first commit

shm.go

@@ -0,0 +1,18 @@
+// Copyright (c) 2020 Meng Huang (mhboy@outlook.com)
+// This package is licensed under a MIT license that can be found in the LICENSE file.
+
+// Package shm provides a way to use shared memory.
+package shm
+
+import (
+	"os"
+)
+
+// validSize returns the valid size.
+func validSize(size int64) int64 {
+	pageSize := int64(os.Getpagesize())
+	if size%pageSize == 0 {
+		return size
+	}
+	return (size/pageSize + 1) * pageSize
+}

shm_unix.go

@@ -0,0 +1,106 @@
+// Copyright (c) 2020 Meng Huang (mhboy@outlook.com)
+// This package is licensed under a MIT license that can be found in the LICENSE file.
+
+// +build darwin linux dragonfly freebsd netbsd openbsd
+
+package shm
+
+import (
+	"syscall"
+	"unsafe"
+)
+
+const (
+	// IPC_CREATE creates if key is nonexistent
+	IPC_CREATE = 00001000
+
+	//IPC_RMID removes identifier
+	IPC_RMID = 0
+
+	// O_RDONLY opens the file read-only.
+	O_RDONLY int = syscall.O_RDONLY
+	// O_WRONLY opens the file write-only.
+	O_WRONLY int = syscall.O_WRONLY
+	// O_RDWR opens the file read-write.
+	O_RDWR int = syscall.O_RDWR
+
+	// O_CREATE creates a new file if none exists.
+	O_CREATE int = syscall.O_CREAT
+)
+
+// GetAt calls the shmget and shmat system call.
+func GetAt(key int, size int, shmFlg int) (uintptr, []byte, error) {
+	if shmFlg == 0 {
+		shmFlg = IPC_CREATE | 0600
+	}
+	shmid, _, errno := syscall.Syscall(syscall.SYS_SHMGET, uintptr(key), uintptr(validSize(int64(size))), uintptr(shmFlg))
+	if shmid <= 0 || errno != 0 {
+		return 0, nil, syscall.Errno(errno)
+	}
+	shmaddr, _, errno := syscall.Syscall(syscall.SYS_SHMAT, shmid, 0, 0)
+	if errno != 0 {
+		Remove(shmid)
+		return 0, nil, syscall.Errno(errno)
+	}
+	var sl = struct {
+		addr uintptr
+		len  int
+		cap  int
+	}{shmaddr, size, size}
+	b := *(*[]byte)(unsafe.Pointer(&sl))
+	return shmid, b, nil
+}
+
+// Dt calls the shmdt system call.
+func Dt(b []byte) error {
+	_, _, errno := syscall.Syscall(syscall.SYS_SHMDT, uintptr(unsafe.Pointer(&b[0])), 0, 0)
+	if errno != 0 {
+		return syscall.Errno(errno)
+	}
+	return nil
+}
+
+// Remove removes the shm with the given id.
+func Remove(shmid uintptr) error {
+	_, _, errno := syscall.Syscall(syscall.SYS_SHMCTL, shmid, IPC_RMID, 0)
+	if errno != 0 {
+		return syscall.Errno(errno)
+	}
+	return nil
+}
+
+// Open returns the shm id.
+func Open(name string, oflag int, mode int) (int, error) {
+	n, err := syscall.BytePtrFromString(name)
+	if err != nil {
+		return 0, err
+	}
+	fd, _, errno := syscall.Syscall(syscall.SYS_SHM_OPEN, uintptr(unsafe.Pointer(n)), uintptr(oflag), uintptr(mode))
+	if errno != 0 {
+		return 0, errno
+	}
+	return int(fd), nil
+}
+
+// Ftruncate changes the file size of the fd.
+func Ftruncate(fd int, length int64) (err error) {
+	return syscall.Ftruncate(fd, length)
+}
+
+// Close closes the fd.
+func Close(fd int) (err error) {
+	return syscall.Close(fd)
+}
+
+// Unlink unlinks the name.
+func Unlink(name string) error {
+	n, err := syscall.BytePtrFromString(name)
+	if err != nil {
+		return err
+	}
+	_, _, errno := syscall.Syscall(syscall.SYS_SHM_UNLINK, uintptr(unsafe.Pointer(n)), 0, 0)
+	if errno != 0 {
+		return errno
+	}
+	return nil
+}