been deprecated since Go 1.21.
Instead, we should try to use the unsafe.String, unsafe.StringData,
unsafe.Slice and unsafe.SliceData functions described earlier in this article.
From the above contents, we know that, for some cases, the unsafe mechanism can help us write more efficient Go code. However, it is very easy to introduce some subtle bugs which have very low possibilities to produce when using the unsafe mechanism. A program with these bugs may run well for a long time, but suddenly behave abnormally and even crash at a later time. Such bugs are very hard to detect and debug.
We should only use the unsafe mechanism when we have to, and we must use it with extreme care. In particular, we should follow the instructions described above.
And again, we should aware that the unsafe mechanism introduced above may change and even become invalid totally in later Go versions, though no evidences this will happen soon. If the unsafe mechanism rules change, the above introduced valid unsafe pointer use patterns may become invalid. So please keep it easy to switch back to the safe implementations for you code depending on the unsafe mechanism.
In the end, it is worth mentioning that a dynamic analysis compiler option
-gcflags=all=-d=checkptr is supported since Go Toolchain 1.14
(it is recommended to use this option on Windows with Go Toolchain 1.15+).
When this option is used, some (but not all) incorrect unsafe pointer uses will be detected at run time.
Once such an incorrect use is detected, a panic will occur.
Thanks to Matthew Dempsky for implementing this great feature!
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reflect standard package.sync standard package.sync/atomic standard package.