Adds map_shm to open and mmap a region of POSIX shared memory.

README.md

@@ -59,6 +59,15 @@ You can also [msync()](http://pubs.opengroup.org/onlinepubs/9699919799/functions
 
 For compatibility, <b>mmap.map()</b> is an alias for <b>mmap()</b>
 
+If you wish to use [shared memory](http://en.wikipedia.org/wiki/Shared_memory#In_software) instead of a file, you can do so by calling: `mmap.map_shm(n_bytes, protection, flags, name, offset)` method.  All arguments are the same as <b>mmap()<b> except:
+
+<table>
+  <tr>
+    <td><i>name</i></td>
+    <td>Name of the <a href="http://man7.org/linux/man-pages/man7/shm_overview.7.html">POSIX shared memory</a> region.  <b>mmap.map_shm()</b> will create and/or attach to the region with read and write permissions, and truncate or expand the region to <b>size</b> bytes.</td>
+  </tr>
+</table>
+
 ## See Also
 
 * POSIX 1003.1 [mmap](http://pubs.opengroup.org/onlinepubs/9699919799/functions/mmap.html) and [msync](http://pubs.opengroup.org/onlinepubs/9699919799/functions/msync.html)

example/bloomwithshm.js

@@ -0,0 +1,82 @@
+fs = require("fs"),
+mmap = require("../index.js"); // obv. use require("mmap") if you lift
+HASH_FUNCTIONS=7; // how many hashes do you want?
+
+size = 1024*1024; // 1mb
+buffer = mmap.map_shm(size, mmap.PROT_READ|mmap.PROT_WRITE, mmap.MAP_SHARED, "/tmp/test_bloom");
+add(buffer, get_offsets("testing", buffer.length));
+console.log("check: ", check(buffer, get_offsets("testing", buffer.length)));
+
+
+/* basic bloom filter tricks */
+function get_offsets(string, buffer_size) {
+  var a = fnv_1a(string);
+  var b = fnv_1a_b(a);
+  var r = [];
+  var i = -1;
+  var x = a % buffer_size;
+  while (++i < HASH_FUNCTIONS) {
+    r.push(x < 0 ? (x + buffer_size) : x);
+    x = (x + b) % buffer_size;
+  }
+  return r;
+}
+function add(buffer, offsets) {
+  var i = -1;
+  var w = 0;
+  while (++i < HASH_FUNCTIONS) w += !!(buffer[ offsets[i] ]++);
+  if (HASH_FUNCTIONS == w) {
+    while (i-->0) --buffer[offsets[i]];
+    return true;
+  }
+  return false;
+}
+function check(buffer, offsets) {
+  var i = -1;
+  while (++i < HASH_FUNCTIONS)
+    if (!buffer[offsets[i]])
+        return false;
+  return true;
+}
+
+/* fowler-noll-vo (fnv) hashing */
+function fnv_1a(v) {
+  var n = v.length, a = 2166136261, c, d, i = -1;
+  while (++i < n) {
+    c = v.charCodeAt(i);
+    if (d = c & 0xff000000) {
+      a ^= d >> 24;
+      a += (a << 1) + (a << 4) + (a << 7) + (a << 8) + (a << 24);
+    }
+    if (d = c & 0xff0000) {
+      a ^= d >> 16;
+      a += (a << 1) + (a << 4) + (a << 7) + (a << 8) + (a << 24);
+    }
+    if (d = c & 0xff00) {
+      a ^= d >> 8;
+      a += (a << 1) + (a << 4) + (a << 7) + (a << 8) + (a << 24);
+    }
+    a ^= c & 0xff;
+    a += (a << 1) + (a << 4) + (a << 7) + (a << 8) + (a << 24);
+  }
+  /* from http://home.comcast.net/~bretm/hash/6.html */
+  a += a << 13;
+  a ^= a >> 7;
+  a += a << 3;
+  a ^= a >> 17;
+  a += a << 5;
+  return a & 0xffffffff;
+}
+
+/* one additional iteration of fnv, given a hash */
+function fnv_1a_b(a) {
+  a += (a << 1) + (a << 4) + (a << 7) + (a << 8) + (a << 24);
+  a += a << 13;
+  a ^= a >> 7;
+  a += a << 3;
+  a ^= a >> 17;
+  a += a << 5;
+  return a & 0xffffffff;
+}
+
+buffer.unlink();

index.js

@@ -21,5 +21,6 @@ function mmap_wrapper(size, protection, flags, fd, offset) {
 };
 for(var k in mmap) mmap_wrapper[k] = mmap[k];
 mmap_wrapper.map = mmap_wrapper;
+mmap_wrapper.map_shm = mmap.map_shm;
 
 module.exports = mmap_wrapper;

mmap.cpp

@@ -8,8 +8,12 @@
 static v8::Persistent<v8::String> length_symbol;
 static v8::Persistent<v8::String> unmap_symbol;
 static v8::Persistent<v8::String> sync_symbol;
+static v8::Persistent<v8::String> unlink_symbol;
+static v8::Persistent<v8::String> name_symbol;
 static v8::Persistent<v8::String> buffer_symbol;
 
+static v8::Persistent<v8::Function> map_symbol;
+
 static void Map_finalise(char *data, void*hint)
 {
 	munmap(data, (size_t)hint);
@@ -112,6 +116,52 @@ v8::Handle<v8::Value> Map(const v8::Arguments& args)
 	return scope.Close(actualBuffer);
 }
 
+v8::Handle<v8::Value> Unlink(const v8::Arguments& args)
+{
+	v8::HandleScope scope;
+	v8::String::Utf8Value name(args.This()->GetHiddenValue(name_symbol)->ToString());
+	if (shm_unlink(*name) < 0)
+	{
+		return v8::ThrowException(node::ErrnoException(errno, "unlink", ""));
+	}
+	return v8::True();
+}
+
+v8::Handle<v8::Value> MapShm(const v8::Arguments& args)
+{
+	v8::HandleScope scope;
+
+	if (args.Length() <= 3)
+	{
+		return v8::ThrowException(
+			v8::Exception::Error(
+				v8::String::New("map_shm() takes 4 arguments: size, protection, flags, name and offset.")));
+	}
+
+	const size_t size    = args[0]->ToInteger()->Value();
+	const v8::String::Utf8Value	name(args[3]->ToString());
+	const int fd = shm_open(*name, O_CREAT | O_RDWR | O_SYNC, 0666);
+  if (fd < 0)
+  {
+		return v8::ThrowException(node::ErrnoException(errno, "map_shm", ""));
+  }
+  ftruncate(fd, size);
+
+  v8::Handle<v8::Value> *mapArgs = (v8::Handle<v8::Value> *)calloc(sizeof(v8::Handle<v8::Value>), args.Length());
+  for (int i = 0; i < args.Length(); i++)
+		mapArgs[i] = args[i];
+  mapArgs[3] = v8::Integer::New(fd);
+
+  v8::Handle<v8::Object> global = v8::Context::GetCurrent()->Global();
+  v8::Handle<v8::Object> actualBuffer = map_symbol->Call(global, args.Length(), mapArgs)->ToObject();
+  free(mapArgs);
+  close(fd);
+
+	actualBuffer->ToObject()->Set(unlink_symbol, v8::FunctionTemplate::New(Unlink)->GetFunction());
+	actualBuffer->SetHiddenValue(name_symbol, v8::String::New(*name));
+
+	return scope.Close(actualBuffer);
+}
 
 static void RegisterModule(v8::Handle<v8::Object> target)
 {
@@ -120,8 +170,12 @@ static void RegisterModule(v8::Handle<v8::Object> target)
 	length_symbol = NODE_PSYMBOL("length");
 	sync_symbol   = NODE_PSYMBOL("sync");
 	unmap_symbol  = NODE_PSYMBOL("unmap");
+	unlink_symbol = NODE_PSYMBOL("unlink");
+	name_symbol = NODE_PSYMBOL("name");
 	buffer_symbol = NODE_PSYMBOL("Buffer");
 
+	map_symbol = v8::Persistent<v8::Function>::New(v8::FunctionTemplate::New(Map)->GetFunction());
+
 	const v8::PropertyAttribute attribs = (v8::PropertyAttribute) (v8::ReadOnly | v8::DontDelete);
 
 	target->Set(v8::String::New("PROT_READ"), v8::Integer::New(PROT_READ), attribs);
@@ -136,6 +190,7 @@ static void RegisterModule(v8::Handle<v8::Object> target)
 	target->Set(v8::String::New("MS_INVALIDATE"), v8::Integer::New(MS_INVALIDATE), attribs);
 
 	target->Set(v8::String::NewSymbol("map"),  v8::FunctionTemplate::New(Map)->GetFunction(), attribs);
+	target->Set(v8::String::NewSymbol("map_shm"),  v8::FunctionTemplate::New(MapShm)->GetFunction(), attribs);
 }
 
 NODE_MODULE(mmap, RegisterModule);

package.json

@@ -2,7 +2,7 @@
     "name": "mmap",
     "description": "mmap() fds into buffers",
     "license": "BSD",
-    "version": "2.0.2",
+    "version": "2.1.0",
     "main": "./index.js",
     "repository": { "type": "git", "url": "https://github.com/geocar/mmap.git" },
     "scripts": {