Now writes images to temporary files and atomically moves in place*

* on systems with an atomic os.rename

overviewer_core/assetmanager.py

@@ -144,11 +144,10 @@ directory.
 
 
         jsondump = json.dumps(dump, indent=4)
-        with codecs.open(os.path.join(self.outputdir, 'overviewerConfig.js'), 'w', encoding='UTF-8') as f:
+        with util.FileReplacer(os.path.join(self.outputdir, "overviewerConfig.js")) as tmpfile:
-            f.write("var overviewerConfig = " + jsondump + ";\n")
+            with codecs.open(tmpfile, 'w', encoding='UTF-8') as f:
+                f.write("var overviewerConfig = " + jsondump + ";\n")
 
-          
-        
         # copy web assets into destdir:
         global_assets = os.path.join(util.get_program_path(), "overviewer_core", "data", "web_assets")
         if not os.path.isdir(global_assets):
@@ -159,23 +158,16 @@ directory.
         js_src = os.path.join(util.get_program_path(), "overviewer_core", "data", "js_src")
         if not os.path.isdir(js_src):
             js_src = os.path.join(util.get_program_path(), "js_src")
-        with open(os.path.join(self.outputdir, "overviewer.js"), "w") as fout:
+        with util.FileReplacer(os.path.join(self.outputdir, "overviewer.js")) as tmpfile:
-            # first copy in js_src/overviewer.js
+            with open(tmpfile, "w") as fout:
-            with open(os.path.join(js_src, "overviewer.js")) as f:
+                # first copy in js_src/overviewer.js
-                fout.write(f.read())
+                with open(os.path.join(js_src, "overviewer.js"), 'r') as f:
-            # now copy in the rest
+                    fout.write(f.read())
-            for js in os.listdir(js_src):
+                # now copy in the rest
-                if not js.endswith("overviewer.js") and js.endswith(".js"):
+                for js in os.listdir(js_src):
-                    with open(os.path.join(js_src,js)) as f:
+                    if not js.endswith("overviewer.js") and js.endswith(".js"):
-                        fout.write(f.read())
+                        with open(os.path.join(js_src,js)) as f:
-        
+                            fout.write(f.read())
-        # do the same with the local copy, if we have it
-        # TODO 
-        # if self.web_assets_path:
-        #    util.mirror_dir(self.web_assets_path, self.outputdir)
-
-
-
         # helper function to get a label for the given rendermode
         def get_render_mode_label(rendermode):
             info = get_render_mode_info(rendermode)
@@ -193,7 +185,6 @@ directory.
         versionstr = "%s (%s)" % (overviewer_version.VERSION, overviewer_version.HASH[:7])
         index = index.replace("{version}", versionstr)
 
-        with codecs.open(os.path.join(self.outputdir, "index.html"), 'w', encoding='UTF-8') as output:
+        with util.FileReplacer(indexpath) as indexpath:
-            output.write(index)
+            with codecs.open(indexpath, 'w', encoding='UTF-8') as output:
-
+                output.write(index)
-

overviewer_core/tileset.py

@@ -28,6 +28,7 @@ from collections import namedtuple
 from PIL import Image
 
 from .util import iterate_base4, convert_coords, unconvert_coords, get_tiles_by_chunk
+from .util import FileReplacer
 from .optimizeimages import optimize_image
 import c_overviewer
 
@@ -784,15 +785,16 @@ class TileSet(object):
                     logging.error("While attempting to delete corrupt image %s, an error was encountered. You will need to delete it yourself. Error was '%s'", path[1], e)
 
         # Save it
-        if imgformat == 'jpg':
+        with FileReplacer(imgpath) as tmppath:
-            img.save(imgpath, quality=self.options['imgquality'], subsampling=0)
+            if imgformat == 'jpg':
-        else: # png
+                img.save(tmppath, "jpeg", quality=self.options['imgquality'], subsampling=0)
-            img.save(imgpath)
+            else: # png
-            
+                img.save(tmppath, "png")
-        if self.options['optimizeimg']:
+                
-            optimize_image(imgpath, imgformat, self.options['optimizeimg'])
+            if self.options['optimizeimg']:
+                optimize_image(tmppath, imgformat, self.options['optimizeimg'])
 
-        os.utime(imgpath, (max_mtime, max_mtime))
+            os.utime(tmppath, (max_mtime, max_mtime))
 
     def _render_rendertile(self, tile):
         """Renders the given render-tile.
@@ -877,15 +879,16 @@ class TileSet(object):
                 draw.text((96,96), "c,r: %s,%s" % (col, row), fill='red')
         
         # Save them
-        if self.imgextension == 'jpg':
+        with FileReplacer(imgpath) as tmppath:
-            tileimg.save(imgpath, quality=self.options['imgquality'], subsampling=0)
+            if self.imgextension == 'jpg':
-        else: # png
+                tileimg.save(tmppath, "jpeg", quality=self.options['imgquality'], subsampling=0)
-            tileimg.save(imgpath)
+            else: # png
+                tileimg.save(tmppath, "png")
 
-        if self.options['optimizeimg']:
+            if self.options['optimizeimg']:
-            optimize_image(imgpath, self.imgextension, self.options['optimizeimg'])
+                optimize_image(tmppath, self.imgextension, self.options['optimizeimg'])
 
-        os.utime(imgpath, (max_chunk_mtime, max_chunk_mtime))
+            os.utime(tmppath, (max_chunk_mtime, max_chunk_mtime))
 
     def _get_chunks_for_tile(self, tile):
         """Get chunks that are relevant to the given render-tile

overviewer_core/util.py

@@ -178,6 +178,74 @@ def get_tiles_by_chunk(chunkcol, chunkrow):
 
     return product(colrange, rowrange)
 
+# Define a context manager to handle atomic renaming or "just forget it write
+# straight to the file" depending on whether os.rename provides atomic
+# overwrites.
+# Detect whether os.rename will overwrite files
+import tempfile
+with tempfile.NamedTemporaryFile() as f1:
+    with tempfile.NamedTemporaryFile() as f2:
+        try:
+            os.rename(f1.name,f2.name)
+        except OSError:
+            renameworks = False
+        else:
+            renameworks = True
+            # re-make this file so it can be deleted without error
+            open(f1.name, 'w').close()
+del tempfile,f1,f2
+doc = """This class acts as a context manager for files that are to be written
+out overwriting an existing file.
+
+The parameter is the destination filename. The value returned into the context
+is the filename that should be used. On systems that support an atomic
+os.rename(), the filename will actually be a temporary file, and it will be
+atomically replaced over the destination file on exit.
+
+On systems that don't support an atomic rename, the filename returned is the
+filename given.
+
+If an error is encountered, the file is attempted to be removed, and the error
+is propagated.
+
+Example:
+
+with FileReplacer("config") as configname:
+    with open(configout, 'w') as configout:
+        configout.write(newconfig)
+"""
+if renameworks:
+    class FileReplacer(object):
+        __doc__ = doc
+        def __init__(self, destname):
+            self.destname = destname
+            self.tmpname = destname + ".tmp"
+        def __enter__(self):
+            # rename works here. Return a temporary filename
+            return self.tmpname
+        def __exit__(self, exc_type, exc_val, exc_tb):
+            if exc_type:
+                # error
+                try:
+                    os.remove(self.tmpname)
+                except Exception, e:
+                    logging.warning("An error was raised, so I was doing "
+                            "some cleanup first, but I couldn't remove "
+                            "'%s'!", self.tmpname)
+            else:
+                # atomic rename into place
+                os.rename(self.tmpname, self.destname)
+else:
+    class FileReplacer(object):
+        __doc__ = doc
+        def __init__(self, destname):
+            self.destname = destname
+        def __enter__(self):
+            return self.destname
+        def __exit__(self, exc_type, exc_val, exc_tb):
+            return
+del renameworks
+
 # Logging related classes are below
 
 # Some cool code for colored logging: