v0.4.34: purge() cancels in-flight download (per-URL cancellation)

videoCache remove(=purge) 가 다운로드 중인 항목도 취소하도록 per-URL 세대
(DOWNLOAD_GEN) 채널 추가. 기존엔 READY/디스크 최종 파일만 지워서, 느린/큰
영상이 다운로드 중에 evict 되면 완료 후 다시 디스크+READY 에 되살아남.
이제 purge 가 세대를 제거 → download 의 cancelled() 검사(읽기 루프 + 모든
publish 지점)가 실패 → .part/승격 파일 self-clean. clearAll/wipe/clearIndex
도 DOWNLOAD_GEN 정리. 데이터팩 keep(FIFO) 메모리 관리 보장에 필요.

Co-Authored-By: Claude Opus 4 <noreply@anthropic.com>

gradle.properties

@@ -5,7 +5,7 @@ org.gradle.configuration-cache=false
 
 # Mod
 mod_id=video_player
-mod_version=0.4.33
+mod_version=0.4.34
 maven_group=com.ejclaw.videoplayer
 archives_base_name=video_player
 

src/main/java/com/ejclaw/videoplayer/client/playback/VideoCache.java

@@ -52,6 +52,18 @@ public final class VideoCache {
      */
     private static final AtomicLong CACHE_EPOCH = new AtomicLong(0);
 
+    /**
+     * Per-URL cancellation channel for {@link #purge(String)}. The global {@link #CACHE_EPOCH}
+     * can only cancel <em>all</em> in-flight downloads at once; a targeted purge needs to stop
+     * exactly one. Each submitted download captures a unique generation here at submit time;
+     * {@link #purge(String)} removes the URL's entry, which makes the running download's
+     * {@link #cancelled(String, long, long)} checks (read loop + every publish point) fail and
+     * self-clean its {@code .part}/promoted file instead of re-publishing post-purge.
+     */
+    private static final Map<String, Long> DOWNLOAD_GEN = new ConcurrentHashMap<>();
+    /** Monotonic source for per-download generations stored in {@link #DOWNLOAD_GEN}. */
+    private static final AtomicLong GEN_SEQ = new AtomicLong(0);
+
     /**
      * Single-thread executor that serializes all downloads. Cap enforcement (the total
      * cache size check) needs an authoritative view of the cache directory at the moment a
@@ -103,6 +115,12 @@ public final class VideoCache {
     /** Server-driven delete of a cached URL. Removes from READY and from disk. */
     public static void purge(String url) {
         if (url == null || url.isEmpty()) return;
+        // Cancel any in-flight download of this exact URL first. Dropping its generation
+        // makes the download thread's cancelled() checks fail, so it deletes its own .part
+        // (or rolls back a just-promoted file) instead of finishing and re-publishing after
+        // we've purged. Without this, a slow/large download evicted mid-flight would silently
+        // reappear on disk + in READY once it completed.
+        DOWNLOAD_GEN.remove(url);
         Path p = READY.remove(url);
         if (p == null) {
             // Not in this session's index, but the file may still be on disk from a prior run.
@@ -158,6 +176,7 @@ public final class VideoCache {
         // Phase 2: drop indexes.
         READY.clear();
         IN_FLIGHT.clear();
+        DOWNLOAD_GEN.clear();
 
         // Phase 3: delete files on disk.
         int deleted = 0;
@@ -209,7 +228,11 @@ public final class VideoCache {
         // CACHE_EPOCH later — any mismatch means clearAll() ran in between and this
         // download must abort without publishing.
         long epoch = CACHE_EPOCH.get();
-        DOWNLOAD_POOL.submit(() -> download(url, epoch));
+        // Register a unique generation for this download so a targeted purge() can cancel
+        // exactly this URL (see DOWNLOAD_GEN / cancelled()).
+        long gen = GEN_SEQ.incrementAndGet();
+        DOWNLOAD_GEN.put(url, gen);
+        DOWNLOAD_POOL.submit(() -> download(url, epoch, gen));
     }
 
     /** Return the local cached file path for this URL, or {@code null} if not yet ready. */
@@ -224,6 +247,7 @@ public final class VideoCache {
     public static void clearIndex() {
         READY.clear();
         IN_FLIGHT.clear();
+        DOWNLOAD_GEN.clear();
     }
 
     /**
@@ -237,6 +261,7 @@ public final class VideoCache {
         CACHE_EPOCH.incrementAndGet();
         READY.clear();
         IN_FLIGHT.clear();
+        DOWNLOAD_GEN.clear();
         int deleted = 0;
         int failed  = 0;
         try {
@@ -283,16 +308,16 @@ public final class VideoCache {
      * @return {@code true} if the entry is now published; {@code false} if the
      *         caller's work was cancelled and {@code path} has been cleaned up.
      */
-    private static boolean publishIfNotCancelled(String url, Path path, long startEpoch) {
-        // If the wipe ran between download's pre-move epoch check and Files.move, its
-        // directory scan won't have seen this just-promoted file. We must delete it here,
-        // not just bail — otherwise the freshly-moved final file leaks across shutdown.
-        if (CACHE_EPOCH.get() != startEpoch) {
+    private static boolean publishIfNotCancelled(String url, Path path, long startEpoch, long startGen) {
+        // If a wipe (clearAll) or a targeted purge ran between download's pre-move check and
+        // Files.move, its directory scan won't have seen this just-promoted file. We must
+        // delete it here, not just bail — otherwise the freshly-moved final file leaks.
+        if (cancelled(url, startEpoch, startGen)) {
             try { Files.deleteIfExists(path); } catch (Throwable ignored) {}
             return false;
         }
         READY.put(url, path);
-        if (CACHE_EPOCH.get() != startEpoch) {
+        if (cancelled(url, startEpoch, startGen)) {
             READY.remove(url, path);
             try { Files.deleteIfExists(path); } catch (Throwable ignored) {}
             return false;
@@ -300,7 +325,19 @@ public final class VideoCache {
         return true;
     }
 
-    private static void download(String url, long startEpoch) {
+    /**
+     * True if the in-flight download for {@code url} should abort and self-clean. Two channels:
+     * a global wipe ({@link #clearAll()}/{@link #wipeOnShutdown()} bumped {@link #CACHE_EPOCH}),
+     * or a targeted {@link #purge(String)} that removed/replaced this URL's generation in
+     * {@link #DOWNLOAD_GEN}.
+     */
+    private static boolean cancelled(String url, long startEpoch, long startGen) {
+        if (CACHE_EPOCH.get() != startEpoch) return true;
+        Long cur = DOWNLOAD_GEN.get(url);
+        return cur == null || cur.longValue() != startGen;
+    }
+
+    private static void download(String url, long startEpoch, long startGen) {
         Path cacheDir = cacheDir();
         Path partPath = null;
         try {
@@ -311,8 +348,8 @@ public final class VideoCache {
             }
             // Pre-flight cancellation check — if clearAll already ran between submit and now,
             // skip the whole thing. Avoids creating directories / .part files post-clear.
-            if (CACHE_EPOCH.get() != startEpoch) {
-                VideoPlayerMod.LOG.info("[{}] preload: cancelled before start (clearAll ran) — {}",
+            if (cancelled(url, startEpoch, startGen)) {
+                VideoPlayerMod.LOG.info("[{}] preload: cancelled before start (clearAll/purge ran) — {}",
                     VideoPlayerMod.MOD_ID, url);
                 return;
             }
@@ -326,8 +363,8 @@ public final class VideoCache {
             // Resume-friendly: if the file's already on disk from an earlier session, just
             // index it without re-downloading.
             if (Files.exists(finalPath) && Files.size(finalPath) > 0) {
-                if (!publishIfNotCancelled(url, finalPath, startEpoch)) {
-                    VideoPlayerMod.LOG.info("[{}] preload: reindex cancelled (clearAll ran) — {}",
+                if (!publishIfNotCancelled(url, finalPath, startEpoch, startGen)) {
+                    VideoPlayerMod.LOG.info("[{}] preload: reindex cancelled (clearAll/purge ran) — {}",
                         VideoPlayerMod.MOD_ID, url);
                     return;
                 }
@@ -378,7 +415,7 @@ public final class VideoCache {
                     // Cancellation check inside the loop. Break (not return) so the try-with
                     // closes the output stream first — on Windows, deleting an open .part can
                     // fail with AccessDeniedException, so we always close before deleting.
-                    if (CACHE_EPOCH.get() != startEpoch) {
+                    if (cancelled(url, startEpoch, startGen)) {
                         cancelled = true;
                         break;
                     }
@@ -416,8 +453,8 @@ public final class VideoCache {
 
             // Pre-move cancellation check. If clearAll ran during the read loop, abort
             // before promoting .part to final — saves a wasted move + delete.
-            if (CACHE_EPOCH.get() != startEpoch) {
-                VideoPlayerMod.LOG.info("[{}] preload: cancelled before move (clearAll ran) — {}",
+            if (cancelled(url, startEpoch, startGen)) {
+                VideoPlayerMod.LOG.info("[{}] preload: cancelled before move (clearAll/purge ran) — {}",
                     VideoPlayerMod.MOD_ID, url);
                 try { Files.deleteIfExists(partPath); } catch (Throwable ignored) {}
                 return;
@@ -431,8 +468,8 @@ public final class VideoCache {
             // the window between READY.put and the "완료" notification (clearAll wipes
             // READY then we re-publish + emit stale completion chat). publishIfNotCancelled
             // rolls back both READY and the on-disk file if the epoch moved at any time.
-            if (!publishIfNotCancelled(url, finalPath, startEpoch)) {
-                VideoPlayerMod.LOG.info("[{}] preload: cancelled at publish (clearAll ran) — {}",
+            if (!publishIfNotCancelled(url, finalPath, startEpoch, startGen)) {
+                VideoPlayerMod.LOG.info("[{}] preload: cancelled at publish (clearAll/purge ran) — {}",
                     VideoPlayerMod.MOD_ID, url);
                 return;
             }
@@ -451,6 +488,9 @@ public final class VideoCache {
             }
         } finally {
             IN_FLIGHT.remove(url);
+            // Only clear our own generation — a re-preload after a purge may have installed a
+            // newer gen for this URL that must survive.
+            DOWNLOAD_GEN.remove(url, startGen);
         }
     }