'elem-array::connect' should always return 0 when the connection-slot is full.

src/ipc.cpp

@@ -422,6 +422,12 @@ static bool send(F&& gen_push, ipc::handle_t h, void const * data, std::size_t s
         ipc::error("fail: send, queue_of(h)->elems() == nullptr\n");
         return false;
     }
+    /**
+     * If the que hasn't connected as a receiver, the 'connected-id' must be 0,
+     * and 'connections' equals to 0 only if there are no receivers.
+     * Or if the que has connected as a receiver,
+     * 'connections' equals to 'connected-id' of this que only if there are no other receivers.
+    */
     if (que->elems()->connections(std::memory_order_relaxed) == que->connected_id()) {
         // there is no receiver on this connection
         return false;

src/libipc/circ/elem_def.h

@@ -23,9 +23,9 @@ constexpr u1_t index_of(u2_t c) noexcept {
 }
 
 class conn_head {
-    std::atomic<cc_t> cc_; // connections
+    std::atomic<cc_t> cc_{0}; // connections
     ipc::spin_lock lc_;
-    std::atomic<bool> constructed_;
+    std::atomic<bool> constructed_{false};
 
 public:
     void init() {
@@ -47,6 +47,10 @@ public:
         for (unsigned k = 0;;) {
             cc_t curr = cc_.load(std::memory_order_acquire);
             cc_t next = curr | (curr + 1); // find the first 0, and set it to 1.
+            if (next == 0) {
+                // connection-slot is full.
+                return 0;
+            }
             if (cc_.compare_exchange_weak(curr, next, std::memory_order_release)) {
                 return next ^ curr; // return connected id
             }

test/test_queue.cpp

@@ -127,6 +127,20 @@ TEST(Queue, check_size) {
     std::cout << "sizeof(elems_t<s, m, b>) = " << sizeof(el_t) << std::endl;
 }
 
+TEST(Queue, connection) {
+    {
+        using el_t = elems_t<ipc::relat::single, ipc::relat::multi, ipc::trans::broadcast>;
+        el_t el;
+        el.init();
+        for (std::size_t i = 0; i < (sizeof(ipc::circ::cc_t) * CHAR_BIT); ++i) {
+            EXPECT_NE(el.connect(), 0);
+        }
+        for (std::size_t i = 0; i < 10000; ++i) {
+            EXPECT_EQ(el.connect(), 0);
+        }
+    }
+}
+
 TEST(Queue, prod_cons_1v1_unicast) {
     test_sr(elems_t<ipc::relat::single, ipc::relat::single, ipc::trans::unicast> {}, 1, 1, "ssu");
     test_sr(elems_t<ipc::relat::single, ipc::relat::multi , ipc::trans::unicast> {}, 1, 1, "smu");