Fix host memory detection on macOS

pyproject.toml

@@ -32,7 +32,7 @@ classifiers = [
   "Typing :: Typed",
 ]
 dynamic = ["version"]
-dependencies = ["array-api-compat>=1.12", "numpy>=2.0,<3", "opt_einsum>=3.4.0"]
+dependencies = ["array-api-compat>=1.12", "numpy>=2.0,<3", "opt_einsum>=3.4.0", "psutil"]
 
 
 [project.optional-dependencies]

src/src_method/utils/_backend.py

@@ -9,16 +9,18 @@
 synchronous no-ops, so the same algorithm code runs on both backends.
 """
 
 from __future__ import annotations
 
 import os
 from contextlib import contextmanager
 from pathlib import Path
 from typing import TYPE_CHECKING, Any, TypeAlias
 
 import numpy as np
 from array_api_compat import numpy as np_compat
 
+import psutil
+
 if TYPE_CHECKING:
     from collections.abc import Iterator, Sequence
     from types import ModuleType
@@ -378,10 +380,15 @@
         for line in path.read_text().splitlines():
             if line.startswith("MemAvailable:"):
                 return int(line.split()[1]) * 1024
-    return os.sysconf("SC_AVPHYS_PAGES") * os.sysconf("SC_PAGE_SIZE")
+
+    try:
+        return os.sysconf("SC_AVPHYS_PAGES") * os.sysconf("SC_PAGE_SIZE")
+    except (ValueError, OSError):
+        return psutil.virtual_memory().available
+
 
 
 def sketch_dtype(dtype: DTypeLike | None, *inputs: Sequence[Site]) -> np.dtype:
     """Resolve the sketch dtype.
 
     Args: