Moved `resource.getrlimit()`

Removed `resource.getrlimit()` functionality from app.py
Added `resource.getrlimit()` functionality to platform.py as function
Called new function from __init__.py of linux.py and unix.py

buildstream/_frontend/app.py

@@ -116,14 +116,6 @@ class App():
         else:
             self.colors = False
 
-        # Increase the soft limit for open file descriptors to the maximum.
-        # SafeHardlinks FUSE needs to hold file descriptors for all processes in the sandbox.
-        # Avoid hitting the limit too quickly.
-        limits = resource.getrlimit(resource.RLIMIT_NOFILE)
-        if limits[0] != limits[1]:
-            # Set soft limit to hard limit
-            resource.setrlimit(resource.RLIMIT_NOFILE, (limits[1], limits[1]))
-
     # create()
     #
     # Should be used instead of the regular constructor.

buildstream/_platform/linux.py

@@ -52,7 +52,6 @@ class Linux(Platform):
     #              Private Methods                 #
     ################################################
     def _check_user_ns_available(self, context):
-
         # Here, lets check if bwrap is able to create user namespaces,
         # issue a warning if it's not available, and save the state
         # locally so that we can inform the sandbox to not try it

buildstream/_platform/platform.py

@@ -37,6 +37,7 @@ class Platform():
     #
     def __init__(self, context):
         self.context = context
+        self.set_resources()
 
     @classmethod
     def create_instance(cls, *args, **kwargs):
@@ -92,3 +93,15 @@ class Platform():
     def create_sandbox(self, *args, **kwargs):
         raise ImplError("Platform {platform} does not implement create_sandbox()"
                         .format(platform=type(self).__name__))
+
+    def set_resources(self, soft_limit=None, hard_limit=None):
+        # Need to set resources for _frontend/app.py as this is dependent on the platform
+        # SafeHardlinks FUSE needs to hold file descriptors for all processes in the sandbox.
+        # Avoid hitting the limit too quickly.
+        limits = resource.getrlimit(resource.RLIMIT_NOFILE)
+        if limits[0] != limits[1]:
+            if soft_limit is None:
+                soft_limit = limits[1]
+            if hard_limit is None:
+                hard_limit = limits[1]
+            resource.setrlimit(resource.RLIMIT_NOFILE, (soft_limit, hard_limit))

buildstream/_platform/unix.py

@@ -18,6 +18,7 @@
 #        Tristan Maat <tristan.maat@codethink.co.uk>
 
 import os
+import resource
 
 from .._artifactcache.cascache import CASCache
 from .._exceptions import PlatformError