Soot Concurrent Modification Bug Fix (#19)

* Added semaphore to prevent concurrent modification when  loading soot clases

* Formatted code

build.sbt

@@ -6,7 +6,7 @@ scalaVersion := "2.13.6"
 val cpgVersion       = "1.3.392"
 val sootVersion      = "4.2.1"
 val slf4jVersion     = "1.7.32"
-val scalatestVersion = "3.1.1"
+val scalatestVersion = "3.2.9"
 
 Test / fork := true
 resolvers ++= Seq(

src/main/scala/io/joern/jimple2cpg/passes/AstCreationPass.scala

@@ -6,11 +6,12 @@ import org.slf4j.LoggerFactory
 import soot.{Scene, SootClass}
 
 import java.io.{File => JFile}
-import java.util.concurrent.ConcurrentHashMap
+import java.util.concurrent.{ConcurrentHashMap, Semaphore}
 import scala.tools.nsc
 
 case class Global(
-    usedTypes: ConcurrentHashMap[String, Boolean] = new ConcurrentHashMap[String, Boolean]()
+    usedTypes: ConcurrentHashMap[String, Boolean] = new ConcurrentHashMap[String, Boolean](),
+    sootLock: Semaphore = new Semaphore(1)
 )
 
 class AstCreationPass(codePath: String, filenames: List[String], cpg: Cpg, keyPool: IntervalKeyPool)
@@ -33,7 +34,12 @@ class AstCreationPass(codePath: String, filenames: List[String], cpg: Cpg, keyPo
     val qualifiedClassName           = getQualifiedClassPath(filename)
     var sootClass: Option[SootClass] = None
     try {
-      sootClass = Option(Scene.v().loadClassAndSupport(qualifiedClassName))
+      try {
+        global.sootLock.acquire()
+        sootClass = Option(Scene.v().loadClassAndSupport(qualifiedClassName))
+      } finally {
+        global.sootLock.release()
+      }
       sootClass match {
         case Some(clazz) => new AstCreator(filename, global).createAst(clazz)
         case None        => null