DEF-3522 Fixed race condition when downloading sdk's (#102)

server/src/main/java/com/defold/extender/services/DefoldSdkService.java

@@ -5,6 +5,7 @@
 import org.apache.commons.io.FileUtils;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
+import org.apache.commons.io.FileUtils;
 import org.springframework.beans.factory.annotation.Autowired;
 import org.springframework.beans.factory.annotation.Value;
 import org.springframework.boot.actuate.metrics.CounterService;
@@ -25,6 +26,7 @@
 import java.net.URL;
 import java.nio.file.Files;
 import java.nio.file.Path;
+import java.nio.file.StandardCopyOption;
 import java.util.Comparator;
 
 @Service
@@ -52,6 +54,24 @@ public class DefoldSdkService {
         this.dynamoHome = System.getenv("DYNAMO_HOME") != null ? new File(System.getenv("DYNAMO_HOME")) : null;
     }
 
+    // Helper function to move the SDK directories
+    public static void Move(Path source, Path target) {
+        try {
+            Files.move(source, target, StandardCopyOption.ATOMIC_MOVE);
+        } catch (IOException e) {
+            // If the target path suddenly exists, and the source path still exists,
+            // then we failed with the atomic move, and we assume another job succeeded with the download
+            if (Files.exists(source) && Files.exists(target)) {
+                LOGGER.info("Defold SDK version {} was downloaded by another job in the meantime", source.toString());
+                try {
+                    FileUtils.deleteDirectory(source.toFile());
+                } catch (IOException e2) {
+                    LOGGER.error("Failed to delete temp sdk directory {}: {}", source.toString(), e2.getMessage());
+                }
+            }
+        }
+    }
+
     public File getSdk(String hash) throws IOException, URISyntaxException, ExtenderException {
         long methodStart = System.currentTimeMillis();
 
@@ -72,9 +92,13 @@ public File getSdk(String hash) throws IOException, URISyntaxException, Extender
                     throw new ExtenderException(String.format("The given sdk does not exist: %s (%s)", hash, response.getStatusCode().toString()));
                 }
 
-                Files.createDirectories(sdkDirectory.toPath());
+                File tmpSdkDirectory = Files.createTempDirectory(baseSdkDirectory, hash).toFile(); // Either moved or deleted later by Move()
+
+                Files.createDirectories(tmpSdkDirectory.toPath());
                 InputStream body = response.getBody();
-                ZipUtils.unzip(body, sdkDirectory.toPath());
+                ZipUtils.unzip(body, tmpSdkDirectory.toPath());
+
+                Move(tmpSdkDirectory.toPath(), sdkDirectory.toPath());
             }
 
             // Delete old SDK:s