89 lines
1.8 KiB
Text
89 lines
1.8 KiB
Text
low-level
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Лекция 10
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Короткий Фёдор
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* Low Level Programming
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* package unsafe
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import "unsafe"
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fmt.Println(unsafe.Sizeof(float64(0))) // "8"
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- `unsafe` выглядит как обычный пакет
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- Но реализован в компиляторе
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* package unsafe
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type Pointer *ArbitraryType
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- Два преобразования
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*T -> unsafe.Pointer
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unsafe.Pointer -> *T
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- `unsafe.Pointer` - это _настоящий_ `void*`
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func Float64bits(f float64) uint64 {
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return *(*uint64)(unsafe.Pointer(&f))
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}
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* unsafe.Pointer
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.code unsafeptr/main.go /var/,/42/
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Действия с указателями дожны выполняться *атомарно*.
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.code unsafeptr/main.go /\+wrong/,/\-wrong/
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Иначе сборщик мусора освободит память используемого объекта.
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pT := uintptr(unsafe.Pointer(new(T))) // NOTE: wrong!
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* unsafe tricks
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// A Builder is used to efficiently build a string using Write methods.
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// It minimizes memory copying. The zero value is ready to use.
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// Do not copy a non-zero Builder.
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type Builder struct {
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buf []byte
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}
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// String returns the accumulated string.
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func (b *Builder) String() string {
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return *(*string)(unsafe.Pointer(&b.buf))
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}
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// *-----*-----*-----*
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// * ptr * len * cap * // []byte
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// *-----*-----*-----*
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//
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// *-----*-----*
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// * ptr * len * // string
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// *-----*-----*
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* cgo
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.code bzip/bzip2.c /include/,/^}/
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* cgo
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.code bzip/bzip2.go /package/,/import/
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.code bzip/bzip2.go /type writer/,/^}/
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* cgo
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.code bzip/bzip2.go /type writer/,/^}/
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.code bzip/bzip2.go /func NewWriter/,/^}/
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* cgo
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.code bzip/bzip2.go /func .* Write/,/^}/
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* syscall
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- syscall заморожен
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- x/sys/unix содержит актуальные реализации системных вызовов
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