Meteor methods blocking even with this.unblock(). Have I hit a limit in concurrent Fibers?

Question

this is my code: server.js

var fs = Npm.require('fs');
Meteor.methods({
    "test":function(a){
      this.unblock();
      if(a==1){
         //NVIDIA is a test file and size is 40 M ,
         //Make the call spend more time to watch block happen
          var data = fs.readFileSync("/home/ec/download/NVIDIA");
          for(var i=0;i<5;i++){
            fs.writeFileSync("/home/ec/download/test/NVIDIA"+i, data);
          }
      }
      console.log(a);   
      return a;
    }
});

client.js

Meteor.call("test",1);
Meteor.call("test",2);

the result is :

1
2

the second call is blocked and the new Fibers is not created. Any idea about this ? thanks!

Answer 1

I think this is happening because you are using fs.writeFileSync, which is blocking on a lower level than Fibers has access to.

Node waits on a blocking File IO operation which is still blocking with fibers unless you use it asynchronously.

If you use the callback style writeFile instead:

var readFile = Meteor._wrapAsync(fs.readFile.bind(fs));
var writeFile = Meteor._wrapAsync(fs.writeFile.bind(fs));

var data = readFile("/home/ec/download/NVIDIA");

for(var i=0;i<5;i++){
    writeFile("/home/ec/download/test/NVIDIA"+i, data);
}

Then this would bring up the writeFile and readFile methods up to the event loop where fibers has access to it.

Hopefully this should give you the behavior you expect.