2 files changed, 32 insertions, 13 deletions
diff --git a/src/buildstream/_platform/darwin.py b/src/buildstream/_platform/darwin.py
index 8e08685ec..282a5b445 100644
--- a/src/buildstream/_platform/darwin.py
+++ b/src/buildstream/_platform/darwin.py
@@ -16,6 +16,7 @@
 #  License along with this library. If not, see <http://www.gnu.org/licenses/>.
 
 import os
+import resource
 
 from ..sandbox import SandboxDummy
 
@@ -44,5 +45,20 @@ class Darwin(Platform):
         else:
             return min(cpu_count, cap)
 
-    def set_resource_limits(self, soft_limit=OPEN_MAX, hard_limit=None):
-        super().set_resource_limits(soft_limit)
+    def maximize_open_file_limit(self):
+        # Note that on Mac OSX, you may not be able to simply set the soft
+        # limit to the reported hard limit, as it may not be the only limit in
+        # effect. The output of these commands may be somewhat independent:
+        #
+        #   $ launchctl limit
+        #   $ sysctl -a | grep files
+        #
+        # The OPEN_MAX value from syslimits.h seems to be fairly safe, although
+        # users may tweak their individual systems to have different values.
+        # Without a way to determine what the real limit is, we risk failing to
+        # increase the limit. Perhaps the complication is why psutil does not
+        # support rlimit on Mac.
+        #
+        old_soft_limit, hard_limit = resource.getrlimit(resource.RLIMIT_NOFILE)
+        soft_limit = min(max(self.OPEN_MAX, old_soft_limit), hard_limit)
+        resource.setrlimit(resource.RLIMIT_NOFILE, (soft_limit, hard_limit))
diff --git a/src/buildstream/_platform/platform.py b/src/buildstream/_platform/platform.py
index 0fbe145f9..5f2b7081a 100644
--- a/src/buildstream/_platform/platform.py
+++ b/src/buildstream/_platform/platform.py
@@ -20,7 +20,6 @@
 import os
 import platform
 import sys
-import resource
 
 import psutil
 
@@ -36,7 +35,7 @@ class Platform():
     # sandbox factory as well as platform helpers.
     #
     def __init__(self):
-        self.set_resource_limits()
+        self.maximize_open_file_limit()
 
     @classmethod
     def _create_instance(cls):
@@ -153,14 +152,18 @@ class Platform():
         raise ImplError("Platform {platform} does not implement check_sandbox_config()"
                         .format(platform=type(self).__name__))
 
-    def set_resource_limits(self, soft_limit=None, hard_limit=None):
+    def maximize_open_file_limit(self):
         # 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))
+        # Avoid hitting the limit too quickly, by increasing it as far as we can.
+
+        # Import this late, as it is not available on Windows. Note that we
+        # could use `psutil.Process().rlimit` instead, but this would introduce
+        # a dependency on the `prlimit(2)` call, which seems to only be
+        # available on Linux. For more info:
+        # https://github.com/giampaolo/psutil/blob/cbf2bafbd33ad21ef63400d94cb313c299e78a45/psutil/_psutil_linux.c#L45
+        import resource
+
+        soft_limit, hard_limit = resource.getrlimit(resource.RLIMIT_NOFILE)
+        if soft_limit != hard_limit:
+            resource.setrlimit(resource.RLIMIT_NOFILE, (hard_limit, hard_limit))