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Commit 084b834d authored by Toby Dickenson's avatar Toby Dickenson
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trunk/src/Persistence/cPickleCache.c
View file @ 084b834d
......@@ -12,10 +12,85 @@
****************************************************************************/
/*
Objects are stored under three different regimes:
Regime 1: Persistent Classes
Persistent Classes are part of ZClasses. They are stored in the
self->data dictionary, and are never garbage collected.
The klass_items() method returns a sequence of (oid,object) tuples
for every Persistent Class, which should make it possible to
implement garbage collection in Python if necessary.
Regime 2: Ghost Objects
There is no benefit to keeping a ghost object which has no
external references, therefore a weak reference scheme is
used to ensure that ghost objects are removed from memory
as soon as possible, when the last external reference is lost.
Ghost objects are stored in the self->data dictionary. Normally
a dictionary keeps a strong reference on its values, however
this reference count is 'stolen'.
This weak reference scheme leaves a dangling reference, in the
dictionary, when the last external reference is lost. To clean up
this dangling reference the persistent object dealloc function
calls self->cache->_oid_unreferenced(self->oid). The cache looks
up the oid in the dictionary, ensures it points to an object whose
reference count is zero, then removes it from the dictionary. Before
removing the object from the dictionary it must temporarily resurrect
the object in much the same way that class instances are resurrected
before their __del__ is called.
Since ghost objects are stored under a different regime to
non-ghost objects, an extra ghostify function in cPersistenceAPI
replaces self->state=GHOST_STATE assignments that were common in
other persistent classes (such as BTrees).
Regime 3: Non-Ghost Objects
Non-ghost objects are stored in two data structures. Firstly, in
the dictionary along with everything else, with a *strong* reference.
Secondly, they are stored in a doubly-linked-list which encodes
the order in which these objects have been most recently used.
The doubly-link-list nodes contain next and previous pointers
linking together the cache and all non-ghost persistent objects.
The node embedded in the cache is the home position. On every
attribute access a non-ghost object will relink itself just
behind the home position in the ring. Objects accessed least
recently will eventually find themselves positioned after
the home position.
Occasionally other nodes are temporarily inserted in the ring
as position markers. The cache contains a ring_lock flag which
must be set and unset before and after doing so. Only if the flag
is unset can the cache assume that all nodes are either his own
home node, or nodes from persistent objects. This assumption is
useful during the garbage collection process.
The number of non-ghost objects is counted in self->non_ghost_count.
The garbage collection process consists of traversing the ring, and
deactivating (that is, turning into a ghost) every object until
self->non_ghost_count is down to the target size, or until it
reaches the home position again.
Note that objects in the sticky or changed states are still kept
in the ring, however they can not be deactivated. The garbage
collection process must skip such objects, rather than deactivating
them.
*/
static char cPickleCache_doc_string[] =
"Defines the PickleCache used by ZODB Connection objects.\n"
"\n"
"$Id: cPickleCache.c,v 1.50 2002/04/03 00:03:32 jeremy Exp $\n";
"$Id: cPickleCache.c,v 1.51 2002/04/03 17:00:44 htrd Exp $\n";
#define ASSIGN(V,E) {PyObject *__e; __e=(E); Py_XDECREF(V); (V)=__e;}
#define UNLESS(E) if(!(E))
......@@ -30,9 +105,10 @@ static char cPickleCache_doc_string[] =
static PyObject *py__p_oid, *py_reload, *py__p_jar, *py__p_changed;
/* define this for extra debugging checks, and lousy performance */
/* Are any of these checks necessary in production code? How do we
decide when to disable it?
/* define this for extra debugging checks, and lousy performance.
Not really necessary in production code... disable this before
release, providing noone has been reporting and RuntimeErrors
that it uses to report problems.
*/
#define MUCH_RING_CHECKING 1
......@@ -44,23 +120,36 @@ static PyObject *py__p_oid, *py_reload, *py__p_jar, *py__p_changed;
#define ENGINE_NOISE(A) ((void)A)
#endif
/* This object is the pickle cache. The layout of this struct is the same
* as the start of ccobject_head in cPersistence.c
* XXX Why do they need to have the same layouts?
*/
/* This object is the pickle cache. The CACHE_HEAD macro guarantees that
layout of this struct is the same as the start of ccobject_head in
cPersistence.c */
typedef struct {
CACHE_HEAD
int klass_count; /* XXX for ZClass support? */
int klass_count; /* count of persistent classes */
PyObject *data; /* oid -> object dict */
PyObject *jar; /* Connection object */
PyObject *setklassstate; /* ??? */
int cache_size; /* number of items in cache */
int ring_lock; /* ??? */
/* XXX Settable from Python, this appears to be a ratio controlling how
* the cache gets gradually smaller. It is probably an error for this
* to be negative.
*/
int cache_size; /* target number of items in cache */
/* Most of the time the ring contains only:
* many nodes corresponding to persistent objects
* one 'home' node from the cache.
In some cases it is handy to temporarily add other types
of node into the ring as placeholders. 'ring_lock' is a boolean
indicating that someone has already done this. Currently this
is only used by the garbage collection code. */
int ring_lock;
/* 'cache_drain_resistance' controls how quickly the cache size will drop
when it is smaller than the configured size. A value of zero means it will
not drop below the configured size (suitable for most caches). Otherwise,
it will remove cache_non_ghost_count/cache_drain_resistance items from
the cache every time (suitable for rarely used caches, such as those
associated with Zope versions. */
int cache_drain_resistance;
} ccobject;
static int present_in_ring(ccobject *self, CPersistentRing *target);
......@@ -127,6 +216,8 @@ object_from_ring(ccobject *self, CPersistentRing *here, const char *context)
static int
scan_gc_items(ccobject *self,int target)
{
/* This function must only be called with the ring lock held */
cPersistentObject *object;
int error;
CPersistentRing *here = self->ring_home.next;
......@@ -174,8 +265,9 @@ scan_gc_items(ccobject *self,int target)
return 0;
/* At this point we know that the ring only contains nodes from
persistent objects, plus our own home node. We can safely
assume this is a persistent object now we know it is not the home */
persistent objects, plus our own home node. We know this because
the ring lock is held. We can safely assume the current ring
node is a persistent object now we know it is not the home */
object = object_from_ring(self, here, "scan_gc_items");
if (!object)
return -1;
......@@ -190,6 +282,8 @@ scan_gc_items(ccobject *self,int target)
* so that we can follow the link after the ghosted object is
* removed from the ring (via ghostify()).
*/
/* FIXME: This needs to be changed back to a placeholder */
CPersistentRing *next = here->next;
ENGINE_NOISE("G");
......@@ -420,6 +514,8 @@ cc_lru_items(ccobject *self, PyObject *args)
return NULL;
if (self->ring_lock) {
/* When the ring lock is held, we have no way of know which ring nodes
belong to persistent objects, and which a placeholders. */
PyErr_SetString(PyExc_ValueError,
".lru_items() is unavailable during garbage collection");
return NULL;
......@@ -498,6 +594,8 @@ cc_oid_unreferenced(ccobject *self, PyObject *args)
#ifdef Py_TRACE_REFS
#error "this code path has not been tested - Toby Dickenson"
/* not tested, but it should still work. I would appreciate
reports of success */
_Py_NewReference(v);
/* it may be a problem that v->ob_type is still NULL? */
#else
......@@ -682,12 +780,14 @@ cc_add_item(ccobject *self, PyObject *key, PyObject *v)
"Cache values must be persistent objects.");
return -1;
}
/* Is this set of tests necessary? */
class = (PyExtensionClass *)(v->ob_type);
if (!((class->class_flags & PERSISTENT_TYPE_FLAG)
&& v->ob_type->tp_basicsize >= sizeof(cPersistentObject))) {
PyErr_SetString(PyExc_ValueError,
"Cache values must be persistent objects.");
/* Must be either persistent classes (ie ZClasses), or instances
of persistent classes (ie Python classeses that derive from
Persistence.Persistent, BTrees, etc) */
return -1;
}
......@@ -698,7 +798,8 @@ cc_add_item(ccobject *self, PyObject *key, PyObject *v)
if (oid == NULL)
return -1;
/* XXX key and oid should both be PyString objects */
/* XXX key and oid should both be PyString objects.
May be helpful to check this. */
if (PyObject_Cmp(key, oid, &result) < 0) {
Py_DECREF(oid);
return -1;
......
trunk/src/ZODB/cPickleCache.c
View file @ 084b834d
......@@ -12,10 +12,85 @@
****************************************************************************/
/*
Objects are stored under three different regimes:
Regime 1: Persistent Classes
Persistent Classes are part of ZClasses. They are stored in the
self->data dictionary, and are never garbage collected.
The klass_items() method returns a sequence of (oid,object) tuples
for every Persistent Class, which should make it possible to
implement garbage collection in Python if necessary.
Regime 2: Ghost Objects
There is no benefit to keeping a ghost object which has no
external references, therefore a weak reference scheme is
used to ensure that ghost objects are removed from memory
as soon as possible, when the last external reference is lost.
Ghost objects are stored in the self->data dictionary. Normally
a dictionary keeps a strong reference on its values, however
this reference count is 'stolen'.
This weak reference scheme leaves a dangling reference, in the
dictionary, when the last external reference is lost. To clean up
this dangling reference the persistent object dealloc function
calls self->cache->_oid_unreferenced(self->oid). The cache looks
up the oid in the dictionary, ensures it points to an object whose
reference count is zero, then removes it from the dictionary. Before
removing the object from the dictionary it must temporarily resurrect
the object in much the same way that class instances are resurrected
before their __del__ is called.
Since ghost objects are stored under a different regime to
non-ghost objects, an extra ghostify function in cPersistenceAPI
replaces self->state=GHOST_STATE assignments that were common in
other persistent classes (such as BTrees).
Regime 3: Non-Ghost Objects
Non-ghost objects are stored in two data structures. Firstly, in
the dictionary along with everything else, with a *strong* reference.
Secondly, they are stored in a doubly-linked-list which encodes
the order in which these objects have been most recently used.
The doubly-link-list nodes contain next and previous pointers
linking together the cache and all non-ghost persistent objects.
The node embedded in the cache is the home position. On every
attribute access a non-ghost object will relink itself just
behind the home position in the ring. Objects accessed least
recently will eventually find themselves positioned after
the home position.
Occasionally other nodes are temporarily inserted in the ring
as position markers. The cache contains a ring_lock flag which
must be set and unset before and after doing so. Only if the flag
is unset can the cache assume that all nodes are either his own
home node, or nodes from persistent objects. This assumption is
useful during the garbage collection process.
The number of non-ghost objects is counted in self->non_ghost_count.
The garbage collection process consists of traversing the ring, and
deactivating (that is, turning into a ghost) every object until
self->non_ghost_count is down to the target size, or until it
reaches the home position again.
Note that objects in the sticky or changed states are still kept
in the ring, however they can not be deactivated. The garbage
collection process must skip such objects, rather than deactivating
them.
*/
static char cPickleCache_doc_string[] =
"Defines the PickleCache used by ZODB Connection objects.\n"
"\n"
"$Id: cPickleCache.c,v 1.50 2002/04/03 00:03:32 jeremy Exp $\n";
"$Id: cPickleCache.c,v 1.51 2002/04/03 17:00:44 htrd Exp $\n";
#define ASSIGN(V,E) {PyObject *__e; __e=(E); Py_XDECREF(V); (V)=__e;}
#define UNLESS(E) if(!(E))
......@@ -30,9 +105,10 @@ static char cPickleCache_doc_string[] =
static PyObject *py__p_oid, *py_reload, *py__p_jar, *py__p_changed;
/* define this for extra debugging checks, and lousy performance */
/* Are any of these checks necessary in production code? How do we
decide when to disable it?
/* define this for extra debugging checks, and lousy performance.
Not really necessary in production code... disable this before
release, providing noone has been reporting and RuntimeErrors
that it uses to report problems.
*/
#define MUCH_RING_CHECKING 1
......@@ -44,23 +120,36 @@ static PyObject *py__p_oid, *py_reload, *py__p_jar, *py__p_changed;
#define ENGINE_NOISE(A) ((void)A)
#endif
/* This object is the pickle cache. The layout of this struct is the same
* as the start of ccobject_head in cPersistence.c
* XXX Why do they need to have the same layouts?
*/
/* This object is the pickle cache. The CACHE_HEAD macro guarantees that
layout of this struct is the same as the start of ccobject_head in
cPersistence.c */
typedef struct {
CACHE_HEAD
int klass_count; /* XXX for ZClass support? */
int klass_count; /* count of persistent classes */
PyObject *data; /* oid -> object dict */
PyObject *jar; /* Connection object */
PyObject *setklassstate; /* ??? */
int cache_size; /* number of items in cache */
int ring_lock; /* ??? */
/* XXX Settable from Python, this appears to be a ratio controlling how
* the cache gets gradually smaller. It is probably an error for this
* to be negative.
*/
int cache_size; /* target number of items in cache */
/* Most of the time the ring contains only:
* many nodes corresponding to persistent objects
* one 'home' node from the cache.
In some cases it is handy to temporarily add other types
of node into the ring as placeholders. 'ring_lock' is a boolean
indicating that someone has already done this. Currently this
is only used by the garbage collection code. */
int ring_lock;
/* 'cache_drain_resistance' controls how quickly the cache size will drop
when it is smaller than the configured size. A value of zero means it will
not drop below the configured size (suitable for most caches). Otherwise,
it will remove cache_non_ghost_count/cache_drain_resistance items from
the cache every time (suitable for rarely used caches, such as those
associated with Zope versions. */
int cache_drain_resistance;
} ccobject;
static int present_in_ring(ccobject *self, CPersistentRing *target);
......@@ -127,6 +216,8 @@ object_from_ring(ccobject *self, CPersistentRing *here, const char *context)
static int
scan_gc_items(ccobject *self,int target)
{
/* This function must only be called with the ring lock held */
cPersistentObject *object;
int error;
CPersistentRing *here = self->ring_home.next;
......@@ -174,8 +265,9 @@ scan_gc_items(ccobject *self,int target)
return 0;
/* At this point we know that the ring only contains nodes from
persistent objects, plus our own home node. We can safely
assume this is a persistent object now we know it is not the home */
persistent objects, plus our own home node. We know this because
the ring lock is held. We can safely assume the current ring
node is a persistent object now we know it is not the home */
object = object_from_ring(self, here, "scan_gc_items");
if (!object)
return -1;
......@@ -190,6 +282,8 @@ scan_gc_items(ccobject *self,int target)
* so that we can follow the link after the ghosted object is
* removed from the ring (via ghostify()).
*/
/* FIXME: This needs to be changed back to a placeholder */
CPersistentRing *next = here->next;
ENGINE_NOISE("G");
......@@ -420,6 +514,8 @@ cc_lru_items(ccobject *self, PyObject *args)
return NULL;
if (self->ring_lock) {
/* When the ring lock is held, we have no way of know which ring nodes
belong to persistent objects, and which a placeholders. */
PyErr_SetString(PyExc_ValueError,
".lru_items() is unavailable during garbage collection");
return NULL;
......@@ -498,6 +594,8 @@ cc_oid_unreferenced(ccobject *self, PyObject *args)
#ifdef Py_TRACE_REFS
#error "this code path has not been tested - Toby Dickenson"
/* not tested, but it should still work. I would appreciate
reports of success */
_Py_NewReference(v);
/* it may be a problem that v->ob_type is still NULL? */
#else
......@@ -682,12 +780,14 @@ cc_add_item(ccobject *self, PyObject *key, PyObject *v)
"Cache values must be persistent objects.");
return -1;
}
/* Is this set of tests necessary? */
class = (PyExtensionClass *)(v->ob_type);
if (!((class->class_flags & PERSISTENT_TYPE_FLAG)
&& v->ob_type->tp_basicsize >= sizeof(cPersistentObject))) {
PyErr_SetString(PyExc_ValueError,
"Cache values must be persistent objects.");
/* Must be either persistent classes (ie ZClasses), or instances
of persistent classes (ie Python classeses that derive from
Persistence.Persistent, BTrees, etc) */
return -1;
}
......@@ -698,7 +798,8 @@ cc_add_item(ccobject *self, PyObject *key, PyObject *v)
if (oid == NULL)
return -1;
/* XXX key and oid should both be PyString objects */
/* XXX key and oid should both be PyString objects.
May be helpful to check this. */
if (PyObject_Cmp(key, oid, &result) < 0) {
Py_DECREF(oid);
return -1;
......
trunk/src/persistent/cPickleCache.c
View file @ 084b834d
......@@ -12,10 +12,85 @@
****************************************************************************/
/*
Objects are stored under three different regimes:
Regime 1: Persistent Classes
Persistent Classes are part of ZClasses. They are stored in the
self->data dictionary, and are never garbage collected.
The klass_items() method returns a sequence of (oid,object) tuples
for every Persistent Class, which should make it possible to
implement garbage collection in Python if necessary.
Regime 2: Ghost Objects
There is no benefit to keeping a ghost object which has no
external references, therefore a weak reference scheme is
used to ensure that ghost objects are removed from memory
as soon as possible, when the last external reference is lost.
Ghost objects are stored in the self->data dictionary. Normally
a dictionary keeps a strong reference on its values, however
this reference count is 'stolen'.
This weak reference scheme leaves a dangling reference, in the
dictionary, when the last external reference is lost. To clean up
this dangling reference the persistent object dealloc function
calls self->cache->_oid_unreferenced(self->oid). The cache looks
up the oid in the dictionary, ensures it points to an object whose
reference count is zero, then removes it from the dictionary. Before
removing the object from the dictionary it must temporarily resurrect
the object in much the same way that class instances are resurrected
before their __del__ is called.
Since ghost objects are stored under a different regime to
non-ghost objects, an extra ghostify function in cPersistenceAPI
replaces self->state=GHOST_STATE assignments that were common in
other persistent classes (such as BTrees).
Regime 3: Non-Ghost Objects
Non-ghost objects are stored in two data structures. Firstly, in
the dictionary along with everything else, with a *strong* reference.
Secondly, they are stored in a doubly-linked-list which encodes
the order in which these objects have been most recently used.
The doubly-link-list nodes contain next and previous pointers
linking together the cache and all non-ghost persistent objects.
The node embedded in the cache is the home position. On every
attribute access a non-ghost object will relink itself just
behind the home position in the ring. Objects accessed least
recently will eventually find themselves positioned after
the home position.
Occasionally other nodes are temporarily inserted in the ring
as position markers. The cache contains a ring_lock flag which
must be set and unset before and after doing so. Only if the flag
is unset can the cache assume that all nodes are either his own
home node, or nodes from persistent objects. This assumption is
useful during the garbage collection process.
The number of non-ghost objects is counted in self->non_ghost_count.
The garbage collection process consists of traversing the ring, and
deactivating (that is, turning into a ghost) every object until
self->non_ghost_count is down to the target size, or until it
reaches the home position again.
Note that objects in the sticky or changed states are still kept
in the ring, however they can not be deactivated. The garbage
collection process must skip such objects, rather than deactivating
them.
*/
static char cPickleCache_doc_string[] =
"Defines the PickleCache used by ZODB Connection objects.\n"
"\n"
"$Id: cPickleCache.c,v 1.50 2002/04/03 00:03:32 jeremy Exp $\n";
"$Id: cPickleCache.c,v 1.51 2002/04/03 17:00:44 htrd Exp $\n";
#define ASSIGN(V,E) {PyObject *__e; __e=(E); Py_XDECREF(V); (V)=__e;}
#define UNLESS(E) if(!(E))
......@@ -30,9 +105,10 @@ static char cPickleCache_doc_string[] =
static PyObject *py__p_oid, *py_reload, *py__p_jar, *py__p_changed;
/* define this for extra debugging checks, and lousy performance */
/* Are any of these checks necessary in production code? How do we
decide when to disable it?
/* define this for extra debugging checks, and lousy performance.
Not really necessary in production code... disable this before
release, providing noone has been reporting and RuntimeErrors
that it uses to report problems.
*/
#define MUCH_RING_CHECKING 1
......@@ -44,23 +120,36 @@ static PyObject *py__p_oid, *py_reload, *py__p_jar, *py__p_changed;
#define ENGINE_NOISE(A) ((void)A)
#endif
/* This object is the pickle cache. The layout of this struct is the same
* as the start of ccobject_head in cPersistence.c
* XXX Why do they need to have the same layouts?
*/
/* This object is the pickle cache. The CACHE_HEAD macro guarantees that
layout of this struct is the same as the start of ccobject_head in
cPersistence.c */
typedef struct {
CACHE_HEAD
int klass_count; /* XXX for ZClass support? */
int klass_count; /* count of persistent classes */
PyObject *data; /* oid -> object dict */
PyObject *jar; /* Connection object */
PyObject *setklassstate; /* ??? */
int cache_size; /* number of items in cache */
int ring_lock; /* ??? */
/* XXX Settable from Python, this appears to be a ratio controlling how
* the cache gets gradually smaller. It is probably an error for this
* to be negative.
*/
int cache_size; /* target number of items in cache */
/* Most of the time the ring contains only:
* many nodes corresponding to persistent objects
* one 'home' node from the cache.
In some cases it is handy to temporarily add other types
of node into the ring as placeholders. 'ring_lock' is a boolean
indicating that someone has already done this. Currently this
is only used by the garbage collection code. */
int ring_lock;
/* 'cache_drain_resistance' controls how quickly the cache size will drop
when it is smaller than the configured size. A value of zero means it will
not drop below the configured size (suitable for most caches). Otherwise,
it will remove cache_non_ghost_count/cache_drain_resistance items from
the cache every time (suitable for rarely used caches, such as those
associated with Zope versions. */
int cache_drain_resistance;
} ccobject;
static int present_in_ring(ccobject *self, CPersistentRing *target);
......@@ -127,6 +216,8 @@ object_from_ring(ccobject *self, CPersistentRing *here, const char *context)
static int
scan_gc_items(ccobject *self,int target)
{
/* This function must only be called with the ring lock held */
cPersistentObject *object;
int error;
CPersistentRing *here = self->ring_home.next;
......@@ -174,8 +265,9 @@ scan_gc_items(ccobject *self,int target)
return 0;
/* At this point we know that the ring only contains nodes from
persistent objects, plus our own home node. We can safely
assume this is a persistent object now we know it is not the home */
persistent objects, plus our own home node. We know this because
the ring lock is held. We can safely assume the current ring
node is a persistent object now we know it is not the home */
object = object_from_ring(self, here, "scan_gc_items");
if (!object)
return -1;
......@@ -190,6 +282,8 @@ scan_gc_items(ccobject *self,int target)
* so that we can follow the link after the ghosted object is
* removed from the ring (via ghostify()).
*/
/* FIXME: This needs to be changed back to a placeholder */
CPersistentRing *next = here->next;
ENGINE_NOISE("G");
......@@ -420,6 +514,8 @@ cc_lru_items(ccobject *self, PyObject *args)
return NULL;
if (self->ring_lock) {
/* When the ring lock is held, we have no way of know which ring nodes
belong to persistent objects, and which a placeholders. */
PyErr_SetString(PyExc_ValueError,
".lru_items() is unavailable during garbage collection");
return NULL;
......@@ -498,6 +594,8 @@ cc_oid_unreferenced(ccobject *self, PyObject *args)
#ifdef Py_TRACE_REFS
#error "this code path has not been tested - Toby Dickenson"
/* not tested, but it should still work. I would appreciate
reports of success */
_Py_NewReference(v);
/* it may be a problem that v->ob_type is still NULL? */
#else
......@@ -682,12 +780,14 @@ cc_add_item(ccobject *self, PyObject *key, PyObject *v)
"Cache values must be persistent objects.");
return -1;
}
/* Is this set of tests necessary? */
class = (PyExtensionClass *)(v->ob_type);
if (!((class->class_flags & PERSISTENT_TYPE_FLAG)
&& v->ob_type->tp_basicsize >= sizeof(cPersistentObject))) {
PyErr_SetString(PyExc_ValueError,
"Cache values must be persistent objects.");
/* Must be either persistent classes (ie ZClasses), or instances
of persistent classes (ie Python classeses that derive from
Persistence.Persistent, BTrees, etc) */
return -1;
}
......@@ -698,7 +798,8 @@ cc_add_item(ccobject *self, PyObject *key, PyObject *v)
if (oid == NULL)
return -1;
/* XXX key and oid should both be PyString objects */
/* XXX key and oid should both be PyString objects.
May be helpful to check this. */
if (PyObject_Cmp(key, oid, &result) < 0) {
Py_DECREF(oid);
return -1;
......
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