1 files changed, 33 insertions, 0 deletions
diff --git a/Modules/hashlib.h b/Modules/hashlib.h
index db39cea..7cb6ee5 100644
--- a/Modules/hashlib.h
+++ b/Modules/hashlib.h
@@ -26,3 +26,36 @@
             return NULL; \
         } \
     } while(0);
+
+/*
+ * Helper code to synchronize access to the hash object when the GIL is
+ * released around a CPU consuming hashlib operation. All code paths that
+ * access a mutable part of obj must be enclosed in a ENTER_HASHLIB /
+ * LEAVE_HASHLIB block or explicitly acquire and release the lock inside
+ * a PY_BEGIN / END_ALLOW_THREADS block if they wish to release the GIL for
+ * an operation.
+ */
+
+#ifdef WITH_THREAD
+#include "pythread.h"
+    #define ENTER_HASHLIB(obj) \
+        if ((obj)->lock) { \
+            if (!PyThread_acquire_lock((obj)->lock, 0)) { \
+                Py_BEGIN_ALLOW_THREADS \
+                PyThread_acquire_lock((obj)->lock, 1); \
+                Py_END_ALLOW_THREADS \
+            } \
+        }
+    #define LEAVE_HASHLIB(obj) \
+        if ((obj)->lock) { \
+            PyThread_release_lock((obj)->lock); \
+        }
+#else
+    #define ENTER_HASHLIB(obj)
+    #define LEAVE_HASHLIB(obj)
+#endif
+
+/* TODO(gps): We should probably make this a module or EVPobject attribute
+ * to allow the user to optimize based on the platform they're using. */
+#define HASHLIB_GIL_MINSIZE 2048
+