JavaScript是一种单线程的编程语言。在使用Node.js的时候，如果有耗时的操作，需要放到异步函数中。Node.js的底层使用了libuv，用于实现异步I/O。

学习资源

• Node.js C/C++ Addons
• An Introduction to libuv
• Thread pool work scheduling
• .node-gyp\5.5.0\include\node\uv.h

优化Node.js条形码插件

安装

• Dynamsoft Barcode Reader
• Node.js
• node-gyp:

  npm install -g node-gyp

   

同步接口

先看下同步接口是怎么实现的。

创建dbr.cc，并在里面增加一个函数DecodeFile：

#include <node.h>
#include <node_buffer.h>
#include <string.h>
#include <uv.h>
#include "If_DBR.h"
#include "BarcodeFormat.h"
#include "BarcodeStructs.h"
#include "ErrorCode.h"using namespace v8;// Barcode format
const char * GetFormatStr(__int64 format)
{if (format == CODE_39)return "CODE_39";if (format == CODE_128)return "CODE_128";if (format == CODE_93)return "CODE_93";if (format == CODABAR)return "CODABAR";if (format == ITF)return "ITF";if (format == UPC_A)return "UPC_A";if (format == UPC_E)return "UPC_E";if (format == EAN_13)return "EAN_13";if (format == EAN_8)return "EAN_8";if (format == INDUSTRIAL_25)return "INDUSTRIAL_25";if (format == QR_CODE)return "QR_CODE";if (format == PDF417)return "PDF417";if (format == DATAMATRIX)return "DATAMATRIX";return "UNKNOWN";
}/**  decodeFile(fileName, barcodeTypes, callback)*/
void DecodeFile(const FunctionCallbackInfo<Value>& args) {Isolate* isolate = Isolate::GetCurrent();HandleScope scope(isolate);// get argumentsString::Utf8Value fileName(args[0]->ToString()); // convert v8 string to char *char *pFileName = *fileName; // file name__int64 llFormat = args[1]->IntegerValue();  // barcode typesLocal<Function> cb = Local<Function>::Cast(args[2]); // javascript callback function// initialize Dynamsoft Barcode Readerint iMaxCount = 0x7FFFFFFF;ReaderOptions ro = {0};pBarcodeResultArray pResults = NULL;ro.llBarcodeFormat = llFormat;ro.iMaxBarcodesNumPerPage = iMaxCount;// decode barcode imageint ret = DBR_DecodeFile(pFileName, &ro, &pResults);if (ret)printf("Detection error code: %d\n", ret);int count = pResults->iBarcodeCount;pBarcodeResult* ppBarcodes = pResults->ppBarcodes;pBarcodeResult tmp = NULL;// array for storing barcode resultsLocal<Array> barcodeResults = Array::New(isolate);for (int i = 0; i < count; i++){tmp = ppBarcodes[i];Local<Object> result = Object::New(isolate);result->Set(String::NewFromUtf8(isolate, "format"), String::NewFromUtf8(isolate, GetFormatStr(tmp->llFormat)));result->Set(String::NewFromUtf8(isolate, "value"), String::NewFromUtf8(isolate, tmp->pBarcodeData));barcodeResults->Set(Number::New(isolate, i), result);}// release memory of barcode resultsDBR_FreeBarcodeResults(&pResults);// run the callbackconst unsigned argc = 1;Local<Value> argv[argc] = { barcodeResults };cb->Call(isolate->GetCurrentContext()->Global(), argc, argv);
}void Init(Handle<Object> exports) {NODE_SET_METHOD(exports, "decodeFile", DecodeFile);
}NODE_MODULE(dbr, Init)

现在可以使用JavaScript接口decodeFile了。创建binding.gyp。针对Windows, Linux和macOS添加不同的头文件和库路径：

{"targets": [{'target_name': "dbr",'sources': [ "dbr.cc" ],'conditions': [['OS=="linux"', {'defines': ['LINUX_DBR',],'include_dirs': ["/home/xiao/Dynamsoft/BarcodeReader4.0/Include"],'libraries': ["-lDynamsoftBarcodeReaderx64", "-L/home/xiao/Dynamsoft/BarcodeReader4.0/Redist"],'copies': [{'destination': 'build/Release/','files': ['/home/xiao/Dynamsoft/BarcodeReader4.0/Redist/libDynamsoftBarcodeReaderx64.so']}]}],['OS=="win"', {'defines': ['WINDOWS_DBR',],'include_dirs': ["E:\Program Files (x86)\Dynamsoft\Barcode Reader 4.3\Components\C_C++\Include"],'libraries': ["-lE:\Program Files (x86)\Dynamsoft\Barcode Reader 4.3\Components\C_C++\Lib\DBRx64.lib"],'copies': [{'destination': 'build/Release/','files': ['E:\Program Files (x86)\Dynamsoft\Barcode Reader 4.3\Components\C_C++\Redist\DynamsoftBarcodeReaderx64.dll']}]}],['OS=="mac"', {'defines': ['MAC_DBR',],'include_dirs' : ["/Applications/Dynamsoft/Barcode\ Reader\ 4.1/Include"],'libraries': ["-lDynamsoftBarcodeReader"]}]]}]
}

配置构建环境：

node-gyp configure

编译工程：

node-gyp build

创建dbr.js测试下：

var dbr = require('./build/Release/dbr');
var readline = require('readline');
var fs = require('fs');
var barcodeTypes = 0x3FF | 0x2000000 | 0x8000000 | 0x4000000; // 1D, QRCODE, PDF417, DataMatrixfunction decodeFile(fileName) {dbr.decodeFile(fileName, barcodeTypes,function(msg) {var result = null;for (index in msg) {result = msg[index]console.log("Format: " + result['format']);console.log("Value : " + result['value']);console.log("##################");}});
}var rl = readline.createInterface({input: process.stdin,output: process.stdout
});rl.question("Please input a barcode image path: ", function(answer) {decodeFile(answer);rl.close();
});

异步接口

虽然这样封装接口也是通过回调函数返回的，但是所有的工作都在主线程中，会造成堵塞。解决的方法就是把耗时的工作放到工作线程中。使用接口uv_queue_work(uv_loop_t* loop, uv_work_t* req, uv_work_cb work_cb, uv_after_work_cb after_work_cb)可以把任务放到libuv的线程池中。

新建接口decodeFileAsync：

/**  decodeFileAsync(fileName, barcodeTypes, callback)*/
void DecodeFileAsync(const FunctionCallbackInfo<Value>& args) {Isolate* isolate = Isolate::GetCurrent();HandleScope scope(isolate);// get argumentsString::Utf8Value fileName(args[0]->ToString()); // file namechar *pFileName = *fileName;__int64 llFormat = args[1]->IntegerValue(); // barcode typesLocal<Function> cb = Local<Function>::Cast(args[2]); // javascript callback function// initialize BarcodeWorkerBarcodeWorker *worker = new BarcodeWorker;worker->request.data = worker;strcpy(worker->filename, pFileName);worker->callback.Reset(isolate, cb);worker->llFormat = llFormat;worker->pResults = NULL;worker->buffer = NULL;uv_queue_work(uv_default_loop(), &worker->request, (uv_work_cb)DetectionWorking, (uv_after_work_cb)DetectionDone);
}void Init(Handle<Object> exports) {NODE_SET_METHOD(exports, "decodeFile", DecodeFile);NODE_SET_METHOD(exports, "decodeFileAsync", DecodeFileAsync);
}

把条形码的解码识别工作放到uv_work_cb回调函数中：

/**  uv_work_cb*/
static void DetectionWorking(uv_work_t *req)
{// get the reference to BarcodeWorkerBarcodeWorker *worker = static_cast<BarcodeWorker *>(req->data);// initialize Dynamsoft Barcode Readerint iMaxCount = 0x7FFFFFFF;ReaderOptions ro = {0};pBarcodeResultArray pResults = NULL;ro.llBarcodeFormat = worker->llFormat;ro.iMaxBarcodesNumPerPage = iMaxCount;// decode barcode imageint ret = 0;if (worker->buffer) {ret = DBR_DecodeStream(worker->buffer, worker->size, &ro, &pResults);}else{ret = DBR_DecodeFile(worker->filename, &ro, &pResults);}if (ret)printf("Detection error code: %d\n", ret);// save results to BarcodeWorkerworker->errorCode = ret;worker->pResults = pResults;
}

uv_after_work_cb回调函数用来在主线程显示结果：

/**  uv_after_work_cb*/
static void DetectionDone(uv_work_t *req,int status)
{Isolate* isolate = Isolate::GetCurrent();HandleScope scope(isolate);// get the reference to BarcodeWorkerBarcodeWorker *worker = static_cast<BarcodeWorker *>(req->data);// get barcode resultspBarcodeResultArray pResults = worker->pResults;int errorCode = worker->errorCode;int count = pResults->iBarcodeCount;pBarcodeResult* ppBarcodes = pResults->ppBarcodes;pBarcodeResult tmp = NULL;// array for storing barcode resultsLocal<Array> barcodeResults = Array::New(isolate);for (int i = 0; i < count; i++){tmp = ppBarcodes[i];Local<Object> result = Object::New(isolate);result->Set(String::NewFromUtf8(isolate, "format"), String::NewFromUtf8(isolate, GetFormatStr(tmp->llFormat)));result->Set(String::NewFromUtf8(isolate, "value"), String::NewFromUtf8(isolate, tmp->pBarcodeData));barcodeResults->Set(Number::New(isolate, i), result);}// release memory of barcode resultsDBR_FreeBarcodeResults(&pResults);// run the callbackconst unsigned argc = 1;Local<Value> argv[argc] = {barcodeResults};Local<Function> cb = Local<Function>::New(isolate, worker->callback);cb->Call(isolate->GetCurrentContext()->Global(), argc, argv);// release memory of BarcodeWorkerdelete worker;
}

修改dbr.js调用异步接口：

var dbr = require('./build/Release/dbr');
var readline = require('readline');
var fs = require('fs');
var barcodeTypes = 0x3FF | 0x2000000 | 0x8000000 | 0x4000000; // 1D, QRCODE, PDF417, DataMatrixfunction decodeFileAsync(fileName) {dbr.decodeFileAsync(fileName, barcodeTypes,function(msg) {var result = null;for (index in msg) {result = msg[index]console.log("Format: " + result['format']);console.log("Value : " + result['value']);console.log("##################");}});
}var rl = readline.createInterface({input: process.stdin,output: process.stdout
});rl.question("Please input a barcode image path: ", function(answer) {decodeFileAsync(answer);rl.close();
});

源码

https://github.com/yushulx/nodejs-barcode-for-win-linux-mac