Change the way a Printer is used by the worker

src/main.py

@@ -115,8 +115,6 @@ try:
     worker.start()
 except Exception as e:
     app.logger.error("Could not start the worker because %s ", str(e))
-
-    raise e
     sys.exit(-1)
 
 # The rate limit

src/printer.py

@@ -75,6 +75,7 @@ class Printer(ABC):
         self.ready = False
         self.printer_type = printer_type
         self._lock = threading.Lock()
+        self.used = False
 
     @abstractmethod
     def _has_paper(self) -> bool:
@@ -88,6 +89,13 @@ class Printer(ABC):
     def print_task(self, task_type, data) -> None:
         """Takes a PrintTask and executes it"""
 
+    def use_printer(self) -> None:
+        """Marks the printer as being used """
+        self.used = True
+
+    def free_printer(self) -> None:
+        """Marks the printer as being not used, it's available."""
+        self.used = False
 
 class EscPosPrinter(Printer):
     """

src/printers.py

@@ -6,6 +6,7 @@ the methods expected from printers.
 """
 
 from collections.abc import Set
+import time
 import usb.core
 import usb.util
 from printer import Printer, EscPosPrinter, BrotherPrinter
@@ -41,7 +42,17 @@ class Printers:
 
         # Find all connected USB devices
         devices = usb.core.find(find_all=True, custom_match=_FindClass(7))
-        if not devices:
+        waiting_time_for_printer = 10
+        while not list(devices):
+            self.app.logger.warning(str(waiting_time_for_printer) + " Found no printers, waiting for a printer to connect to the system...")
+            time.sleep(1)
+            waiting_time_for_printer = waiting_time_for_printer - 1
+            devices = usb.core.find(find_all=True, custom_match=_FindClass(7))
+            if waiting_time_for_printer == 0:
+                break
+
+
+        if not list(devices):
             self.app.logger.warning(
                 "No USB devices of class 7 ( printers ) found or pyusb could not access the bus."
             )
@@ -60,6 +71,7 @@ class Printers:
                 product = usb.util.get_string(dev, dev.iProduct)
             except Exception:
                 product = "Unknown"
+
             self.app.logger.debug(
                 "Looking at %s %s (%s:%s)",
                 manufacturer,

src/worker.py

@@ -5,6 +5,7 @@ This is the main printing thread. A worker thread consums Tasks from
 
 import threading
 import time
+import traceback
 from printers import Printers
 
 
@@ -13,7 +14,8 @@ class PrintWorker(threading.Thread):
     A thread used to consume Tasks added to a Print Queue.
 
     On initialisation, the worker will try to find Printers,
-    and on each print, choose an available Printer from a list of Printers.
+    and on each print, if the choosen Printer becomes unavailable, it
+    will choose an available Printer from a list of Printers.
 
     If a print fails, it's not retried, but will be added to a list of completed
     tasks.
@@ -30,8 +32,9 @@ class PrintWorker(threading.Thread):
 
         try:
             self.printers = Printers(self.app)
-            self.printers_obj = self.printers.printers
+            self.printers_obj = self.printers.printers # Get the number of printers connected to the system
-            self.printers = iter(self.printers.printers)
+            self.printers_list = iter(self.printers.printers)
+
         except RuntimeError as e:
             self.app.logger.warning("Could not get any Printers")
             raise e
@@ -53,11 +56,31 @@ class PrintWorker(threading.Thread):
             # we know about, and try to find one that is available.
             # When we find a printer, we acquire it
             # When we are finished with a printer, we release it to the world.
-            while not self.printer or not self.printer.ready:
+
+            # If we do not have a printer, we try to find one
+            while not self.printer:
                 time.sleep(1)
                 try:
-                    self.app.logger.debug("Changing printers")
+                    self.app.logger.debug("Trying to find a available printer for the worker.")
-                    self.printer = next(self.printers)
+
+                    # From the list of printer, we get one.
+                    # If no printer in the list is avaible, we try again from the start of the loop, that we reset.
+                    while self.printer.used or not self.printer:
+                        self.printer = next(self.printers_list)
+                        try:
+                            self.printer = next(self.printer)
+                        except StopIteration as e:
+                            self.app.error("We do not have any available printers. Resetting our list of printers and trying again. " + str(e))
+                            self.printers_list = iter(self.printers.printers)
+                            time.sleep(1)
+                            # TODO : Here, in case there is really no printer available, we will stay in a loop forever. Maybe after a number of tries, we should die.
+
+
+                    # Here, we must have found a Printer() that is
+                    # Printer.used = False, which means it's available.
+                    # Therefore, we mark it used, so no other worker uses it.
+                    self.printer.use_printer()
+
                     self.app.logger.debug(
                         "The worker got a %s printer and it's %s",
                         self.printer.printer_type,
@@ -67,6 +90,11 @@ class PrintWorker(threading.Thread):
                     self.app.logger.error("No printer detected" + str(e))
                     self.printer = None
 
+            # If the printer is not ready, we wait for it to become ready.
+            while not self.printer.ready:
+                self.app.debug("Waiting for our printer to become ready...")
+                time.sleep(1)
+
             if self.state != "idle":
                 self.app.logger("We are not idle, waiting...")
                 time.sleep(1)
@@ -80,6 +108,7 @@ class PrintWorker(threading.Thread):
                 except Exception as e:
                     self.app.logger.error("Could not get a new task ! %s ", str(e))
                     self.state = "idle"
+                    self.printer.free_printer()
                     raise RuntimeError(
                         "We could not get a new task because " + str(e)
                     ) from e
@@ -97,6 +126,8 @@ class PrintWorker(threading.Thread):
                         except RuntimeError as e:
                             self.state = "idle"
                             self.app.logger.error("Could not print : %s", str(e))
+                            self.app.logger.error(traceback.format_exc())
+                            self.printer.free_printer()
                             raise e
 
                         task.status = "completed"
@@ -125,6 +156,7 @@ class PrintWorker(threading.Thread):
         """
         self.app.logger.debug("Giving the worker a break")
         self.state = "drinking-a-beer"
+        self.printer.free_printer()
         self.running = False
 
     def start_worker(self):