github.com/fiatjaf/generic-ristretto@v0.0.1/z/mmap_unix.go (about)

     1  // +build !windows,!darwin,!plan9,!linux
     2  
     3  /*
     4   * Copyright 2019 Dgraph Labs, Inc. and Contributors
     5   *
     6   * Licensed under the Apache License, Version 2.0 (the "License");
     7   * you may not use this file except in compliance with the License.
     8   * You may obtain a copy of the License at
     9   *
    10   *     http://www.apache.org/licenses/LICENSE-2.0
    11   *
    12   * Unless required by applicable law or agreed to in writing, software
    13   * distributed under the License is distributed on an "AS IS" BASIS,
    14   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    15   * See the License for the specific language governing permissions and
    16   * limitations under the License.
    17   */
    18  
    19  package z
    20  
    21  import (
    22  	"os"
    23  
    24  	"golang.org/x/sys/unix"
    25  )
    26  
    27  // Mmap uses the mmap system call to memory-map a file. If writable is true,
    28  // memory protection of the pages is set so that they may be written to as well.
    29  func mmap(fd *os.File, writable bool, size int64) ([]byte, error) {
    30  	mtype := unix.PROT_READ
    31  	if writable {
    32  		mtype |= unix.PROT_WRITE
    33  	}
    34  	return unix.Mmap(int(fd.Fd()), 0, int(size), mtype, unix.MAP_SHARED)
    35  }
    36  
    37  // Munmap unmaps a previously mapped slice.
    38  func munmap(b []byte) error {
    39  	return unix.Munmap(b)
    40  }
    41  
    42  // Madvise uses the madvise system call to give advise about the use of memory
    43  // when using a slice that is memory-mapped to a file. Set the readahead flag to
    44  // false if page references are expected in random order.
    45  func madvise(b []byte, readahead bool) error {
    46  	flags := unix.MADV_NORMAL
    47  	if !readahead {
    48  		flags = unix.MADV_RANDOM
    49  	}
    50  	return unix.Madvise(b, flags)
    51  }
    52  
    53  func msync(b []byte) error {
    54  	return unix.Msync(b, unix.MS_SYNC)
    55  }