mmap.go

     1  // Copyright 2011 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  // This package is a lightly modified version of the mmap code
     6  // in github.com/google/codesearch/index.
     7  
     8  // The mmap package provides an abstraction for memory mapping files
     9  // on different platforms.
    10  package mmap
    11  
    12  import (
    13  	"os"
    14  )
    15  
    16  // Data is mmap'ed read-only data from a file.
    17  // The backing file is never closed, so Data
    18  // remains valid for the lifetime of the process.
    19  type Data struct {
    20  	f    *os.File
    21  	Data []byte
    22  }
    23  
    24  // Mmap maps the given file into memory.
    25  // The boolean result indicates whether the file was opened.
    26  // If it is true, the caller should avoid attempting
    27  // to write to the file on Windows, because Windows locks
    28  // the open file, and writes to it will fail.
    29  func Mmap(file string) (Data, bool, error) {
    30  	f, err := os.Open(file)
    31  	if err != nil {
    32  		return Data{}, false, err
    33  	}
    34  	data, err := mmapFile(f)
    35  
    36  	// Closing the file causes it not to count against this process's
    37  	// limit on open files; however, the mapping still counts against
    38  	// the system-wide limit, which is typically higher. Examples:
    39  	//
    40  	//     macOS process (sysctl kern.maxfilesperproc):  61440
    41  	//     macOS system  (sysctl kern.maxfiles):        122880
    42  	//     linux process (ulimit -n)                   1048576
    43  	//     linux system  (/proc/sys/fs/file-max)        100000
    44  	if cerr := f.Close(); cerr != nil && err == nil {
    45  		return data, true, cerr
    46  	}
    47  
    48  	// The file is still considered to be in use on Windows after
    49  	// it's closed because of the mapping.
    50  	return data, true, err
    51  }
    52
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