c - NodeJS / node-ffi: メモリリーク / 変数スコープ

Question

nodejs スクリプトのメモリ リークを調査しています。

次のコード ブロックを検討してください (ソース コード全体は一番下にあります)。GetImageバッファを割り当てる C 関数を呼び出し、それを解放するのは呼び出し元の責任です。行の後、GC中に解放されますかres.send(data)?var dataPtr

app.get('/test', function(req, res)
{
    res.contentType('image/jpeg');
    var lengthPtr = ref.alloc('uint');
    var dataPtr = ref.alloc('uchar*');
    lib.GetImage(dataPtr, lengthPtr);
    var length = lengthPtr.deref();
    var data = ref.reinterpret(ref.deref(dataPtr), length);
    res.send(data);
});

約 20000 件のリクエストを処理した後のエラー メッセージ:

Error: reinterpret: Cannot reinterpret from NULL pointer
    at Object.reinterpret (/home/ltse/LinuxPort/Experiments/NodeAddon/node_modules/ref/lib/ref.js:773:21)
    at Object.handle (/home/ltse/LinuxPort/Experiments/NodeAddon/ffi.js:20:17)
    at next_layer (/home/ltse/LinuxPort/Experiments/NodeAddon/node_modules/express/lib/router/route.js:103:13)
    at Route.dispatch (/home/ltse/LinuxPort/Experiments/NodeAddon/node_modules/express/lib/router/route.js:107:5)
    at /home/ltse/LinuxPort/Experiments/NodeAddon/node_modules/express/lib/router/index.js:213:24
    at Function.proto.process_params (/home/ltse/LinuxPort/Experiments/NodeAddon/node_modules/express/lib/router/index.js:284:12)
    at next (/home/ltse/LinuxPort/Experiments/NodeAddon/node_modules/express/lib/router/index.js:207:19)
    at Layer.expressInit [as handle] (/home/ltse/LinuxPort/Experiments/NodeAddon/node_modules/express/lib/middleware/init.js:23:5)
    at trim_prefix (/home/ltse/LinuxPort/Experiments/NodeAddon/node_modules/express/lib/router/index.js:255:15)
    at /home/ltse/LinuxPort/Experiments/NodeAddon/node_modules/express/lib/router/index.js:216:9

...same error message repeated many times...

Error: reinterpret: Cannot reinterpret from NULL pointer
    at Object.reinterpret (/home/ltse/LinuxPort/Experiments/NodeAddon/node_modules/ref/lib/ref.js:773:21)
    at Object.handle (/home/ltse/LinuxPort/Experiments/NodeAddon/ffi.js:20:17)
    at next_layer (/home/ltse/LinuxPort/Experiments/NodeAddon/node_modules/express/lib/router/route.js:103:13)
    at Route.dispatch (/home/ltse/LinuxPort/Experiments/NodeAddon/node_modules/express/lib/router/route.js:107:5)
    at /home/ltse/LinuxPort/Experiments/NodeAddon/node_modules/express/lib/router/index.js:213:24
    at Function.proto.process_params (/home/ltse/LinuxPort/Experiments/NodeAddon/node_modules/express/lib/router/index.js:284:12)
    at next (/home/ltse/LinuxPort/Experiments/NodeAddon/node_modules/express/lib/router/index.js:207:19)
    at Layer.expressInit [as handle] (/home/ltse/LinuxPort/Experiments/NodeAddon/node_modules/express/lib/middleware/init.js:23:5)
    at trim_prefix (/home/ltse/LinuxPort/Experiments/NodeAddon/node_modules/express/lib/router/index.js:255:15)
    at /home/ltse/LinuxPort/Experiments/NodeAddon/node_modules/express/lib/router/index.js:216:9
FATAL ERROR: Malloced operator new Allocation failed - process out of memory

NodeJS のソース コード:

var memwatch = require('memwatch');
var express = require('express');
var app = express();

var ref = require('ref');
var ffi = require('ffi');

var lib = ffi.Library('libsample', 
{
    'GetImage' : ['int', ['uchar **', 'uint *']]
});

app.get('/test', function(req, res)
{
    res.contentType('image/jpeg');
    var lengthPtr = ref.alloc('uint');
    var dataPtr = ref.alloc('uchar*');
    lib.GetImage(dataPtr, lengthPtr);
    var length = lengthPtr.deref();
    var data = ref.reinterpret(ref.deref(dataPtr), length);
    res.send(data);
});

var server = app.listen(3000, function(){
    console.log('Listening on port 3000.');
})

// memwatch
console.log('Monitoring memory usage...');
memwatch.on('leak', function(info){
    console.log(info);
});

memwatch.on('stats', function(info){
    console.log(info);
});

C 共有ライブラリのソース コード:

#include "sample.h"
#include <stdio.h>
#include <stdlib.h>

int GetImage(unsigned char** data, unsigned int * length)
{
    FILE *fp;
    unsigned int lSize;
    unsigned char *buffer;

    fp = fopen("***PATH TO JPG FILE***", "rb");
    fseek( fp , 0L , SEEK_END);
    lSize = ftell( fp );
    rewind( fp );

    buffer = calloc( 1, lSize+1 );

    fread( buffer, lSize, 1, fp);
    fclose(fp);

    *data = buffer;
    *length = lSize;

    return 0;
}

共有ライブラリを構築するコマンド:

gcc -g -c -Wall -Werror -fpic sample.c
gcc -shared -g -o libsample.so sample.o

Apache ベンチマーク ツールを使用して、プログラムをクラッシュさせました。

ab -n 120000 -c 4 http://localhost:3000/test