diff --git a/main/util/parallel.js b/main/util/parallel.js
index 627a883..d0d242a 100644
--- a/main/util/parallel.js
+++ b/main/util/parallel.js
@@ -249,72 +249,67 @@
     return this;
   };
 
-  Parallel.prototype._spawnMapWorker = function (i, cb, done, env, wrk) {
-    var that = this;
-
-    if (!wrk) wrk = that._spawnWorker(cb, env);
+  Parallel.prototype._initializeWorkerPool = function (size, cb, env) {
+    this.workerPool = [];
+    for (var i = 0; i < size; i++) {
+      var worker = this._spawnWorker(cb, env);
+      if (worker) {
+        this.workerPool.push(worker);
+      }
+    }
+  };
 
-    if (wrk !== undefined) {
-      wrk.onmessage = function (msg) {
-        that.data[i] = msg.data;
-        done(null, wrk);
-      };
-      wrk.onerror = function (e) {
-        wrk.terminate();
-        done(e);
-      };
-      wrk.postMessage(that.data[i]);
-    } else if (that.options.synchronous) {
-      setImmediate(function () {
-        that.data[i] = cb(that.data[i]);
-        done();
-      });
-    } else {
-      throw new Error(
-        "Workers do not exist and synchronous operation not allowed!"
-      );
+  Parallel.prototype._spawnMapWorker = function (i, cb, done, env) {
+    var that = this;
+  
+    if (!this.workerPool || this.workerPool.length === 0) {
+      throw new Error("Worker pool is not initialized or empty.");
     }
+  
+    var worker = this.workerPool.pop();
+    worker.onmessage = function (msg) {
+      that.data[i] = msg.data;
+      that.workerPool.push(worker); // Return worker to the pool
+      done(null);
+    };
+    worker.onerror = function (e) {
+      that.workerPool.push(worker); // Return worker to the pool even if there's an error
+      done(e);
+    };
+    worker.postMessage(that.data[i]);
   };
 
   Parallel.prototype.map = function (cb, env) {
     env = extend(this.options.env, env || {});
-
-    if (!this.data.length) {
-      return this.spawn(cb, env);
-    }
-
     var that = this;
     var startedOps = 0;
     var doneOps = 0;
-    function done(err, wrk) {
+  
+    if (!this.workerPool) {
+      this._initializeWorkerPool(this.options.maxWorkers, cb, env);
+    }
+  
+    var newOp = new Operation();
+    function done(err) {
       if (err) {
         newOp.resolve(err, null);
       } else if (++doneOps === that.data.length) {
         newOp.resolve(null, that.data);
-        if (wrk) wrk.terminate();
       } else if (startedOps < that.data.length) {
-        that._spawnMapWorker(startedOps++, cb, done, env, wrk);
-      } else {
-        if (wrk) wrk.terminate();
+        that._spawnMapWorker(startedOps++, cb, done, env);
       }
     }
-
-    var newOp = new Operation();
-    this.operation.then(
-      function () {
-        for (
-          ;
-          startedOps - doneOps < that.options.maxWorkers &&
-          startedOps < that.data.length;
-          ++startedOps
-        ) {
-          that._spawnMapWorker(startedOps, cb, done, env);
-        }
-      },
-      function (err) {
-        newOp.resolve(err, null);
+  
+    this.operation.then(function () {
+      for (
+        ;
+        startedOps - doneOps < that.options.maxWorkers &&
+        startedOps < that.data.length;
+        ++startedOps
+      ) {
+        that._spawnMapWorker(startedOps, cb, done, env);
       }
-    );
+    });
     this.operation = newOp;
     return this;
   };