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sysvshm_unix.go (1456B)

      1 // Copyright 2021 The Go Authors. All rights reserved.
      2 // Use of this source code is governed by a BSD-style
      3 // license that can be found in the LICENSE file.
      4 
      5 //go:build (darwin && !ios) || linux || zos
      6 
      7 package unix
      8 
      9 import "unsafe"
     10 
     11 // SysvShmAttach attaches the Sysv shared memory segment associated with the
     12 // shared memory identifier id.
     13 func SysvShmAttach(id int, addr uintptr, flag int) ([]byte, error) {
     14 	addr, errno := shmat(id, addr, flag)
     15 	if errno != nil {
     16 		return nil, errno
     17 	}
     18 
     19 	// Retrieve the size of the shared memory to enable slice creation
     20 	var info SysvShmDesc
     21 
     22 	_, err := SysvShmCtl(id, IPC_STAT, &info)
     23 	if err != nil {
     24 		// release the shared memory if we can't find the size
     25 
     26 		// ignoring error from shmdt as there's nothing sensible to return here
     27 		shmdt(addr)
     28 		return nil, err
     29 	}
     30 
     31 	// Use unsafe to convert addr into a []byte.
     32 	b := unsafe.Slice((*byte)(unsafe.Pointer(addr)), int(info.Segsz))
     33 	return b, nil
     34 }
     35 
     36 // SysvShmDetach unmaps the shared memory slice returned from SysvShmAttach.
     37 //
     38 // It is not safe to use the slice after calling this function.
     39 func SysvShmDetach(data []byte) error {
     40 	if len(data) == 0 {
     41 		return EINVAL
     42 	}
     43 
     44 	return shmdt(uintptr(unsafe.Pointer(&data[0])))
     45 }
     46 
     47 // SysvShmGet returns the Sysv shared memory identifier associated with key.
     48 // If the IPC_CREAT flag is specified a new segment is created.
     49 func SysvShmGet(key, size, flag int) (id int, err error) {
     50 	return shmget(key, size, flag)
     51 }