Add a way to get how long it takes to cleanup using gc, and a way to disable it.issue264

Fixes #262.

5 files changed, 128 insertions, 15 deletions

diff --git a/src/greenlet/__init__.py b/src/greenlet/__init__.py
index 9f2bcb2..2f671f2 100644
--- a/src/greenlet/__init__.py
+++ b/src/greenlet/__init__.py
@@ -61,3 +61,8 @@ except ImportError:
 from ._greenlet import GREENLET_USE_CONTEXT_VARS # pylint:disable=unused-import
 from ._greenlet import GREENLET_USE_GC # pylint:disable=unused-import
 from ._greenlet import GREENLET_USE_TRACING # pylint:disable=unused-import
+
+# Controlling the use of the gc module.
+from ._greenlet import CLOCKS_PER_SEC # pylint:disable=unused-import
+from ._greenlet import enable_optional_cleanup # pylint:disable=unused-import
+from ._greenlet import get_clocks_used_doing_optional_cleanup # pylint:disable=unused-import
diff --git a/src/greenlet/greenlet.cpp b/src/greenlet/greenlet.cpp
index ab7321c..d915e13 100644
--- a/src/greenlet/greenlet.cpp
+++ b/src/greenlet/greenlet.cpp
@@ -2739,6 +2739,68 @@ mod_get_total_main_greenlets(PyObject* UNUSED(module))
     return PyLong_FromSize_t(total_main_greenlets);
 }
 
+PyDoc_STRVAR(mod_get_clocks_used_doing_optional_cleanup_doc,
+             "get_clocks_used_doing_optional_cleanup() -> Integer\n"
+             "\n"
+             "Get the number of clock ticks the program has used doing optional "
+             "greenlet cleanup.\n"
+             "Beginning in greenlet 2.0, greenlet tries to find and dispose of greenlets\n"
+             "that leaked after a thread exited. This requires invoking Python's garbage collector,\n"
+             "which may have a performance cost proportional to the number of live objects.\n"
+             "This function returns the amount of processor time\n"
+             "greenlet has used to do this. In programs that run with very large amounts of live\n"
+             "objects, this metric can be used to decide whether the cost of doing this cleanup\n"
+             "is worth the memory leak being corrected. If not, you can disable the cleanup\n"
+             "using ``enable_optional_cleanup(False)``.\n"
+             "The units are arbitrary and can only be compared to themselves (similarly to ``time.clock()``);\n"
+             "for example, to see how it scales with your heap. You can attempt to convert them into seconds\n"
+             "by dividing by the value of CLOCKS_PER_SEC."
+             "If cleanup has been disabled, returns None."
+             "\n"
+             "This is an implementation specific, provisional API. It may be changed or removed\n"
+             "in the future.\n"
+             ".. versionadded:: 2.0"
+             );
+static PyObject*
+mod_get_clocks_used_doing_optional_cleanup(PyObject* UNUSED(module))
+{
+    std::clock_t& clocks = ThreadState::clocks_used_doing_gc();
+
+    if (clocks == std::clock_t(-1)) {
+        Py_RETURN_NONE;
+    }
+    // This might not actually work on some implementations; clock_t
+    // is an opaque type.
+    return PyLong_FromSsize_t(clocks);
+}
+
+PyDoc_STRVAR(mod_enable_optional_cleanup_doc,
+             "mod_enable_optional_cleanup(bool) -> None\n"
+             "\n"
+             "Enable or disable optional cleanup operations.\n"
+             "See ``get_clocks_used_doing_optional_cleanup()`` for details.\n"
+             );
+static PyObject*
+mod_enable_optional_cleanup(PyObject* UNUSED(module), PyObject* flag)
+{
+    int is_true = PyObject_IsTrue(flag);
+    if (is_true == -1) {
+        return nullptr;
+    }
+
+    std::clock_t& clocks = ThreadState::clocks_used_doing_gc();
+    if (is_true) {
+        // If we already have a value, we don't want to lose it.
+        if (clocks == std::clock_t(-1)) {
+            clocks = 0;
+        }
+    }
+    else {
+        clocks = std::clock_t(-1);
+    }
+    Py_RETURN_NONE;
+}
+
 static PyMethodDef GreenMethods[] = {
     {"getcurrent",
      (PyCFunction)mod_getcurrent,
@@ -2749,6 +2811,8 @@ static PyMethodDef GreenMethods[] = {
     {"set_thread_local", (PyCFunction)mod_set_thread_local, METH_VARARGS, mod_set_thread_local_doc},
     {"get_pending_cleanup_count", (PyCFunction)mod_get_pending_cleanup_count, METH_NOARGS, mod_get_pending_cleanup_count_doc},
     {"get_total_main_greenlets", (PyCFunction)mod_get_total_main_greenlets, METH_NOARGS, mod_get_total_main_greenlets_doc},
+    {"get_clocks_used_doing_optional_cleanup", (PyCFunction)mod_get_clocks_used_doing_optional_cleanup, METH_NOARGS, mod_get_clocks_used_doing_optional_cleanup_doc},
+    {"enable_optional_cleanup", (PyCFunction)mod_enable_optional_cleanup, METH_O, mod_enable_optional_cleanup_doc},
     {NULL, NULL} /* Sentinel */
 };
 
@@ -2800,6 +2864,9 @@ greenlet_internal_mod_init() G_NOEXCEPT
         m.PyAddObject("GREENLET_USE_CONTEXT_VARS", (long)GREENLET_PY37);
         m.PyAddObject("GREENLET_USE_STANDARD_THREADING", (long)G_USE_STANDARD_THREADING);
 
+        OwnedObject clocks_per_sec = OwnedObject::consuming(PyLong_FromSsize_t(CLOCKS_PER_SEC));
+        m.PyAddObject("CLOCKS_PER_SEC", clocks_per_sec);
+
         /* also publish module-level data as attributes of the greentype. */
         // XXX: This is weird, and enables a strange pattern of
         // confusing the class greenlet with the module greenlet; with
diff --git a/src/greenlet/greenlet_internal.hpp b/src/greenlet/greenlet_internal.hpp
index fc25673..2892b75 100644
--- a/src/greenlet/greenlet_internal.hpp
+++ b/src/greenlet/greenlet_internal.hpp
@@ -28,8 +28,6 @@ namespace greenlet {
 
     class ThreadState;
 
-    typedef std::vector<PyGreenlet*, PythonAllocator<PyGreenlet*> > g_deleteme_t;
-
 };
 
 
diff --git a/src/greenlet/greenlet_thread_state.hpp b/src/greenlet/greenlet_thread_state.hpp
index fe1e160..c024cf3 100644
--- a/src/greenlet/greenlet_thread_state.hpp
+++ b/src/greenlet/greenlet_thread_state.hpp
@@ -1,6 +1,7 @@
 #ifndef GREENLET_THREAD_STATE_HPP
 #define GREENLET_THREAD_STATE_HPP
 
+#include <ctime>
 #include <stdexcept>
 
 #include "greenlet_internal.hpp"
@@ -103,17 +104,21 @@ private:
     /* Strong reference to the trace function, if any. */
     OwnedObject tracefunc;
 
-    /* A vector of PyGreenlet pointers representing things that need
+    typedef std::vector<PyGreenlet*, PythonAllocator<PyGreenlet*> > deleteme_t;
+    /* A vector of raw PyGreenlet pointers representing things that need
        deleted when this thread is running. The vector owns the
        references, but you need to manually INCREF/DECREF as you use
-       them. */
-    greenlet::g_deleteme_t deleteme;
+       them. We don't use a vector<refs::OwnedGreenlet> because we
+       make copy of this vector, and that would become O(n) as all the
+       refcounts are incremented in the copy.
+    */
+    deleteme_t deleteme;
 
 #ifdef GREENLET_NEEDS_EXCEPTION_STATE_SAVED
     void* exception_state;
 #endif
 
-
+    static std::clock_t _clocks_used_doing_gc;
     static ImmortalString get_referrers_name;
     static PythonAllocator<ThreadState> allocator;
 
@@ -134,6 +139,7 @@ public:
     static void init()
     {
         ThreadState::get_referrers_name = "get_referrers";
+        ThreadState::_clocks_used_doing_gc = 0;
     }
 
     ThreadState()
@@ -256,9 +262,9 @@ private:
             // It's possible we could add items to this list while
             // running Python code if there's a thread switch, so we
             // need to defensively copy it before that can happen.
-            g_deleteme_t copy = this->deleteme;
+            deleteme_t copy = this->deleteme;
             this->deleteme.clear(); // in case things come back on the list
-            for(greenlet::g_deleteme_t::iterator it = copy.begin(), end = copy.end();
+            for(deleteme_t::iterator it = copy.begin(), end = copy.end();
                 it != end;
                 ++it ) {
                 PyGreenlet* to_del = *it;
@@ -320,6 +326,14 @@ public:
         this->deleteme.push_back(to_del);
     }
 
+    /**
+     * Set to std::clock_t(-1) to disable.
+     */
+    inline static std::clock_t& clocks_used_doing_gc()
+    {
+        return ThreadState::_clocks_used_doing_gc;
+    }
+
     ~ThreadState()
     {
         if (!PyInterpreterState_Head()) {
@@ -348,11 +362,6 @@ public:
         // on the stack, somewhere uncollectable. Try to detect that.
         if (this->current_greenlet == this->main_greenlet && this->current_greenlet) {
             assert(this->current_greenlet->is_currently_running_in_some_thread());
-
-            // // Break a cycle we know about, the self reference
-            // // the main greenlet keeps.
-            // this->main_greenlet->main_greenlet.CLEAR();
-
             // Drop one reference we hold.
             this->current_greenlet.CLEAR();
             assert(!this->current_greenlet);
@@ -361,12 +370,14 @@ public:
             PyGreenlet* old_main_greenlet = this->main_greenlet.borrow();
             Py_ssize_t cnt = this->main_greenlet.REFCNT();
             this->main_greenlet.CLEAR();
-            if (cnt == 2 && Py_REFCNT(old_main_greenlet) == 1) {
+            if (ThreadState::_clocks_used_doing_gc != std::clock_t(-1)
+                && cnt == 2 && Py_REFCNT(old_main_greenlet) == 1) {
                 // Highly likely that the reference is somewhere on
                 // the stack, not reachable by GC. Verify.
                 // XXX: This is O(n) in the total number of objects.
                 // TODO: Add a way to disable this at runtime, and
                 // another way to report on it.
+                std::clock_t begin = std::clock();
                 NewReference gc(PyImport_ImportModule("gc"));
                 if (gc) {
                     OwnedObject get_referrers = gc.PyRequireAttr(ThreadState::get_referrers_name);
@@ -412,6 +423,8 @@ public:
                             }
                         }
                     }
+                    std::clock_t end = std::clock();
+                    ThreadState::_clocks_used_doing_gc += (end - begin);
                 }
             }
         }
@@ -453,6 +466,7 @@ public:
 
 ImmortalString ThreadState::get_referrers_name(nullptr);
 PythonAllocator<ThreadState> ThreadState::allocator;
+std::clock_t ThreadState::_clocks_used_doing_gc(0);
 
 template<typename Destructor>
 class ThreadStateCreator
diff --git a/src/greenlet/tests/test_leaks.py b/src/greenlet/tests/test_leaks.py
index 946425b..7ff4e59 100644
--- a/src/greenlet/tests/test_leaks.py
+++ b/src/greenlet/tests/test_leaks.py
@@ -116,6 +116,15 @@ class TestLeaks(TestCase):
         for g in gg:
             self.assertIsNone(g())
 
+    def assertClocksUsed(self):
+        used = greenlet._greenlet.get_clocks_used_doing_optional_cleanup()
+        self.assertGreaterEqual(used, 0)
+        # we don't lose the value
+        greenlet._greenlet.enable_optional_cleanup(True)
+        used2 = greenlet._greenlet.get_clocks_used_doing_optional_cleanup()
+        self.assertEqual(used, used2)
+        self.assertGreater(greenlet._greenlet.CLOCKS_PER_SEC, 1)
+
     def _check_issue251(self,
                         manually_collect_background=True,
                         explicit_reference_to_switch=False):
@@ -216,7 +225,8 @@ class TestLeaks(TestCase):
         # the ``greenlet.switch`` method still on the stack that we
         # can't reach to clean up. The C code goes through terrific
         # lengths to clean that up.
-        if not explicit_reference_to_switch:
+        if not explicit_reference_to_switch and greenlet._greenlet.get_clocks_used_doing_optional_cleanup() is not None:
+            # If cleanup was disabled, though, we may not find it.
             self.assertEqual(greenlets_after, greenlets_before)
             if manually_collect_background:
                 # TODO: Figure out how to make this work!
@@ -237,9 +247,19 @@ class TestLeaks(TestCase):
             # done by leakcheck will find it.
             pass
 
+        if greenlet._greenlet.get_clocks_used_doing_optional_cleanup() is not None:
+            self.assertClocksUsed()
+
     def test_issue251_killing_cross_thread_leaks_list(self):
         self._check_issue251()
 
+    def test_issue251_with_cleanup_disabled(self):
+        greenlet._greenlet.enable_optional_cleanup(False)
+        try:
+            self._check_issue251()
+        finally:
+            greenlet._greenlet.enable_optional_cleanup(True)
+
     @fails_leakcheck
     def test_issue251_issue252_need_to_collect_in_background(self):
         # Between greenlet 1.1.2 and the next version, this was still
@@ -262,6 +282,15 @@ class TestLeaks(TestCase):
         self._check_issue251(manually_collect_background=False)
 
     @fails_leakcheck
+    def test_issue251_issue252_need_to_collect_in_background_cleanup_disabled(self):
+        self.expect_greenlet_leak = True
+        greenlet._greenlet.enable_optional_cleanup(False)
+        try:
+            self._check_issue251(manually_collect_background=False)
+        finally:
+            greenlet._greenlet.enable_optional_cleanup(True)
+
+    @fails_leakcheck
     def test_issue251_issue252_explicit_reference_not_collectable(self):
         self._check_issue251(
             manually_collect_background=False,