Fix memory leak in GzipReader.readall

Author: rhpvorderman

benchmark_scripts/memory_leak_test.py

@@ -0,0 +1,18 @@
+import sys
+from isal import igzip
+import resource
+import gc
+
+for _ in range(10):
+    with igzip.open(sys.argv[1], "rb") as reader:
+        a = reader.read()
+        print(len(a))
+        gc.collect()
+        memory_usage = resource.getrusage(resource.RUSAGE_SELF).ru_maxrss
+        memory_usage_mb = memory_usage / 1024
+        print(f"Maximum memory usage: {memory_usage_mb:.2f} MiB")
+        del(a)
+objects_and_size = [(sys.getsizeof(obj), type(obj)) for obj in
+                    gc.get_objects()]
+objects_and_size.sort(key=lambda x: x[0], reverse=True)
+print(objects_and_size[:10])

src/isal/isal_zlibmodule.c

@@ -1995,14 +1995,16 @@ GzipReader_readall(GzipReader *self, PyObject *Py_UNUSED(ignore))
             return NULL;
         }
         if (written_size == 0) {
+            Py_DECREF(chunk);
             break;
         }
         if (_PyBytes_Resize(&chunk, written_size) < 0) {
             Py_DECREF(chunk_list);
             return NULL;
         }
-        if (PyList_Append(chunk_list, chunk) < 0) {
-            Py_DECREF(chunk);
+        int ret = PyList_Append(chunk_list, chunk);
+        Py_DECREF(chunk);
+        if (ret < 0) {
             Py_DECREF(chunk_list);
             return NULL;
         }
@@ -2014,6 +2016,7 @@ GzipReader_readall(GzipReader *self, PyObject *Py_UNUSED(ignore))
     }
     PyObject *ret = _PyBytes_Join(empty_bytes, chunk_list);
     Py_DECREF(empty_bytes);
+    Py_DECREF(chunk_list);
     return ret;
 }