sysvshm_unix.go

     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  }
    52
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