From 7b8db2e221ff94206ee0b75003045e57171ba4c9 Mon Sep 17 00:00:00 2001
From: Gary O'Neall <gary@sourceauditor.com>
Date: Mon, 11 Mar 2024 14:36:52 -0700
Subject: [PATCH] Make the Mojo threadsafe

Fixes #161

Signed-off-by: Gary O'Neall <gary@sourceauditor.com>
---
 .../java/org/spdx/maven/CreateSpdxMojo.java     |  4 ++--
 .../maven/utils/MavenToSpdxLicenseMapper.java   | 17 +++++++++++++----
 2 files changed, 15 insertions(+), 6 deletions(-)

diff --git a/src/main/java/org/spdx/maven/CreateSpdxMojo.java b/src/main/java/org/spdx/maven/CreateSpdxMojo.java
index 7b5bde3..afda541 100644
--- a/src/main/java/org/spdx/maven/CreateSpdxMojo.java
+++ b/src/main/java/org/spdx/maven/CreateSpdxMojo.java
@@ -28,7 +28,6 @@
 import org.apache.maven.plugins.annotations.LifecyclePhase;
 import org.apache.maven.plugins.annotations.Mojo;
 import org.apache.maven.plugins.annotations.Parameter;
-import org.apache.maven.plugins.annotations.ResolutionScope;
 import org.apache.maven.project.DefaultProjectBuildingRequest;
 import org.apache.maven.project.MavenProject;
 import org.apache.maven.project.MavenProjectHelper;
@@ -98,7 +97,8 @@
  */
 @Mojo( name = "createSPDX",
        defaultPhase = LifecyclePhase.VERIFY,
-        requiresOnline = true )
+        requiresOnline = true,
+       threadSafe = true )
 public class CreateSpdxMojo extends AbstractMojo
 {
     public static final String INCLUDE_ALL = "**/*";
diff --git a/src/main/java/org/spdx/maven/utils/MavenToSpdxLicenseMapper.java b/src/main/java/org/spdx/maven/utils/MavenToSpdxLicenseMapper.java
index 391c90d..6847044 100644
--- a/src/main/java/org/spdx/maven/utils/MavenToSpdxLicenseMapper.java
+++ b/src/main/java/org/spdx/maven/utils/MavenToSpdxLicenseMapper.java
@@ -61,7 +61,8 @@ public class MavenToSpdxLicenseMapper
     private static final String LISTED_LICENSE_JSON_URL = SPDX_LICENSE_URL_PREFIX + "licenses.json";
     private static final String LISTED_LICENSE_JSON_PATH = "resources/licenses.json";
 
-    static MavenToSpdxLicenseMapper instance;
+    static volatile MavenToSpdxLicenseMapper instance;
+    private static Object instanceMutex = new Object();
     private Map<String, String> urlStringToSpdxLicenseId;
 
     private MavenToSpdxLicenseMapper() throws LicenseMapperException
@@ -101,11 +102,19 @@ private MavenToSpdxLicenseMapper() throws LicenseMapperException
 
     public static MavenToSpdxLicenseMapper getInstance() throws LicenseMapperException
     {
-        if ( instance == null )
+        MavenToSpdxLicenseMapper result = instance;
+        if ( result == null )
         {
-            instance = new MavenToSpdxLicenseMapper();
+            synchronized ( instanceMutex )
+            {
+                result = instance;
+                if ( result == null )
+                {
+                    instance = result = new MavenToSpdxLicenseMapper();
+                }
+            }
         }
-        return instance;
+        return result;
     }
 
     /**