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Cleanup of LRU cache implementation

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Switch to CRTP from virtual functions and improve ownership semantics.
It's no longer necessary for clients to use new and delete.
This commit is contained in:
ridiculousfish 2017-01-27 12:18:16 -08:00
parent 61f272495d
commit e52a04e341
5 changed files with 191 additions and 187 deletions
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31
src/autoload.cpp
View file

@ -57,13 +57,12 @@ autoload_t::autoload_t(const wcstring &env_var_name_var, const builtin_script_t
autoload_t::~autoload_t() { pthread_mutex_destroy(&lock); }
void autoload_t::node_was_evicted(autoload_function_t *node) {
void autoload_t::entry_was_evicted(wcstring key, autoload_function_t node) {
// This should only ever happen on the main thread.
ASSERT_IS_MAIN_THREAD();
// Tell ourselves that the command was removed if it was loaded.
if (node->is_loaded) this->command_removed(node->key);
delete node;
if (node.is_loaded) this->command_removed(std::move(key));
}
int autoload_t::unload(const wcstring &cmd) { return this->evict_node(cmd); }
@ -130,7 +129,7 @@ static bool script_name_precedes_script_name(const builtin_script_t &script1,
/// Check whether the given command is loaded.
bool autoload_t::has_tried_loading(const wcstring &cmd) {
scoped_lock locker(lock);
autoload_function_t *func = this->get_node(cmd);
autoload_function_t *func = this->get(cmd);
return func != NULL;
}
@ -144,14 +143,16 @@ static bool is_stale(const autoload_function_t *func) {
autoload_function_t *autoload_t::get_autoloaded_function_with_creation(const wcstring &cmd,
bool allow_eviction) {
ASSERT_IS_LOCKED(lock);
autoload_function_t *func = this->get_node(cmd);
autoload_function_t *func = this->get(cmd);
if (!func) {
func = new autoload_function_t(cmd);
bool added;
if (allow_eviction) {
this->add_node(func);
added = this->insert(cmd, autoload_function_t(false));
} else {
this->add_node_without_eviction(func);
added = this->insert_no_eviction(cmd, autoload_function_t(false));
}
func = this->get(cmd);
assert(func);
}
return func;
}
@ -188,7 +189,7 @@ bool autoload_t::locate_file_and_maybe_load_it(const wcstring &cmd, bool really_
{
bool allow_stale_functions = !reload;
scoped_lock locker(lock);
autoload_function_t *func = this->get_node(cmd); // get the function
autoload_function_t *func = this->get(cmd); // get the function
// If we can use this function, return whether we were able to access it.
if (use_cached(func, really_load, allow_stale_functions)) {
@ -243,7 +244,7 @@ bool autoload_t::locate_file_and_maybe_load_it(const wcstring &cmd, bool really_
// Now we're actually going to take the lock.
scoped_lock locker(lock);
autoload_function_t *func = this->get_node(cmd);
autoload_function_t *func = this->get(cmd);
// Generate the source if we need to load it.
bool need_to_load_function =
@ -286,15 +287,15 @@ bool autoload_t::locate_file_and_maybe_load_it(const wcstring &cmd, bool really_
if (!found_file && !has_script_source) {
scoped_lock locker(lock);
// Generate a placeholder.
autoload_function_t *func = this->get_node(cmd);
autoload_function_t *func = this->get(cmd);
if (!func) {
func = new autoload_function_t(cmd);
func->is_placeholder = true;
if (really_load) {
this->add_node(func);
this->insert(cmd, autoload_function_t(true));
} else {
this->add_node_without_eviction(func);
this->insert(cmd, autoload_function_t(true));
}
func = this->get(cmd);
assert(func);
}
func->access.last_checked = time(NULL);
}

21
src/autoload.h
View file

@ -25,12 +25,11 @@ struct file_access_attempt_t {
};
file_access_attempt_t access_file(const wcstring &path, int mode);
struct autoload_function_t : public lru_node_t {
explicit autoload_function_t(const wcstring &key)
: lru_node_t(key),
access(),
struct autoload_function_t {
explicit autoload_function_t(bool placeholder)
: access(),
is_loaded(false),
is_placeholder(false),
is_placeholder(placeholder),
is_internalized(false) {}
/// The last access attempt recorded
@ -52,7 +51,7 @@ struct builtin_script_t {
class env_vars_snapshot_t;
/// Class representing a path from which we can autoload and the autoloaded contents.
class autoload_t : private lru_cache_t<autoload_function_t> {
class autoload_t : public lru_cache_t<autoload_t, autoload_function_t> {
private:
/// Lock for thread safety.
pthread_mutex_t lock;
@ -70,13 +69,11 @@ class autoload_t : private lru_cache_t<autoload_function_t> {
/// This is here to help prevent recursion.
std::set<wcstring> is_loading_set;
void remove_all_functions(void) { this->evict_all_nodes(); }
void remove_all_functions() { this->evict_all_nodes(); }
bool locate_file_and_maybe_load_it(const wcstring &cmd, bool really_load, bool reload,
const wcstring_list_t &path_list);
virtual void node_was_evicted(autoload_function_t *node);
autoload_function_t *get_autoloaded_function_with_creation(const wcstring &cmd,
bool allow_eviction);
@ -85,7 +82,11 @@ class autoload_t : private lru_cache_t<autoload_function_t> {
virtual void command_removed(const wcstring &cmd) { UNUSED(cmd); }
public:
/// Create an autoload_t for the given environment variable name.
// CRTP override
void entry_was_evicted(wcstring key, autoload_function_t node);
// Create an autoload_t for the given environment variable name.
autoload_t(const wcstring &env_var_name_var, const builtin_script_t *scripts,
size_t script_count);

40
src/fish_tests.cpp
View file

@ -1122,20 +1122,14 @@ static void test_escape_sequences(void) {
err(L"test_escape_sequences failed on line %d\n", __LINE__);
}
class lru_node_test_t : public lru_node_t {
class test_lru_t : public lru_cache_t<test_lru_t, int> {
public:
explicit lru_node_test_t(const wcstring &tmp) : lru_node_t(tmp) {}
};
test_lru_t() : lru_cache_t<test_lru_t, int>(16) {}
class test_lru_t : public lru_cache_t<lru_node_test_t> {
public:
test_lru_t() : lru_cache_t<lru_node_test_t>(16) {}
std::vector<std::pair<wcstring, int>> evicted;
std::vector<lru_node_test_t *> evicted_nodes;
virtual void node_was_evicted(lru_node_test_t *node) {
do_test(find(evicted_nodes.begin(), evicted_nodes.end(), node) == evicted_nodes.end());
evicted_nodes.push_back(node);
void entry_was_evicted(wcstring key, int val) {
evicted.push_back({key, val});
}
};
@ -1143,24 +1137,18 @@ static void test_lru(void) {
say(L"Testing LRU cache");
test_lru_t cache;
std::vector<lru_node_test_t *> expected_evicted;
size_t total_nodes = 20;
for (size_t i = 0; i < total_nodes; i++) {
do_test(cache.size() == std::min(i, (size_t)16));
lru_node_test_t *node = new lru_node_test_t(to_string(i));
if (i < 4) expected_evicted.push_back(node);
std::vector<std::pair<wcstring, int>> expected_evicted;
int total_nodes = 20;
for (int i = 0; i < total_nodes; i++) {
do_test(cache.size() == size_t(std::min(i, 16)));
if (i < 4) expected_evicted.push_back({to_string(i), i});
// Adding the node the first time should work, and subsequent times should fail.
do_test(cache.add_node(node));
do_test(!cache.add_node(node));
do_test(cache.insert(to_string(i), i));
do_test(!cache.insert(to_string(i), i+1));
}
do_test(cache.evicted_nodes == expected_evicted);
do_test(cache.evicted == expected_evicted);
cache.evict_all_nodes();
do_test(cache.evicted_nodes.size() == total_nodes);
while (!cache.evicted_nodes.empty()) {
lru_node_t *node = cache.evicted_nodes.back();
cache.evicted_nodes.pop_back();
delete node;
}
do_test(cache.evicted.size() == size_t(total_nodes));
}
/// Perform parameter expansion and test if the output equals the zero-terminated parameter list

28
src/history.cpp
View file

@ -142,23 +142,22 @@ static bool history_file_lock(int fd, int lock_type) {
/// Our LRU cache is used for restricting the amount of history we have, and limiting how long we
/// order it.
class history_lru_node_t : public lru_node_t {
class history_lru_item_t {
public:
wcstring text;
time_t timestamp;
path_list_t required_paths;
explicit history_lru_node_t(const history_item_t &item)
: lru_node_t(item.str()),
explicit history_lru_item_t(const history_item_t &item)
: text(item.str()),
timestamp(item.timestamp()),
required_paths(item.get_required_paths()) {}
};
class history_lru_cache_t : public lru_cache_t<history_lru_node_t> {
protected:
/// Override to delete evicted nodes.
virtual void node_was_evicted(history_lru_node_t *node) { delete node; }
class history_lru_cache_t : public lru_cache_t<history_lru_cache_t, history_lru_item_t> {
typedef lru_cache_t<history_lru_cache_t, history_lru_item_t> super;
public:
explicit history_lru_cache_t(size_t max) : lru_cache_t<history_lru_node_t>(max) {}
using super::super;
/// Function to add a history item.
void add_item(const history_item_t &item) {
@ -167,10 +166,10 @@ class history_lru_cache_t : public lru_cache_t<history_lru_node_t> {
// See if it's in the cache. If it is, update the timestamp. If not, we create a new node
// and add it. Note that calling get_node promotes the node to the front.
history_lru_node_t *node = this->get_node(item.str());
wcstring key = item.str();
history_lru_item_t *node = this->get(key);
if (node == NULL) {
node = new history_lru_node_t(item);
this->add_node(node);
this->insert(std::move(key), history_lru_item_t(item));
} else {
node->timestamp = std::max(node->timestamp, item.timestamp());
// What to do about paths here? Let's just ignore them.
@ -1248,8 +1247,9 @@ bool history_t::save_internal_via_rewrite() {
bool errored = false;
history_output_buffer_t buffer;
for (history_lru_cache_t::iterator iter = lru.begin(); iter != lru.end(); ++iter) {
const history_lru_node_t *node = *iter;
append_yaml_to_buffer(node->key, node->timestamp, node->required_paths, &buffer);
const wcstring &text = (*iter).first;
const history_lru_item_t &item = (*iter).second;
append_yaml_to_buffer(text, item.timestamp, item.required_paths, &buffer);
if (buffer.output_size() >= HISTORY_OUTPUT_BUFFER_SIZE &&
!buffer.flush_to_fd(out_fd)) {
errored = true;

258
src/lru.h
View file

@ -4,190 +4,204 @@
#include <assert.h>
#include <wchar.h>
#include <list>
#include <map>
#include <set>
#include "common.h"
/// A predicate to compare dereferenced pointers.
struct dereference_less_t {
template <typename ptr_t>
bool operator()(ptr_t p1, ptr_t p2) const {
return *p1 < *p2;
}
};
class lru_node_t {
template <class T>
friend class lru_cache_t;
/// Our linked list pointer.
lru_node_t *prev, *next;
public:
/// The key used to look up in the cache.
const wcstring key;
/// Constructor.
explicit lru_node_t(const wcstring &pkey) : prev(NULL), next(NULL), key(pkey) {}
/// Virtual destructor that does nothing for classes that inherit lru_node_t.
virtual ~lru_node_t() {}
/// operator< for std::set
bool operator<(const lru_node_t &other) const { return key < other.key; }
};
template <class node_type_t>
// Least-recently-used cache class
// This a map from wcstring to CONTENTS, that will evict entries when the count exceeds the maximum.
// It uses CRTP to inform clients when entries are evicted. This uses the classic LRU cache structure:
// a dictionary mapping keys to nodes, where the nodes also form a linked list. Our linked list is
// circular and has a sentinel node (the "mouth" - picture a snake swallowing its tail). This simplifies
// the logic: no pointer is ever NULL! It also works well with C++'s iterator since the sentinel node
// is a natural value for end(). Our nodes also have the unusual property of having a "back pointer":
// they store an iterator to the entry in the map containing the node. This allows us, given a node, to
// immediately locate the node and its key in the dictionary. This allows us to avoid duplicating the key
// in the node.
template <class DERIVED, class CONTENTS>
class lru_cache_t {
private:
/// Max node count. This may be (transiently) exceeded by add_node_without_eviction, which is
/// used from background threads.
struct lru_node_t;
typedef typename std::map<wcstring, lru_node_t>::iterator node_iter_t;
struct lru_link_t {
// Our doubly linked list
// The base class is used for the mouth only
lru_link_t *prev = NULL;
lru_link_t *next = NULL;
};
// The node type in our LRU cache
struct lru_node_t : public lru_link_t {
// No copying
lru_node_t(const lru_node_t &) = delete;
lru_node_t &operator=(const lru_node_t &) = delete;
lru_node_t(lru_node_t &&) = default;
// Our location in the map!
node_iter_t iter;
// The value from the client
CONTENTS value;
explicit lru_node_t(CONTENTS v) :
value(std::move(v))
{}
};
// Max node count. This may be (transiently) exceeded by add_node_without_eviction, which is
// used from background threads.
const size_t max_node_count;
/// Count of nodes.
size_t node_count;
// All of our nodes
// Note that our linked list contains pointers to these nodes in the map
// We are dependent on the iterator-noninvalidation guarantees of std::map
std::map<wcstring, lru_node_t> node_map;
/// The set of nodes.
typedef std::set<lru_node_t *, dereference_less_t> node_set_t;
node_set_t node_set;
// Head of the linked list
// The list is circular!
// If "empty" the mouth just points at itself.
lru_link_t mouth;
void promote_node(node_type_t *node) {
// We should never promote the mouth.
// Take a node and move it to the front of the list
void promote_node(lru_node_t *node) {
assert(node != &mouth);
// First unhook us.
// First unhook us
node->prev->next = node->next;
node->next->prev = node->prev;
// Put us after the mouth.
// Put us after the mouth
node->next = mouth.next;
node->next->prev = node;
node->prev = &mouth;
mouth.next = node;
}
void evict_node(node_type_t *condemned_node) {
// Remove the node
void evict_node(lru_node_t *node) {
assert(node != &mouth);
// We should never evict the mouth.
assert(condemned_node != NULL && condemned_node != &mouth);
assert(node != NULL && node->iter != this->node_map.end());
// Remove it from the linked list.
condemned_node->prev->next = condemned_node->next;
condemned_node->next->prev = condemned_node->prev;
node->prev->next = node->next;
node->next->prev = node->prev;
// Remove us from the set.
node_set.erase(condemned_node);
node_count--;
// Pull out our key and value
wcstring key = std::move(node->iter->first);
CONTENTS value(std::move(node->value));
// Tell ourselves.
this->node_was_evicted(condemned_node);
// Remove us from the map. This deallocates node!
node_map.erase(node->iter);
node = NULL;
// Tell ourselves what we did
DERIVED *dthis = static_cast<DERIVED *>(this);
dthis->entry_was_evicted(std::move(key), std::move(value));
}
void evict_last_node(void) { evict_node((node_type_t *)mouth.prev); }
// Evicts the last node
void evict_last_node() {
assert(mouth.prev != &mouth);
evict_node(static_cast<lru_node_t *>(mouth.prev));
}
static lru_node_t *get_previous(lru_node_t *node) { return node->prev; }
protected:
/// Head of the linked list.
lru_node_t mouth;
/// Overridable callback for when a node is evicted.
virtual void node_was_evicted(node_type_t *node) { UNUSED(node); }
// CRTP callback for when a node is evicted.
// Clients can implement this
void entry_was_evicted(wcstring key, CONTENTS value) {
USE(key);
USE(value);
}
public:
/// Constructor
explicit lru_cache_t(size_t max_size = 1024)
: max_node_count(max_size), node_count(0), mouth(wcstring()) {
// Hook up the mouth to itself: a one node circularly linked list!
mouth.prev = mouth.next = &mouth;
// Constructor
// Note our linked list is always circular!
explicit lru_cache_t(size_t max_size = 1024) : max_node_count(max_size) {
mouth.next = mouth.prev = &mouth;
}
/// Note that we do not evict nodes in our destructor (even though they typically need to be
/// deleted by their creator).
virtual ~lru_cache_t() {}
/// Returns the node for a given key, or NULL.
node_type_t *get_node(const wcstring &key) {
node_type_t *result = NULL;
// Construct a fake node as our key.
lru_node_t node_key(key);
// Look for it in the set.
node_set_t::iterator iter = node_set.find(&node_key);
// If we found a node, promote and return it.
if (iter != node_set.end()) {
result = static_cast<node_type_t *>(*iter);
promote_node(result);
// Returns the value for a given key, or NULL.
// This counts as a "use" and so promotes the node
CONTENTS *get(const wcstring &key) {
auto where = this->node_map.find(key);
if (where == this->node_map.end()) {
// not found
return NULL;
}
return result;
promote_node(&where->second);
return &where->second.value;
}
/// Evicts the node for a given key, returning true if a node was evicted.
// Evicts the node for a given key, returning true if a node was evicted.
bool evict_node(const wcstring &key) {
// Construct a fake node as our key.
lru_node_t node_key(key);
// Look for it in the set.
node_set_t::iterator iter = node_set.find(&node_key);
if (iter == node_set.end()) return false;
// Evict the given node.
evict_node(static_cast<node_type_t *>(*iter));
auto where = this->node_map.find(key);
if (where == this->node_map.end()) return false;
evict_node(&where->second);
return true;
}
/// Adds a node under the given key. Returns true if the node was added, false if the node was
/// not because a node with that key is already in the set.
bool add_node(node_type_t *node) {
// Add our node without eviction.
if (!this->add_node_without_eviction(node)) return false;
// Adds a node under the given key. Returns true if the node was added, false if the node was
// not because a node with that key is already in the set.
bool insert(wcstring key, CONTENTS value) {
if (! this->insert_no_eviction(std::move(key), std::move(value))) {
return false;
}
while (node_count > max_node_count) evict_last_node(); // evict
while (this->node_map.size() > max_node_count) {
evict_last_node();
}
return true;
}
/// Adds a node under the given key without triggering eviction. Returns true if the node was
/// added, false if the node was not because a node with that key is already in the set.
bool add_node_without_eviction(node_type_t *node) {
assert(node != NULL && node != &mouth);
// Adds a node under the given key without triggering eviction. Returns true if the node was
// added, false if the node was not because a node with that key is already in the set.
bool insert_no_eviction(wcstring key, CONTENTS value) {
// Try inserting; return false if it was already in the set.
if (!node_set.insert(node).second) return false;
auto iter_inserted = this->node_map.emplace(std::move(key), lru_node_t(std::move(value)));
if (! iter_inserted.second) {
// already present
return false;
}
// Tell the node where it is in the map
node_iter_t iter = iter_inserted.first;
lru_node_t *node = &iter->second;
node->iter = iter;
// Add the node after the mouth.
node->next = mouth.next;
node->next->prev = node;
node->prev = &mouth;
mouth.next = node;
// Update the count. This may push us over the maximum node count.
node_count++;
return true;
}
/// Counts nodes.
size_t size(void) { return node_count; }
// Number of entries
size_t size() { return this->node_map.size(); }
/// Evicts all nodes.
void evict_all_nodes(void) {
while (node_count > 0) {
while (this->size() > 0) {
evict_last_node();
}
}
/// Iterator for walking nodes, from least recently used to most.
// Iterator for walking nodes, from least recently used to most.
class iterator {
lru_node_t *node;
lru_link_t *node;
public:
explicit iterator(lru_node_t *val) : node(val) {}
void operator++() { node = lru_cache_t::get_previous(node); }
typedef std::pair<const wcstring &, const CONTENTS &> value_type;
explicit iterator(lru_link_t *val) : node(val) {}
void operator++() { node = node->prev; }
bool operator==(const iterator &other) { return node == other.node; }
bool operator!=(const iterator &other) { return !(*this == other); }
node_type_t *operator*() { return static_cast<node_type_t *>(node); }
value_type operator*() const {
const lru_node_t *dnode = static_cast<const lru_node_t *>(node);
const wcstring &key = dnode->iter->first;
return {key, dnode->value};
}
};
iterator begin() { return iterator(mouth.prev); }