Avoid "immortal" dynamic memory allocations.

Statically allocating the storage and then lazily constructing the objects
(in onces) avoids global constructors and the false positives (thanks,
Valgrind) about memory leaks at program termination.

Fixes #28, #190, #377, #387.

Change-Id: I5b3eaf5d743a4723212c5a7461c280d99a0384ac
Reviewed-on: https://code-review.googlesource.com/c/re2/+/60850
Reviewed-by: Perry Lorier <[email protected]>
Reviewed-by: Paul Wankadia <[email protected]>

re2/re2.cc

@@ -65,11 +65,30 @@ RE2::Options::Options(RE2::CannedOptions opt)
     one_line_(false) {
 }
 
-// static empty objects for use as const references.
-// To avoid global constructors, allocated in RE2::Init().
-static const std::string* empty_string;
-static const std::map<std::string, int>* empty_named_groups;
-static const std::map<int, std::string>* empty_group_names;
+// Empty objects for use as const references.
+// Statically allocating the storage and then
+// lazily constructing the objects (in a once
+// in RE2::Init()) avoids global constructors
+// and the false positives (thanks, Valgrind)
+// about memory leaks at program termination.
+struct EmptyStorage {
+  std::string empty_string;
+  std::map<std::string, int> empty_named_groups;
+  std::map<int, std::string> empty_group_names;
+};
+alignas(EmptyStorage) static char empty_storage[sizeof(EmptyStorage)];
+
+static inline std::string* empty_string() {
+  return &reinterpret_cast<EmptyStorage*>(empty_storage)->empty_string;
+}
+
+static inline std::map<std::string, int>* empty_named_groups() {
+  return &reinterpret_cast<EmptyStorage*>(empty_storage)->empty_named_groups;
+}
+
+static inline std::map<int, std::string>* empty_group_names() {
+  return &reinterpret_cast<EmptyStorage*>(empty_storage)->empty_group_names;
+}
 
 // Converts from Regexp error code to RE2 error code.
 // Maybe some day they will diverge.  In any event, this
@@ -180,17 +199,15 @@ int RE2::Options::ParseFlags() const {
 void RE2::Init(const StringPiece& pattern, const Options& options) {
   static std::once_flag empty_once;
   std::call_once(empty_once, []() {
-    empty_string = new std::string;
-    empty_named_groups = new std::map<std::string, int>;
-    empty_group_names = new std::map<int, std::string>;
+    (void) new (empty_storage) EmptyStorage;
   });
 
   pattern_ = new std::string(pattern);
   options_.Copy(options);
   entire_regexp_ = NULL;
   suffix_regexp_ = NULL;
-  error_ = empty_string;
-  error_arg_ = empty_string;
+  error_ = empty_string();
+  error_arg_ = empty_string();
 
   num_captures_ = -1;
   error_code_ = NoError;
@@ -275,15 +292,15 @@ re2::Prog* RE2::ReverseProg() const {
 }
 
 RE2::~RE2() {
-  if (group_names_ != empty_group_names)
+  if (group_names_ != empty_group_names())
     delete group_names_;
-  if (named_groups_ != empty_named_groups)
+  if (named_groups_ != empty_named_groups())
     delete named_groups_;
   delete rprog_;
   delete prog_;
-  if (error_arg_ != empty_string)
+  if (error_arg_ != empty_string())
     delete error_arg_;
-  if (error_ != empty_string)
+  if (error_ != empty_string())
     delete error_;
   if (suffix_regexp_)
     suffix_regexp_->Decref();
@@ -369,7 +386,7 @@ const std::map<std::string, int>& RE2::NamedCapturingGroups() const {
     if (re->suffix_regexp_ != NULL)
       re->named_groups_ = re->suffix_regexp_->NamedCaptures();
     if (re->named_groups_ == NULL)
-      re->named_groups_ = empty_named_groups;
+      re->named_groups_ = empty_named_groups();
   }, this);
   return *named_groups_;
 }
@@ -380,7 +397,7 @@ const std::map<int, std::string>& RE2::CapturingGroupNames() const {
     if (re->suffix_regexp_ != NULL)
       re->group_names_ = re->suffix_regexp_->CaptureNames();
     if (re->group_names_ == NULL)
-      re->group_names_ = empty_group_names;
+      re->group_names_ = empty_group_names();
   }, this);
   return *group_names_;
 }

re2/regexp.cc

@@ -74,35 +74,45 @@ bool Regexp::QuickDestroy() {
   return false;
 }
 
-// Lazily allocated.
-static Mutex* ref_mutex;
-static std::map<Regexp*, int>* ref_map;
+// Similar to EmptyStorage in re2.cc.
+struct RefStorage {
+  Mutex ref_mutex;
+  std::map<Regexp*, int> ref_map;
+};
+alignas(RefStorage) static char ref_storage[sizeof(RefStorage)];
+
+static inline Mutex* ref_mutex() {
+  return &reinterpret_cast<RefStorage*>(ref_storage)->ref_mutex;
+}
+
+static inline std::map<Regexp*, int>* ref_map() {
+  return &reinterpret_cast<RefStorage*>(ref_storage)->ref_map;
+}
 
 int Regexp::Ref() {
   if (ref_ < kMaxRef)
     return ref_;
 
-  MutexLock l(ref_mutex);
-  return (*ref_map)[this];
+  MutexLock l(ref_mutex());
+  return (*ref_map())[this];
 }
 
 // Increments reference count, returns object as convenience.
 Regexp* Regexp::Incref() {
   if (ref_ >= kMaxRef-1) {
     static std::once_flag ref_once;
     std::call_once(ref_once, []() {
-      ref_mutex = new Mutex;
-      ref_map = new std::map<Regexp*, int>;
+      (void) new (ref_storage) RefStorage;
     });
 
     // Store ref count in overflow map.
-    MutexLock l(ref_mutex);
+    MutexLock l(ref_mutex());
     if (ref_ == kMaxRef) {
       // already overflowed
-      (*ref_map)[this]++;
+      (*ref_map())[this]++;
     } else {
       // overflowing now
-      (*ref_map)[this] = kMaxRef;
+      (*ref_map())[this] = kMaxRef;
       ref_ = kMaxRef;
     }
     return this;
@@ -116,13 +126,13 @@ Regexp* Regexp::Incref() {
 void Regexp::Decref() {
   if (ref_ == kMaxRef) {
     // Ref count is stored in overflow map.
-    MutexLock l(ref_mutex);
-    int r = (*ref_map)[this] - 1;
+    MutexLock l(ref_mutex());
+    int r = (*ref_map())[this] - 1;
     if (r < kMaxRef) {
       ref_ = static_cast<uint16_t>(r);
-      ref_map->erase(this);
+      ref_map()->erase(this);
     } else {
-      (*ref_map)[this] = r;
+      (*ref_map())[this] = r;
     }
     return;
   }