default.go

Documentation: cmd/go/internal/cache

     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  	"internal/goexperiment"
    16  )
    17  
    18  // Default returns the default cache to use.
    19  // It never returns nil.
    20  func Default() Cache {
    21  	defaultOnce.Do(initDefaultCache)
    22  	return defaultCache
    23  }
    24  
    25  var (
    26  	defaultOnce  sync.Once
    27  	defaultCache Cache
    28  )
    29  
    30  // cacheREADME is a message stored in a README in the cache directory.
    31  // Because the cache lives outside the normal Go trees, we leave the
    32  // README as a courtesy to explain where it came from.
    33  const cacheREADME = `This directory holds cached build artifacts from the Go build system.
    34  Run "go clean -cache" if the directory is getting too large.
    35  Run "go clean -fuzzcache" to delete the fuzz cache.
    36  See golang.org to learn more about Go.
    37  `
    38  
    39  // initDefaultCache does the work of finding the default cache
    40  // the first time Default is called.
    41  func initDefaultCache() {
    42  	dir, _ := DefaultDir()
    43  	if dir == "off" {
    44  		if defaultDirErr != nil {
    45  			base.Fatalf("build cache is required, but could not be located: %v", defaultDirErr)
    46  		}
    47  		base.Fatalf("build cache is disabled by GOCACHE=off, but required as of Go 1.12")
    48  	}
    49  	if err := os.MkdirAll(dir, 0777); err != nil {
    50  		base.Fatalf("failed to initialize build cache at %s: %s\n", dir, err)
    51  	}
    52  	if _, err := os.Stat(filepath.Join(dir, "README")); err != nil {
    53  		// Best effort.
    54  		os.WriteFile(filepath.Join(dir, "README"), []byte(cacheREADME), 0666)
    55  	}
    56  
    57  	diskCache, err := Open(dir)
    58  	if err != nil {
    59  		base.Fatalf("failed to initialize build cache at %s: %s\n", dir, err)
    60  	}
    61  
    62  	if v := cfg.Getenv("GOCACHEPROG"); v != "" && goexperiment.CacheProg {
    63  		defaultCache = startCacheProg(v, diskCache)
    64  	} else {
    65  		defaultCache = diskCache
    66  	}
    67  }
    68  
    69  var (
    70  	defaultDirOnce    sync.Once
    71  	defaultDir        string
    72  	defaultDirChanged bool // effective value differs from $GOCACHE
    73  	defaultDirErr     error
    74  )
    75  
    76  // DefaultDir returns the effective GOCACHE setting.
    77  // It returns "off" if the cache is disabled,
    78  // and reports whether the effective value differs from GOCACHE.
    79  func DefaultDir() (string, bool) {
    80  	// Save the result of the first call to DefaultDir for later use in
    81  	// initDefaultCache. cmd/go/main.go explicitly sets GOCACHE so that
    82  	// subprocesses will inherit it, but that means initDefaultCache can't
    83  	// otherwise distinguish between an explicit "off" and a UserCacheDir error.
    84  
    85  	defaultDirOnce.Do(func() {
    86  		defaultDir = cfg.Getenv("GOCACHE")
    87  		if defaultDir != "" {
    88  			defaultDirChanged = true
    89  			if filepath.IsAbs(defaultDir) || defaultDir == "off" {
    90  				return
    91  			}
    92  			defaultDir = "off"
    93  			defaultDirErr = fmt.Errorf("GOCACHE is not an absolute path")
    94  			return
    95  		}
    96  
    97  		// Compute default location.
    98  		dir, err := os.UserCacheDir()
    99  		if err != nil {
   100  			defaultDir = "off"
   101  			defaultDirChanged = true
   102  			defaultDirErr = fmt.Errorf("GOCACHE is not defined and %v", err)
   103  			return
   104  		}
   105  		defaultDir = filepath.Join(dir, "go-build")
   106  	})
   107  
   108  	return defaultDir, defaultDirChanged
   109  }
   110
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