default.go

     1  // Copyright 2017 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  package cache
     6  
     7  import (
     8  	"fmt"
     9  	"os"
    10  	"path/filepath"
    11  	"sync"
    12  
    13  	"cmd/go/internal/base"
    14  	"cmd/go/internal/cfg"
    15  )
    16  
    17  // Default returns the default cache to use, or nil if no cache should be used.
    18  func Default() *Cache {
    19  	defaultOnce.Do(initDefaultCache)
    20  	return defaultCache
    21  }
    22  
    23  var (
    24  	defaultOnce  sync.Once
    25  	defaultCache *Cache
    26  )
    27  
    28  // cacheREADME is a message stored in a README in the cache directory.
    29  // Because the cache lives outside the normal Go trees, we leave the
    30  // README as a courtesy to explain where it came from.
    31  const cacheREADME = `This directory holds cached build artifacts from the Go build system.
    32  Run "go clean -cache" if the directory is getting too large.
    33  Run "go clean -fuzzcache" to delete the fuzz cache.
    34  See golang.org to learn more about Go.
    35  `
    36  
    37  // initDefaultCache does the work of finding the default cache
    38  // the first time Default is called.
    39  func initDefaultCache() {
    40  	dir := DefaultDir()
    41  	if dir == "off" {
    42  		if defaultDirErr != nil {
    43  			base.Fatalf("build cache is required, but could not be located: %v", defaultDirErr)
    44  		}
    45  		base.Fatalf("build cache is disabled by GOCACHE=off, but required as of Go 1.12")
    46  	}
    47  	if err := os.MkdirAll(dir, 0777); err != nil {
    48  		base.Fatalf("failed to initialize build cache at %s: %s\n", dir, err)
    49  	}
    50  	if _, err := os.Stat(filepath.Join(dir, "README")); err != nil {
    51  		// Best effort.
    52  		os.WriteFile(filepath.Join(dir, "README"), []byte(cacheREADME), 0666)
    53  	}
    54  
    55  	c, err := Open(dir)
    56  	if err != nil {
    57  		base.Fatalf("failed to initialize build cache at %s: %s\n", dir, err)
    58  	}
    59  	defaultCache = c
    60  }
    61  
    62  var (
    63  	defaultDirOnce sync.Once
    64  	defaultDir     string
    65  	defaultDirErr  error
    66  )
    67  
    68  // DefaultDir returns the effective GOCACHE setting.
    69  // It returns "off" if the cache is disabled.
    70  func DefaultDir() string {
    71  	// Save the result of the first call to DefaultDir for later use in
    72  	// initDefaultCache. cmd/go/main.go explicitly sets GOCACHE so that
    73  	// subprocesses will inherit it, but that means initDefaultCache can't
    74  	// otherwise distinguish between an explicit "off" and a UserCacheDir error.
    75  
    76  	defaultDirOnce.Do(func() {
    77  		defaultDir = cfg.Getenv("GOCACHE")
    78  		if filepath.IsAbs(defaultDir) || defaultDir == "off" {
    79  			return
    80  		}
    81  		if defaultDir != "" {
    82  			defaultDir = "off"
    83  			defaultDirErr = fmt.Errorf("GOCACHE is not an absolute path")
    84  			return
    85  		}
    86  
    87  		// Compute default location.
    88  		dir, err := os.UserCacheDir()
    89  		if err != nil {
    90  			defaultDir = "off"
    91  			defaultDirErr = fmt.Errorf("GOCACHE is not defined and %v", err)
    92  			return
    93  		}
    94  		defaultDir = filepath.Join(dir, "go-build")
    95  	})
    96  
    97  	return defaultDir
    98  }
    99
View as plain text