github.com/zuoyebang/bitalosdb@v1.1.1-0.20240516111551-79a8c4d8ce20/internal/vfs/fd.go (about)

     1  // Copyright 2021 The Bitalosdb author(hustxrb@163.com) and other contributors.
     2  //
     3  // Licensed under the Apache License, Version 2.0 (the "License");
     4  // you may not use this file except in compliance with the License.
     5  // You may obtain a copy of the License at
     6  //
     7  //     http://www.apache.org/licenses/LICENSE-2.0
     8  //
     9  // Unless required by applicable law or agreed to in writing, software
    10  // distributed under the License is distributed on an "AS IS" BASIS,
    11  // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    12  // See the License for the specific language governing permissions and
    13  // limitations under the License.
    14  
    15  package vfs
    16  
    17  // fdGetter is an interface for a file with an Fd() method. A lot of
    18  // File related optimizations (eg. Prefetch(), WAL recycling) rely on the
    19  // existence of the Fd method to return a raw file descriptor.
    20  type fdGetter interface {
    21  	Fd() uintptr
    22  }
    23  
    24  // fdFileWrapper is a File wrapper that also exposes an Fd() method. Used to
    25  // wrap outer (wrapped) Files that could unintentionally hide the Fd() method
    26  // exposed by the inner (unwrapped) File. It effectively lets the Fd() method
    27  // bypass the outer File and go to the inner File.
    28  type fdFileWrapper struct {
    29  	File
    30  
    31  	// All methods usually pass through to File above, except for Fd(), which
    32  	// bypasses it and gets called directly on the inner file.
    33  	inner fdGetter
    34  }
    35  
    36  func (f *fdFileWrapper) Fd() uintptr {
    37  	return f.inner.Fd()
    38  }
    39  
    40  // WithFd takes an inner (unwrapped) and an outer (wrapped) vfs.File,
    41  // and returns an fdFileWrapper if the inner file has an Fd() method. Use this
    42  // method to fix the hiding of the Fd() method and the subsequent unintentional
    43  // disabling of Fd-related file optimizations.
    44  func WithFd(inner, outer File) File {
    45  	if f, ok := inner.(fdGetter); ok {
    46  		return &fdFileWrapper{
    47  			File:  outer,
    48  			inner: f,
    49  		}
    50  	}
    51  	return outer
    52  }