core: add reusable slab allocator

bnoordhuis · bnoordhuis · commit 08032efed00b · 2012-03-30T21:24:02.000+02:00
diff --git a/node.gyp b/node.gyp
@@ -84,6 +84,7 @@
         'src/node_zlib.cc',
         'src/pipe_wrap.cc',
         'src/stream_wrap.cc',
+        'src/slab_allocator.cc',
         'src/tcp_wrap.cc',
         'src/timer_wrap.cc',
         'src/tty_wrap.cc',
@@ -107,6 +108,7 @@
         'src/node_version.h',
         'src/pipe_wrap.h',
         'src/req_wrap.h',
+        'src/slab_allocator.h',
         'src/stream_wrap.h',
         'src/v8_typed_array.h',
         'deps/http_parser/http_parser.h',
diff --git a/src/slab_allocator.cc b/src/slab_allocator.cc
@@ -0,0 +1,127 @@
+// Copyright Joyent, Inc. and other Node contributors.
+//
+// Permission is hereby granted, free of charge, to any person obtaining a
+// copy of this software and associated documentation files (the
+// "Software"), to deal in the Software without restriction, including
+// without limitation the rights to use, copy, modify, merge, publish,
+// distribute, sublicense, and/or sell copies of the Software, and to permit
+// persons to whom the Software is furnished to do so, subject to the
+// following conditions:
+//
+// The above copyright notice and this permission notice shall be included
+// in all copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
+// OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+// MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN
+// NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM,
+// DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR
+// OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE
+// USE OR OTHER DEALINGS IN THE SOFTWARE.
+
+#include "v8.h"
+#include "node.h"
+#include "node_buffer.h"
+#include "slab_allocator.h"
+#include <stdio.h>
+#include <stdlib.h>
+#include <assert.h>
+
+
+using v8::Handle;
+using v8::HandleScope;
+using v8::Integer;
+using v8::Local;
+using v8::Null;
+using v8::Object;
+using v8::Persistent;
+using v8::String;
+using v8::Value;
+
+
+namespace node {
+
+SlabAllocator::SlabAllocator(unsigned int size) {
+  size_ = ROUND_UP(size ? size : 1, 8192);
+  initialized_ = false;
+}
+
+
+SlabAllocator::~SlabAllocator() {
+  if (!initialized_) return;
+  slab_sym_.Clear();
+  slab_sym_.Dispose();
+  slab_.Clear();
+  slab_.Dispose();
+}
+
+
+void SlabAllocator::Initialize() {
+  HandleScope scope;
+  char sym[256];
+  snprintf(sym, sizeof(sym), "slab_%p", this); // namespace object key
+  offset_ = 0;
+  last_ptr_ = NULL;
+  initialized_ = true;
+  slab_sym_ = Persistent<String>::New(String::New(sym));
+}
+
+
+static Local<Object> NewSlab(unsigned int size) {
+  HandleScope scope;
+  Local<Value> arg = Integer::NewFromUnsigned(ROUND_UP(size, 16));
+  Local<Object> buf = Buffer::constructor_template
+                      ->GetFunction()
+                      ->NewInstance(1, &arg);
+  return scope.Close(buf);
+}
+
+
+char* SlabAllocator::Allocate(Handle<Object> obj, unsigned int size) {
+  HandleScope scope;
+
+  assert(!obj.IsEmpty());
+
+  if (size == 0) return NULL;
+  if (!initialized_) Initialize();
+
+  if (size > size_) {
+    Local<Object> buf = NewSlab(size);
+    obj->SetHiddenValue(slab_sym_, buf);
+    return Buffer::Data(buf);
+  }
+
+  if (slab_.IsEmpty() || offset_ + size > size_) {
+    slab_.Clear();
+    slab_.Dispose();
+    slab_ = Persistent<Object>::New(NewSlab(size_));
+    offset_ = 0;
+    last_ptr_ = NULL;
+  }
+
+  obj->SetHiddenValue(slab_sym_, slab_);
+  last_ptr_ = Buffer::Data(slab_) + offset_;
+  offset_ += size;
+
+  return last_ptr_;
+}
+
+
+Local<Object> SlabAllocator::Shrink(Handle<Object> obj,
+                                    char* ptr,
+                                    unsigned int size) {
+  HandleScope scope;
+  Local<Value> slab_v = obj->GetHiddenValue(slab_sym_);
+  obj->SetHiddenValue(slab_sym_, Null());
+  assert(!slab_v.IsEmpty());
+  assert(slab_v->IsObject());
+  Local<Object> slab = slab_v->ToObject();
+  if (ptr && ptr == last_ptr_) {
+    last_ptr_ = NULL;
+    offset_ = ptr - Buffer::Data(slab) + ROUND_UP(size, 16);
+  }
+  return scope.Close(slab);
+}
+
+
+} // namespace node
diff --git a/src/slab_allocator.h b/src/slab_allocator.h
@@ -0,0 +1,49 @@
+// Copyright Joyent, Inc. and other Node contributors.
+//
+// Permission is hereby granted, free of charge, to any person obtaining a
+// copy of this software and associated documentation files (the
+// "Software"), to deal in the Software without restriction, including
+// without limitation the rights to use, copy, modify, merge, publish,
+// distribute, sublicense, and/or sell copies of the Software, and to permit
+// persons to whom the Software is furnished to do so, subject to the
+// following conditions:
+//
+// The above copyright notice and this permission notice shall be included
+// in all copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
+// OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+// MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN
+// NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM,
+// DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR
+// OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE
+// USE OR OTHER DEALINGS IN THE SOFTWARE.
+
+#include "v8.h"
+
+namespace node {
+
+class SlabAllocator {
+public:
+  SlabAllocator(unsigned int size = 10485760); // default to 10M
+  ~SlabAllocator();
+
+  // allocate memory from slab, attaches the slice to `obj`
+  char* Allocate(v8::Handle<v8::Object> obj, unsigned int size);
+
+  // return excess memory to the slab, returns a handle to the parent buffer
+  v8::Local<v8::Object> Shrink(v8::Handle<v8::Object> obj,
+                               char* ptr,
+                               unsigned int size);
+
+private:
+  void Initialize();
+  bool initialized_;
+  v8::Persistent<v8::Object> slab_;
+  v8::Persistent<v8::String> slab_sym_;
+  unsigned int offset_;
+  unsigned int size_;
+  char* last_ptr_;
+};
+
+} // namespace node
