Interprocess shared memory cache for Node.JS

It supports auto memory-management and fast object serialization. It uses a hashmap and LRU cache internally to maintain its contents.

This software (source code and its binary builds) is absolutely copy free and any download or modification is permitted except for unprohibited commercial use.

But due to the complexity of this software, any bugs or runtime exceptions could happen when programs which includeed it run into an unexpected situation, which in most cases should be harmless but also have the chance to cause:

• program crash
• system down
• software damage
• hardware damage

which would lead to data corruption or even economic losses.

So when you are using this software, DO

• check the data
• double check the data
• avoid undefined behavior to happen

To avoid data crupption, we use a read-write lock to ensure that data modification is exclusive. But when a program is writting data when something bad, for example, a SIGKILL, happens that crashes the program before the write operation is complete and lock is released, other processes may not be able to enter the exclusive region again. I do not use an auto recovery lock such as flock, which will automatically release when process exits, just in case that wrong data is returned when performing a reading operation, or even, causing a segment fault.

var cache = require('node-shared-cache');
var obj = new cache.Cache("test", 557056);
// setting property
obj.foo = "bar";
// getting property
console.log(obj.foo);
// enumerating properties
for(var k in obj);
Object.keys(obj);
// deleting property
delete obj.foo;
// writing objects is also supported
obj.foo = {'foo': 'bar'};
// but original object reference is not saved
var test = obj.foo = {'foo': 'bar'};
test === obj.foo; // false
// circular reference is supported.
test.self = test;
obj.foo = test;
// and saved result is also circular
test = obj.foo;
test.self === test; // true

function Cache(name, size)

name represents a file name in shared memory, size represents memory size in bytes to be used. Note that:

• size should not be smaller than 557056 (544KB)
• size should not be larger than 2147483647 (2GB)
• size is 32KB aligned

set(name, value)

Note that:

• the length of name should not be longer than 256 characters (limited by internal design)

Tests are run under a virtual machine with one processor:

$ node -v
v0.12.4
$ cat /proc/cpuinfo
processor   : 0
vendor_id   : GenuineIntel
cpu family  : 6
model       : 45
model name  : Intel(R) Xeon(R) CPU E5-2630 0 @ 2.30GHz
stepping    : 7
microcode   : 0x70d
cpu MHz     : 2300.090
cache size  : 15360 KB    
...

When setting property 100w times:

// test plain object
var plain = {};
console.time('plain obj');
for(var i = 0; i < 1000000; i++) {
    plain['test' + (i & 127)] = i;
}
console.timeEnd('plain obj');

// test shared cache
var obj = new binding.Cache("test", 1048576);
console.time('shared cache');
for(var i = 0; i < 1000000; i++) {
    obj['test' + (i & 127)] = i;
}
console.timeEnd('shared cache');

The result is:

plain obj: 229ms
shared cache: 588ms

When trying to read existing key:

console.time('read plain obj');
for(var i = 0; i < 1000000; i++) {
    plain['test' + (i & 127)];
}
console.timeEnd('read plain obj');

console.time('read shared cache');
for(var i = 0; i < 1000000; i++) {
    obj['test' + (i & 127)];
}
console.timeEnd('read shared cache');

The result is:

read plain obj: 135ms
read shared cache: 639ms

When trying to read keys that are not existed:

console.time('read plain obj with key absent');
for(var i = 0; i < 1000000; i++) {
    plain['oops' + (i & 127)];
}
console.timeEnd('read plain obj with key absent');

console.time('read shared cache with key absent');
for(var i = 0; i < 1000000; i++) {
    obj['oops' + (i & 127)];
}
console.timeEnd('read shared cache with key absent');

The result is:

read plain obj with key absent: 254ms
read shared cache with key absent: 538ms

When enumerating all the keys:

console.time('enumerate plain obj');
for(var i = 0; i < 100000; i++) {
    Object.keys(plain);
}
console.timeEnd('enumerate plain obj');

console.time('enumerate shared cache');
for(var i = 0; i < 100000; i++) {
    Object.keys(obj);
}
console.timeEnd('enumerate shared cache');

The result is:

enumerate plain obj: 1218ms
enumerate shared cache: 4294ms

Warn: Because the shared memory can be modified at any time even the current Node.js process is running, depending on keys enumeration result to determine whether a key is cached is unwise. On the other hand, it takes so long a time to build strings from memory slice, as well as putting them into an array, so DO NOT USE IT unless you know that what you are doing.

We choose a c-style binary serialization method rather than JSON.stringify, in two concepts:

• Performance serializing and unserializing
• Support for circular reference

Tests code list:

var input = {env: process.env, arr: [process.env, process.env]};
console.time('JSON.stringify');
for(var i = 0; i < 100000; i++) {
    JSON.stringify(input);
}
console.timeEnd('JSON.stringify');

console.time('binary serialization');
for(var i = 0; i < 100000; i++) {
    obj.test = input;
}
console.timeEnd('binary serialization');

// test object unserialization
input = JSON.stringify(input);
console.time('JSON.parse');
for(var i = 0; i < 100000; i++) {
    JSON.parse(input);
}
console.timeEnd('JSON.parse');

console.time('binary unserialization');
for(var i = 0; i < 100000; i++) {
    obj.test;
}
console.timeEnd('binary unserialization');

The result is:

JSON.stringify: 6183ms
binary serialization: 2633ms
JSON.parse: 2083ms
binary unserialization: 2225ms

• add dead-lock auto recovery when data is inconsistent