force cache delete option

add the possibility to force delete the cache dir ignoring any possible
problems this can cause.

Author: mawinter69

src/main/java/org/jenkinsci/plugins/workflow/libs/LibraryCachingConfiguration.java

@@ -17,10 +17,16 @@
 import java.util.List;
 import java.util.concurrent.TimeUnit;
 import java.util.concurrent.locks.ReentrantReadWriteLock;
+import java.util.logging.Level;
+import java.util.logging.Logger;
+
 import org.apache.commons.io.IOUtils;
 import org.apache.commons.lang.StringUtils;
 
 public final class LibraryCachingConfiguration extends AbstractDescribableImpl<LibraryCachingConfiguration> {
+    
+    private static final Logger LOGGER = Logger.getLogger(LibraryCachingConfiguration.class.getName());
+    
     private int refreshTimeMinutes;
     private String excludedVersionsStr;
 
@@ -83,7 +89,7 @@ public static FilePath getGlobalLibrariesCacheDir() {
     }
 
     @Extension public static class DescriptorImpl extends Descriptor<LibraryCachingConfiguration> {
-        public FormValidation doClearCache(@QueryParameter String name) throws InterruptedException {
+        public FormValidation doClearCache(@QueryParameter String name, @QueryParameter boolean forceDelete) throws InterruptedException {
             Jenkins.get().checkPermission(Jenkins.ADMINISTER);
 
             try {
@@ -94,19 +100,26 @@ public FormValidation doClearCache(@QueryParameter String name) throws Interrupt
                         try (InputStream stream = libraryNamePath.read()) {
                             cacheName = IOUtils.toString(stream, StandardCharsets.UTF_8);
                         }
-                        if (libraryNamePath.readToString().equals(name)) {
+                        if (cacheName.equals(name)) {
                             FilePath libraryCachePath = LibraryCachingConfiguration.getGlobalLibrariesCacheDir()
                                     .child(libraryNamePath.getName().replace("-name.txt", ""));
-                            ReentrantReadWriteLock retrieveLock = LibraryAdder.getReadWriteLockFor(libraryCachePath.getName());
-                            if (retrieveLock.writeLock().tryLock(10, TimeUnit.SECONDS)) {
-                                try {
-                                    libraryCachePath.deleteRecursive();
-                                    libraryNamePath.delete();
-                                } finally {
-                                    retrieveLock.writeLock().unlock();
-                                }
+                            if (forceDelete) {
+                                LOGGER.log(Level.FINER, "Force deleting cache for {0}", name);
+                                libraryCachePath.deleteRecursive();
+                                libraryNamePath.delete();
                             } else {
-                                return FormValidation.error("The cache dir is currently used by another thread, so deletion was not possibly. Please try again");
+                                LOGGER.log(Level.FINER, "Safe deleting cache for {0}", name);
+                                ReentrantReadWriteLock retrieveLock = LibraryAdder.getReadWriteLockFor(libraryCachePath.getName());
+                                if (retrieveLock.writeLock().tryLock(10, TimeUnit.SECONDS)) {
+                                    try {
+                                        libraryCachePath.deleteRecursive();
+                                        libraryNamePath.delete();
+                                    } finally {
+                                        retrieveLock.writeLock().unlock();
+                                    }
+                                } else {
+                                    return FormValidation.error("The cache dir could not be deleted because it is currently being used by another thread. Please try again.");
+                                }
                             }
                         }
                     }

src/main/resources/org/jenkinsci/plugins/workflow/libs/LibraryCachingConfiguration/config.jelly

@@ -32,6 +32,9 @@ THE SOFTWARE.
         <f:textbox />
     </f:entry>
     <j:if test="${h.hasPermission(app.ADMINISTER)}">
-        <f:validateButton title="${%Clear cache}" progress="${%Clearing...}" method="clearCache" with="name" />
+        <f:entry title="${%Force clear cache}" field="forceDelete">
+          <f:checkbox/>
+        </f:entry>
+        <f:validateButton title="${%Clear cache}" progress="${%Clearing...}" method="clearCache" with="name,forceDelete" />
     </j:if>
 </j:jelly>

src/main/resources/org/jenkinsci/plugins/workflow/libs/LibraryCachingConfiguration/help-forceDelete.html

@@ -0,0 +1,6 @@
+<div>
+    To avoid that clearing the cache interferes with running builds this process is normally guarded by locks.
+    Pressing the <i>Clear Cache</i> button will wait for a maximum of 10 seconds to get a lock.<br/>
+    By checking this option, the library will be deleted immediately without acquiring a lock. This can lead to build errors 
+    if a build is copying the library from the cache while it gets delete. This risk is all the greater, the larger the library is.
+</div>

src/test/java/org/jenkinsci/plugins/workflow/libs/LibraryCachingConfigurationTest.java

@@ -177,7 +177,7 @@ public void clearCache() throws Exception {
         assertThat(new File(cache.getRemote()), anExistingDirectory());
         assertThat(new File(cache.withSuffix("-name.txt").getRemote()), anExistingFile());
         // Clear the cache. TODO: Would be more realistic to set up security and use WebClient.
-        ExtensionList.lookupSingleton(LibraryCachingConfiguration.DescriptorImpl.class).doClearCache("library");
+        ExtensionList.lookupSingleton(LibraryCachingConfiguration.DescriptorImpl.class).doClearCache("library", false);
         assertThat(new File(cache.getRemote()), not(anExistingDirectory()));
         assertThat(new File(cache.withSuffix("-name.txt").getRemote()), not(anExistingFile()));
     }