cmdpipe manual piping/parallel executing tested and done

zfs_autobackup/CmdPipe.py

@@ -1,8 +1,16 @@
 # This is the low level process executing stuff.
-# It makes piping multiple process easier.
+# It makes piping and parallel process handling more easy.
+
 # You can specify a handler for each line of stderr output for each item in the pipe.
 # Every item also has its own exitcode handler.
-# There is one stdout handler for the last item in the pipe. This is also called for each line.
+
+# Normally you add a stdout_handler to the last item in the pipe.
+# However: You can also add stdout_handler to other items in a pipe. This will turn that item in to a manual pipe: your
+# handler is responsible for sending data into the next item of the pipe. (avaiable in item.next)
+
+# You can also use manual pipe mode to just execute multiple command in parallel and handle their output parallel,
+# without doing any actual pipe stuff. (because you dont HAVE to send data into the next item.)
+
 
 import subprocess
 import os
@@ -33,7 +41,7 @@ class CmdItem:
         self.exit_handler = exit_handler
         self.shell = shell
         self.process = None
-        self.next_item = None #next item in pipe, set by CmdPipe
+        self.next = None #next item in pipe, set by CmdPipe
 
     def __str__(self):
         """return copy-pastable version of command."""
@@ -97,55 +105,38 @@ class CmdPipe:
         return self._should_execute
 
     def execute(self):
-        """run the pipe. returns True all exit handlers returned true"""
+        """run the pipe. returns True all exit handlers returned true. (otherwise it will be False/None depending on exit handlers returncode) """
 
         if not self._should_execute:
             return True
 
-        selectors = []
+        selectors = self.__create()
 
-        # create processes
-        last_stdout = None
-        next_stdin = subprocess.PIPE # means we write input via python instead of an actual system pipe
-        first=True
-        prev_item=None
+        if not selectors:
+            raise (Exception("Cant use cmdpipe without any output handlers."))
+
+        self.__process_outputs(selectors)
+
+        # close filehandles
         for item in self.items:
+            item.process.stderr.close()
+            item.process.stdout.close()
 
-            #creates the actual subprocess via subprocess.popen
-            item.create(next_stdin)
+        # call exit handlers
+        success = True
+        for item in self.items:
+            if item.exit_handler is not None:
+                success=item.exit_handler(item.process.returncode) and success
 
-            #we piped previous process? dont forget to close its stdout
-            if next_stdin != subprocess.PIPE:
-                next_stdin.close()
+        return success
 
-            selectors.append(item.process.stderr)
-
-            # we're the first process in the pipe
-            if first:
-                if self.inp is not None:
-                    #write the input we have
-                    item.process.stdin.write(self.inp.encode('utf-8'))
-                item.process.stdin.close()
-                first=False
-
-            #manual stdout handling or pipe it to the next process?
-            if item.stdout_handler is None:
-                # no manual stdout handling, pipe it to the next process via sytem pipe
-                next_stdin=item.process.stdout
-            else:
-                # manual stdout handling via python
-                selectors.append(item.process.stdout)
-                # next process will get input from python:
-                next_stdin= subprocess.PIPE
-
-            if prev_item is not None:
-                prev_item.next=item
-
-            prev_item=item
+    def __process_outputs(self, selectors):
+        """watch all output selectors and call handlers"""
 
         while True:
             # wait for output on one of the stderrs or last_stdout
             (read_ready, write_ready, ex_ready) = select.select(selectors, [], [])
+
             eof_count = 0
             done_count = 0
 
@@ -165,6 +156,8 @@ class CmdPipe:
                         item.stdout_handler(line)
                     else:
                         eof_count = eof_count + 1
+                        if item.next:
+                            item.next.process.stdin.close()
 
                 if item.process.poll() is not None:
                     done_count = done_count + 1
@@ -173,16 +166,48 @@ class CmdPipe:
             if eof_count == len(selectors) and done_count == len(self.items):
                 break
 
-        # close filehandles
-        for item in self.items:
-            item.process.stderr.close()
-            item.process.stdout.close()
-            # item.process.stdin.close()
 
-        # call exit handlers
-        success = True
-        for item in self.items:
-            if item.exit_handler is not None:
-                success=item.exit_handler(item.process.returncode) and success
 
-        return success
+    def __create(self):
+        """create actual processes, do piping and return selectors."""
+
+        selectors = []
+        next_stdin = subprocess.PIPE  # means we write input via python instead of an actual system pipe
+        first = True
+        prev_item = None
+
+        for item in self.items:
+
+            # creates the actual subprocess via subprocess.popen
+            item.create(next_stdin)
+
+            # we piped previous process? dont forget to close its stdout
+            if next_stdin != subprocess.PIPE:
+                next_stdin.close()
+
+            if item.stderr_handler:
+                selectors.append(item.process.stderr)
+
+            # we're the first process in the pipe
+            if first:
+                if self.inp is not None:
+                    # write the input we have
+                    item.process.stdin.write(self.inp.encode('utf-8'))
+                item.process.stdin.close()
+                first = False
+
+            # manual stdout handling or pipe it to the next process?
+            if item.stdout_handler is None:
+                # no manual stdout handling, pipe it to the next process via sytem pipe
+                next_stdin = item.process.stdout
+            else:
+                # manual stdout handling via python
+                selectors.append(item.process.stdout)
+                # next process will get input from python:
+                next_stdin = subprocess.PIPE
+
+            if prev_item is not None:
+                prev_item.next = item
+
+            prev_item = item
+        return selectors