Do not overwrite unchanged target

diff --git a/dep.go b/dep.go
index 7c4e35aa700a4edf7c52dcb88b19e344321d3b90..0e4f24fb0a1ef8872145d2715271f8eb5cff8adc 100644 (file)
--- a/dep.go
+++ b/dep.go
@@ -86,7 +86,7 @@ func fileHash(fd *os.File) (string, error) {
        return hex.EncodeToString(h.Sum(nil)), nil
 }
 
-func depWrite(fdDep *os.File, cwd, tgt string) error {
+func depWrite(fdDep *os.File, cwd, tgt, hsh string) error {
        tracef(CDebug, "ifchange: %s <- %s", fdDep.Name(), tgt)
        fd, err := os.Open(path.Join(cwd, tgt))
        if err != nil {
@@ -104,9 +104,11 @@ func depWrite(fdDep *os.File, cwd, tgt string) error {
        if err != nil {
                return err
        }
-       hsh, err := fileHash(fd)
-       if err != nil {
-               return err
+       if hsh == "" {
+               hsh, err = fileHash(fd)
+               if err != nil {
+                       return err
+               }
        }
        fields := []recfile.Field{
                {Name: "Type", Value: DepTypeIfchange},
@@ -137,7 +139,7 @@ func depsWrite(fdDep *os.File, tgts []string) error {
                        panic(err)
                }
                if _, errStat := os.Stat(tgt); errStat == nil {
-                       err = depWrite(fdDep, tgtDir, tgtRel)
+                       err = depWrite(fdDep, tgtDir, tgtRel, "")
                } else {
                        tracef(CDebug, "ifchange: %s <- %s (non-existing)", fdDep.Name(), tgtRel)
                        fields := []recfile.Field{

diff --git a/doc/news.texi b/doc/news.texi
index 6cdbe077851e1b2818a97be93faf8cf8b0967404..088cc03a77955564e3ae881be21abebf7e7fcd6e 100644 (file)
--- a/doc/news.texi
+++ b/doc/news.texi
@@ -12,6 +12,10 @@
 @item
     Inode's number is also stored as dependency information, just to
     prevent possible @code{ctime} collision of two files.
+@item
+    Performance optimization: do not use target's temporary output file
+    at all, if its hash equals to already existing target's one. Just
+    touch existing target file instead.
 @end itemize
 
 @anchor{Release 1_22_0}

diff --git a/run.go b/run.go
index ba841522835e50dad65a5523ff5fe6c4d545ad8c..366240557fff22680d401ae11b3d7de2ddb3ed01 100644 (file)
--- a/run.go
+++ b/run.go
@@ -128,24 +128,26 @@ func mkdirs(pth string) error {
        return os.MkdirAll(pth, os.FileMode(0777))
 }
 
-func isModified(cwd, redoDir, tgt string) (bool, *Inode, error) {
+func isModified(cwd, redoDir, tgt string) (bool, *Inode, string, error) {
        fdDep, err := os.Open(path.Join(redoDir, tgt+DepSuffix))
        if err != nil {
                if os.IsNotExist(err) {
-                       return false, nil, nil
+                       return false, nil, "", nil
                }
-               return false, nil, err
+               return false, nil, "", err
        }
        defer fdDep.Close()
        r := recfile.NewReader(fdDep)
+       var modified bool
        var ourInode *Inode
+       var hshPrev string
        for {
                m, err := r.NextMap()
                if err != nil {
                        if errors.Is(err, io.EOF) {
                                break
                        }
-                       return false, nil, err
+                       return false, nil, "", err
                }
                if m["Type"] != DepTypeIfchange || m["Target"] != tgt {
                        continue
@@ -153,25 +155,24 @@ func isModified(cwd, redoDir, tgt string) (bool, *Inode, error) {
                fd, err := os.Open(path.Join(cwd, tgt))
                if err != nil {
                        if os.IsNotExist(err) {
-                               return false, nil, nil
+                               return false, nil, "", nil
                        }
-                       return false, nil, err
+                       return false, nil, "", err
                }
                ourInode, err = inodeFromFile(fd)
                fd.Close()
                if err != nil {
-                       return false, nil, err
+                       return false, nil, "", err
                }
                theirInode, err := inodeFromRec(m)
                if err != nil {
-                       return false, nil, err
-               }
-               if !ourInode.Equals(theirInode) {
-                       return true, ourInode, nil
+                       return false, nil, "", err
                }
+               hshPrev = m["Hash"]
+               modified = !ourInode.Equals(theirInode)
                break
        }
-       return false, ourInode, nil
+       return modified, ourInode, hshPrev, nil
 }
 
 func syncDir(dir string) error {
@@ -269,7 +270,7 @@ func runScript(tgtOrig string, errs chan error, traced bool) error {
        }
 
        // Check if target is not modified externally
-       modified, inodePrev, err := isModified(cwd, redoDir, tgt)
+       modified, inodePrev, hshPrev, err := isModified(cwd, redoDir, tgt)
        if err != nil {
                lockRelease()
                return TgtError{tgtOrig, err}
@@ -335,7 +336,7 @@ func runScript(tgtOrig string, errs chan error, traced bool) error {
                runErr.DoFile = doFileRelPath
        }
 
-       if err = depWrite(fdDep, cwdOrig, doFileRelPath); err != nil {
+       if err = depWrite(fdDep, cwdOrig, doFileRelPath, ""); err != nil {
                cleanup()
                return TgtError{tgtOrig, err}
        }
@@ -703,6 +704,39 @@ func runScript(tgtOrig string, errs chan error, traced bool) error {
                                goto Finish
                        }
                } else {
+                       var hsh string
+                       if hshPrev != "" {
+                               _, err = fd.Seek(0, io.SeekStart)
+                               if err != nil {
+                                       goto Finish
+                               }
+                               hsh, err = fileHash(fd)
+                               if err != nil {
+                                       goto Finish
+                               }
+                               if hsh == hshPrev {
+                                       tracef(CDebug, "%s has same hash, not renaming", tgtOrig)
+                                       err = os.Remove(fd.Name())
+                                       if err != nil {
+                                               goto Finish
+                                       }
+                                       err = os.Chtimes(path.Join(cwdOrig, tgt), finished, finished)
+                                       if err != nil {
+                                               goto Finish
+                                       }
+                                       if !NoSync {
+                                               err = syncDir(cwdOrig)
+                                               if err != nil {
+                                                       goto Finish
+                                               }
+                                       }
+                                       err = depWrite(fdDep, cwdOrig, tgt, hshPrev)
+                                       if err != nil {
+                                               goto Finish
+                                       }
+                                       goto RecCommit
+                               }
+                       }
                        if !NoSync {
                                err = fd.Sync()
                                if err != nil {
@@ -719,12 +753,13 @@ func runScript(tgtOrig string, errs chan error, traced bool) error {
                                        goto Finish
                                }
                        }
-                       err = depWrite(fdDep, cwdOrig, tgt)
+                       err = depWrite(fdDep, cwdOrig, tgt, hsh)
                        if err != nil {
                                goto Finish
                        }
                }
 
+       RecCommit:
                // Commit .rec
                if !NoSync {
                        err = fdDep.Sync()

diff --git a/t/goredo-empty-dep.t b/t/goredo-empty-dep.t
index a278652bef025acf817896679af453beba4d14ae..63f9e30f8a49c9e769d5a192f47548d73fc6ea47 100755 (executable)
--- a/t/goredo-empty-dep.t
+++ b/t/goredo-empty-dep.t
@@ -12,6 +12,7 @@ echo bar
 EOF
 redo-ifchange bar
 stat1=`stat bar`
+sleep 1 # stat does not output fractions of seconds
 redo-ifchange bar
 stat2=`stat bar`
 

diff --git a/t/goredo-rel-ifcreate.t b/t/goredo-rel-ifcreate.t
index e642f53001408b1afc227c688e30f772eaf8b81c..61d534901c9e395abeb04d159a303a9124d442f6 100755 (executable)
--- a/t/goredo-rel-ifcreate.t
+++ b/t/goredo-rel-ifcreate.t
@@ -14,6 +14,7 @@ redo-ifchange c/dep
 EOF
 redo-ifchange a/b/c/file
 stat1=`stat a/b/c/file`
+sleep 1 # stat does not output fractions of seconds
 redo-ifchange a/b/c/file
 stat2=`stat a/b/c/file`