functions to get cache information (#281)

* get cache information - close #280

* update changelog

Author: hroskes

CHANGELOG.rst

@@ -7,6 +7,8 @@
 * update docs for 8.12 [jcupitt]
 * add pagesplit(), pagejoin(), get_page_height(), get_n_pages() [jcupitt]
 * add atan2() [jcupitt]
+* add `cache_get_max()`, `cache_get_max_mem()`, `cache_get_max_files()`, 
+  `cache_get_size()` [hroskes]
 * don't generate docs for deprecated arguments [jcupitt]
 * buffer save tries with the target API first [jcupitt]
 

pyvips/vdecls.py

@@ -383,6 +383,10 @@ def cdefs(features):
         void vips_cache_set_max_files (int max_files);
         void vips_cache_set_trace (int trace);
 
+        int vips_cache_get_max();
+        int vips_cache_get_size();
+        size_t vips_cache_get_max_mem();
+        int vips_cache_get_max_files();
     '''
 
     if _at_least(features, 8, 5):

pyvips/voperation.py

@@ -564,8 +564,30 @@ def cache_set_trace(trace):
     vips_lib.vips_cache_set_trace(trace)
 
 
+def cache_get_max():
+    """Get the maximum number of operations libvips will cache."""
+    return vips_lib.vips_cache_get_max()
+
+
+def cache_get_size():
+    """Get the current size of the operations cache."""
+    return vips_lib.vips_cache_get_size()
+
+
+def cache_get_max_mem():
+    """Get the operation cache limit by memory use."""
+    return vips_lib.vips_cache_get_max_mem()
+
+
+def cache_get_max_files():
+    """Get the operation cache limit by number of open files."""
+    return vips_lib.vips_cache_get_max_files()
+
+
 __all__ = [
     'Introspect', 'Operation',
     'cache_set_max', 'cache_set_max_mem', 'cache_set_max_files',
-    'cache_set_trace'
+    'cache_set_trace',
+    'cache_get_max', 'cache_get_max_mem', 'cache_get_max_files',
+    'cache_get_size',
 ]