fix: high concurrency issue with 503 context closure

src/core/BrowserManager.js

@@ -55,6 +55,9 @@ class BrowserManager {
 
         // ConnectionRegistry reference (set after construction to avoid circular dependency)
         this.connectionRegistry = null;
+        this._onAuthQueuesDrained = null;
+        this._isSystemBusyProvider = null;
+        this.pendingContextClosures = new Map();
 
         // Background wakeup service status (instance-level, tracks this.page)
         // Prevents multiple BackgroundWakeup instances from running simultaneously
@@ -148,7 +151,33 @@ class BrowserManager {
      * @param {ConnectionRegistry} connectionRegistry - The ConnectionRegistry instance
      */
     setConnectionRegistry(connectionRegistry) {
+        if (this.connectionRegistry && this._onAuthQueuesDrained) {
+            this.connectionRegistry.off("authQueuesDrained", this._onAuthQueuesDrained);
+        }
         this.connectionRegistry = connectionRegistry;
+        if (this.connectionRegistry) {
+            this._onAuthQueuesDrained = authIndex => {
+                this._closePendingContextIfIdle(authIndex).catch(error => {
+                    this.logger.error(
+                        `[ContextPool] Failed to close pending context #${authIndex} after queue drain: ${error.message}`
+                    );
+                });
+            };
+            this.connectionRegistry.on("authQueuesDrained", this._onAuthQueuesDrained);
+        }
+    }
+
+    setSystemBusyProvider(provider) {
+        this._isSystemBusyProvider = typeof provider === "function" ? provider : null;
+    }
+
+    _isSystemBusy() {
+        try {
+            return this._isSystemBusyProvider?.() === true;
+        } catch (error) {
+            this.logger.warn(`[ContextPool] Failed to read system busy state: ${error.message}`);
+            return false;
+        }
     }
 
     /**
@@ -1532,6 +1561,109 @@ class BrowserManager {
             });
     }
 
+    _hasActiveQueueForAuth(authIndex) {
+        if (this.connectionRegistry?.hasMessageQueueForAuth) {
+            return this.connectionRegistry.hasMessageQueueForAuth(authIndex);
+        }
+        return false;
+    }
+
+    _cancelPendingContextClosure(authIndex, reason = "closure_cancelled") {
+        if (!this.pendingContextClosures.has(authIndex)) {
+            return false;
+        }
+        this.pendingContextClosures.delete(authIndex);
+        this.logger.info(`[ContextPool] Cancelled pending close for context #${authIndex} (${reason}).`);
+        return true;
+    }
+
+    _scheduleContextClosureWhenIdle(authIndex, reason) {
+        if (!this.contexts.has(authIndex)) {
+            return false;
+        }
+        const existingReason = this.pendingContextClosures.get(authIndex);
+        if (existingReason) {
+            this.logger.debug(
+                `[ContextPool] Context #${authIndex} is already pending close (${existingReason}), active queues are still present`
+            );
+            return false;
+        }
+        this.pendingContextClosures.set(authIndex, reason);
+        this.logger.info(
+            `[ContextPool] Deferring close for busy context #${authIndex} (active queue(s) present, reason: ${reason})`
+        );
+        return false;
+    }
+
+    async _closeContextForPoolIfPossible(authIndex, reason) {
+        if (this._hasActiveQueueForAuth(authIndex)) {
+            return this._scheduleContextClosureWhenIdle(authIndex, reason);
+        }
+
+        this.pendingContextClosures.delete(authIndex);
+        await this.closeContext(authIndex);
+        return true;
+    }
+
+    async _closePendingContextIfIdle(authIndex) {
+        if (!this.pendingContextClosures.has(authIndex)) {
+            return false;
+        }
+        if (authIndex === this._currentAuthIndex) {
+            this.logger.debug(
+                `[ContextPool] Skipping pending close for context #${authIndex} because it is active again as current.`
+            );
+            return false;
+        }
+        if (!this.contexts.has(authIndex)) {
+            this.pendingContextClosures.delete(authIndex);
+            return false;
+        }
+
+        if (this._hasActiveQueueForAuth(authIndex)) {
+            this.logger.debug(
+                `[ContextPool] Pending close for context #${authIndex} is still waiting on active queue(s).`
+            );
+            return false;
+        }
+
+        const pendingReason = this.pendingContextClosures.get(authIndex);
+        this.pendingContextClosures.delete(authIndex);
+        this.logger.info(
+            `[ContextPool] Closing deferred context #${authIndex} now that all queues are drained (reason: ${pendingReason}).`
+        );
+        await this.closeContext(authIndex);
+        if (this._isSystemBusy()) {
+            this.logger.info("[ContextPool] Skipping rebalance after deferred close because system is busy.");
+            return true;
+        }
+        this.rebalanceContextPool().catch(error => {
+            this.logger.error(`[ContextPool] Rebalance after deferred close failed: ${error.message}`);
+        });
+        return true;
+    }
+
+    async _flushPendingContextClosures() {
+        for (const authIndex of [...this.pendingContextClosures.keys()]) {
+            await this._closePendingContextIfIdle(authIndex);
+        }
+    }
+
+    _prioritizeContextsForRemoval(indices) {
+        const idle = [];
+        const busy = [];
+
+        for (const authIndex of indices) {
+            if (this._hasActiveQueueForAuth(authIndex)) {
+                busy.push({ authIndex });
+            } else {
+                idle.push(authIndex);
+            }
+        }
+
+        return { busy, idle };
+    }
+
     /**
      * Internal method to execute the actual preload task
      * @private
@@ -1754,15 +1886,28 @@ class BrowserManager {
             }
         }
 
-        // Remove contexts according to priority until we have enough space
-        const toRemove = removalPriority.slice(0, removeCount);
+        const { busy, idle } = this._prioritizeContextsForRemoval(removalPriority);
+        const toRemoveNow = idle.slice(0, removeCount);
+        const toDefer = busy.slice(0, Math.max(0, removeCount - toRemoveNow.length));
 
         this.logger.info(
-            `[ContextPool] Pre-cleanup: removing ${toRemove.length} contexts before switch to #${targetAuthIndex}: [${toRemove}] (${this.contexts.size} ready + ${this.initializingContexts.size} initializing)`
+            `[ContextPool] Pre-cleanup before switch to #${targetAuthIndex}: immediate=[${toRemoveNow}], deferred=[${toDefer.map(
+                entry => entry.authIndex
+            )}] (${this.contexts.size} ready + ${this.initializingContexts.size} initializing)`
         );
 
-        for (const idx of toRemove) {
-            await this.closeContext(idx);
+        for (const idx of toRemoveNow) {
+            await this._closeContextForPoolIfPossible(idx, "pre_cleanup_for_switch");
+        }
+
+        for (const entry of toDefer) {
+            this._scheduleContextClosureWhenIdle(entry.authIndex, "pre_cleanup_for_switch");
+        }
+
+        if (toDefer.length > 0) {
+            this.logger.warn(
+                `[ContextPool] Allowing temporary MAX_CONTEXTS overflow while busy contexts drain before switch to #${targetAuthIndex}.`
+            );
         }
     }
 
@@ -1796,6 +1941,10 @@ class BrowserManager {
             targets = new Set(ordered.slice(0, maxContexts));
         }
 
+        for (const idx of targets) {
+            this._cancelPendingContextClosure(idx, "rebalance_target");
+        }
+
         // Remove contexts not in targets (except current)
         // Special handling: if current account is a duplicate (old version), also remove its canonical version
         // BUT only in limited mode - in unlimited mode, keep all contexts
@@ -1835,16 +1984,25 @@ class BrowserManager {
         // If a foreground task is running, _executePreloadTask will skip it (line 1382)
         const candidates = ordered.filter(idx => !activeContexts.has(idx));
 
+        const { busy, idle } = this._prioritizeContextsForRemoval(toRemove);
+
         this.logger.info(
-            `[ContextPool] Rebalance: targets=[${[...targets]}], remove=[${toRemove}], candidates=[${candidates}]`
+            `[ContextPool] Rebalance: targets=[${[...targets]}], removeNow=[${idle}], removeDeferred=[${busy.map(
+                entry => entry.authIndex
+            )}], candidates=[${candidates}]`
         );
 
-        for (const idx of toRemove) {
-            await this.closeContext(idx);
+        for (const idx of idle) {
+            await this._closeContextForPoolIfPossible(idx, "rebalance");
+        }
+
+        for (const entry of busy) {
+            this._scheduleContextClosureWhenIdle(entry.authIndex, "rebalance");
         }
 
-        // Preload candidates if we have room in the pool
-        if (candidates.length > 0 && (isUnlimited || this.contexts.size < maxContexts)) {
+        // Preload candidates if ready and initializing contexts still leave room in the pool
+        const poolOccupancy = this.contexts.size + this.initializingContexts.size;
+        if (candidates.length > 0 && (isUnlimited || poolOccupancy < maxContexts)) {
             this._preloadBackgroundContexts(candidates, isUnlimited ? 0 : maxContexts);
         }
     }
@@ -2115,6 +2273,8 @@ class BrowserManager {
             throw new Error(`Invalid authIndex: ${authIndex}. Must be >= 0.`);
         }
 
+        this._cancelPendingContextClosure(authIndex, "context_reused");
+
         // [Auth Switch] Save current auth data before switching
         if (this.browser && this._currentAuthIndex >= 0 && this._currentAuthIndex !== authIndex) {
             try {
@@ -2194,6 +2354,7 @@ class BrowserManager {
 
                         // Switch to new context
                         this._activateContext(contextData.context, contextData.page, authIndex);
+                        await this._flushPendingContextClosures();
 
                         this.logger.info(`✅ [FastSwitch] Switched to account #${authIndex} instantly!`);
                         return;
@@ -2249,6 +2410,7 @@ class BrowserManager {
             const { context, page } = await this._initializeContext(authIndex, false);
 
             this._activateContext(context, page, authIndex);
+            await this._flushPendingContextClosures();
 
             // If this account was marked as expired but login succeeded, restore it
             if (this.authSource.isExpired(authIndex)) {
@@ -2456,6 +2618,8 @@ class BrowserManager {
      * @param {number} authIndex - The auth index to close
      */
     async closeContext(authIndex) {
+        this.pendingContextClosures.delete(authIndex);
+
         // If context is being initialized in background, signal abort and wait
         if (this.initializingContexts.has(authIndex)) {
             this.logger.info(`[Browser] Context #${authIndex} is being initialized, marking for abort and waiting...`);
@@ -2549,6 +2713,7 @@ class BrowserManager {
         this.contexts.clear();
         this.initializingContexts.clear();
         this.abortedContexts.clear();
+        this.pendingContextClosures.clear();
         this._wsInitState.clear();
         this.context = null;
         this.page = null;

src/core/ConnectionRegistry.js

@@ -309,13 +309,19 @@ class ConnectionRegistry extends EventEmitter {
 
     getConnectionByAuth(authIndex, log = true) {
         const connection = this.connectionsByAuth.get(authIndex);
-        if (connection && log) {
+
+        if (!log) {
+            return connection;
+        }
+
+        if (connection) {
             this.logger.debug(`[Registry] Found WebSocket connection for authIndex=${authIndex}`);
         } else if (this.logger.getLevel?.() === "DEBUG") {
             this.logger.debug(
                 `[Registry] No WebSocket connection found for authIndex=${authIndex}. Available: [${Array.from(this.connectionsByAuth.keys()).join(", ")}]`
             );
         }
+
         return connection;
     }
 
@@ -426,6 +432,7 @@ class ConnectionRegistry extends EventEmitter {
         // This prevents stale queues from lingering when retrying failed requests
         const existingEntry = this.messageQueues.get(requestId);
         if (existingEntry) {
+            const existingAuthIndex = existingEntry.authIndex;
             this.logger.debug(
                 `[Registry] Found existing message queue for request ${requestId} (authIndex=${existingEntry.authIndex}), closing it before creating new one`
             );
@@ -435,6 +442,9 @@ class ConnectionRegistry extends EventEmitter {
                 this.logger.debug(`[Registry] Failed to close existing queue for ${requestId}: ${e.message}`);
             }
             this.messageQueues.delete(requestId);
+            if (existingAuthIndex !== authIndex) {
+                this._emitAuthQueuesDrainedIfNeeded(existingAuthIndex);
+            }
         }
 
         const queue = new MessageQueue();
@@ -456,8 +466,10 @@ class ConnectionRegistry extends EventEmitter {
     removeMessageQueue(requestId, reason = "handler_cleanup") {
         const entry = this.messageQueues.get(requestId);
         if (entry) {
+            const authIndex = entry.authIndex;
             entry.queue.close(reason);
             this.messageQueues.delete(requestId);
+            this._emitAuthQueuesDrainedIfNeeded(authIndex);
         }
     }
 
@@ -481,6 +493,20 @@ class ConnectionRegistry extends EventEmitter {
         return entry ? entry.requestAttemptId || null : null;
     }
 
+    /**
+     * Check whether a specific account has any active message queue.
+     * @param {number} authIndex - The account index to inspect
+     * @returns {boolean} True if at least one active message queue belongs to the account
+     */
+    hasMessageQueueForAuth(authIndex) {
+        for (const entry of this.messageQueues.values()) {
+            if (entry.authIndex === authIndex) {
+                return true;
+            }
+        }
+        return false;
+    }
+
     /**
      * Close all message queues belonging to a specific account
      * @param {number} authIndex - The account whose queues should be closed
@@ -504,6 +530,7 @@ class ConnectionRegistry extends EventEmitter {
             this.logger.info(
                 `[Registry] Force closed ${count} pending message queue(s) for account #${authIndex} (reason: ${reason})`
             );
+            this._emitAuthQueuesDrainedIfNeeded(authIndex);
         }
         return count;
     }
@@ -548,6 +575,7 @@ class ConnectionRegistry extends EventEmitter {
                     this.logger.debug(`[Registry] Failed to close stale queue for ${requestId}: ${e.message}`);
                 }
                 this.messageQueues.delete(requestId);
+                this._emitAuthQueuesDrainedIfNeeded(entry.authIndex);
                 cleanedCount++;
             }
         }
@@ -559,6 +587,15 @@ class ConnectionRegistry extends EventEmitter {
         return cleanedCount;
     }
 
+    _emitAuthQueuesDrainedIfNeeded(authIndex) {
+        if (!Number.isInteger(authIndex) || authIndex < 0) {
+            return;
+        }
+        if (!this.hasMessageQueueForAuth(authIndex)) {
+            this.emit("authQueuesDrained", authIndex);
+        }
+    }
+
     /**
      * Safely close a WebSocket connection with readyState check
      * @param {WebSocket} ws - The WebSocket to close

src/core/ProxyServerSystem.js

@@ -111,6 +111,7 @@ class ProxyServerSystem extends EventEmitter {
             this.config,
             this.authSource
         );
+        this.browserManager.setSystemBusyProvider(() => this.requestHandler?.isSystemBusy === true);
 
         this.httpServer = null;
         this.wsServer = null;