fix(thread-channel): a refused value never reaches the buffer

CHANGELOG.md

@@ -5,6 +5,12 @@ All notable changes to the Async extension for PHP will be documented in this fi
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
+## [Unreleased]
+
+### Fixed
+
+- **Sending a value that cannot cross a thread boundary aborted the process instead of only throwing.** `ThreadChannel::send()` transfers its argument into persistent memory before it takes the lock, and the transfer refuses what it cannot copy — a resource, an object with dynamic properties — by releasing the partial graph, leaving the destination `IS_UNDEF` and throwing. The send did not check for that: it pushed the undefined slot into the buffer and reported success, so the caller got the right exception while the buffer held a value no receiver can interpret. `ThreadPool` reads the task as an array, so a debug build died on the assertion at `thread_pool.c:347` and a release build, where that assertion is compiled out, reads array fields from a value that is not one. The send now leaves the buffer untouched and returns false, which every caller already handles: `ThreadChannel::send()` rethrows, and `ThreadPool::submit()` and `map()` release the snapshot and the future first. Reproduced with `$pool->submit(fn () => 1, fopen('php://memory', 'r'))`: SIGABRT before, a caught `Error` and exit 0 after.
+
 ## [0.9.3] - 2026-08-13
 
 ### Fixed

tests/thread_channel/045-send_refused_value_not_buffered.phpt

@@ -0,0 +1,39 @@
+--TEST--
+ThreadChannel: a refused value never reaches the buffer
+--SKIPIF--
+<?php
+if (!PHP_ZTS) die('skip ZTS required');
+?>
+--FILE--
+<?php
+
+use Async\ThreadChannel;
+
+// A resource cannot cross a thread boundary: send() throws and leaves the channel
+// as it was, because a receiver cannot tell an undefined slot from a message.
+$ch = new ThreadChannel(4);
+
+try {
+    $ch->send(fopen('php://memory', 'r'));
+} catch (Error $e) {
+    echo "Caught: " . $e->getMessage() . "\n";
+}
+
+echo "count: " . $ch->count() . "\n";
+echo "empty: " . var_export($ch->isEmpty(), true) . "\n";
+
+// The channel stays usable for a value that can be transferred.
+$ch->send(['ok' => 1]);
+var_dump($ch->recv());
+
+echo "Done\n";
+?>
+--EXPECT--
+Caught: Cannot transfer a resource between threads
+count: 0
+empty: true
+array(1) {
+  ["ok"]=>
+  int(1)
+}
+Done

thread.h

@@ -163,6 +163,10 @@ typedef zend_async_thread_transfer_ctx_t thread_transfer_ctx_t;
  * Copy a zval into persistent memory for cross-thread transfer.
  * Deep copies strings, arrays, and objects. Preserves identity
  * (shared references → shared copies) and handles cycles.
+ *
+ * A value it cannot copy (resource, object with dynamic properties) is refused:
+ * the partial copy is released, *dst is left IS_UNDEF and an exception thrown.
+ * Test *dst, not EG(exception): one may have been pending before the call.
  */
 void async_thread_transfer_zval(zval *dst, const zval *src);
 

thread_channel.c

@@ -104,6 +104,14 @@ static bool thread_channel_send(zend_async_channel_t *channel, zval *value)
 	zval persistent_copy;
 	async_thread_transfer_zval(&persistent_copy, value);
 
+	if (UNEXPECTED(Z_TYPE(persistent_copy) == IS_UNDEF)) {
+		/* The value is not transferable between threads. async_thread_transfer_zval
+		 * has already released the partial graph and thrown; leave the buffer
+		 * untouched, because a receiver has no way to tell an undefined slot from
+		 * a real message and every reader asserts on the type it expects. */
+		return false;
+	}
+
 retry:
 	ASYNC_MUTEX_LOCK(ch->mutex);