add some locking to deal with two bureaus wanting to use the small printer at the same time

screenless/bureau/bureau.py

@@ -1,5 +1,6 @@
 # bureau
 import configparser
+import fcntl
 import functools
 import glob
 import inspect
@@ -87,6 +88,8 @@ class LogPrinter(logging.Handler):
         logging.Handler.__init__(self)
 
     def emit(self, record):
+        sm_print_lockfile = open("small_printer_lock", "w")
+        fcntl.lockf(sm_print_lockfile, fcntl.LOCK_EX)
         if (self.printer["inep"] is None) and (self.printer["outep"] is None):
             prn = printer.Usb(self.printer["vendorid"], self.printer["productid"])
         else:
@@ -106,6 +109,8 @@ class LogPrinter(logging.Handler):
         prn.text(out_text)
         prn.cut()
         prn.close()
+        fcntl.lockf(sm_print_lockfile, fcntl.LOCK_EX)
+        sm_print_lockfile.close()
 
 
 class KeyValStore(object):
@@ -418,6 +423,8 @@ class Bureau(object):
         """
         returns an instance of the small escpos printer
         """
+        self._sm_print_lockfile = open("small_printer_lock", "w")
+        fcntl.lockf(self._sm_print_lockfile, fcntl.LOCK_EX)
         if (self.smprint["inep"] is None) and (self.smprint["outep"] is None):
             prn = printer.Usb(self.smprint["vendorid"],
                               self.smprint["productid"])
@@ -429,6 +436,14 @@ class Bureau(object):
         prn.profile = self.smprint["profile"]
         return prn
 
+    def _free_small_printer(self, printer):
+        """
+        cleans up and unlocks the small printer
+        """
+        printer.close()
+        fcntl.lockf(self._sm_print_lockfile, fcntl.LOCK_UN)
+        self._sm_print_lockfile.close()
+
 
     def print_full(self, template, **kwargs):
         """print a full page (A4) document """
@@ -485,7 +500,7 @@ class Bureau(object):
             prn.ln(2)
         if cut:
             prn.cut()
-        prn.close()
+        self._free_small_printer(prn)
 
     def print_small_image(self, img, linefeed=True):
         """
@@ -507,6 +522,7 @@ class Bureau(object):
         prn.image(im, impl="bitImageColumn")  
         if linefeed:
             prn.ln()
+        self._free_small_printer(prn)
 
     @add_command("test")
     def test(self, data=None):