rt: Simplify channel-port association

It turns out that there's only ever a single channel per port these days,
and it always has the same lifetime as the port, so we don't need a list or a
complex association protocol.

src/rt/rust_builtin.cpp

@@ -538,9 +538,8 @@ port_recv(uintptr_t *dptr, rust_port *port) {
         scoped_lock with(port->lock);
 
         LOG(task, comm, "port: 0x%" PRIxPTR ", dptr: 0x%" PRIxPTR
-            ", size: 0x%" PRIxPTR ", chan_no: %d",
-            (uintptr_t) port, (uintptr_t) dptr, port->unit_sz,
-            port->chans.length());
+            ", size: 0x%" PRIxPTR,
+            (uintptr_t) port, (uintptr_t) dptr, port->unit_sz);
 
         if (port->receive(dptr)) {
             return;

src/rt/rust_chan.cpp

@@ -6,16 +6,17 @@
  */
 rust_chan::rust_chan(rust_kernel *kernel, rust_port *port,
                      size_t unit_sz)
-    : ref_count(1),
+    : ref_count(0),
       kernel(kernel),
       port(port),
       buffer(kernel, unit_sz) {
-    if (port) {
-        associate(port);
-    }
     KLOG(kernel, comm, "new rust_chan(task=0x%" PRIxPTR
         ", port=0x%" PRIxPTR ") -> chan=0x%" PRIxPTR,
         (uintptr_t) task, (uintptr_t) port, (uintptr_t) this);
+
+    A(kernel, port != NULL, "Port must not be null");
+    this->task = port->task;
+    this->task->ref();
 }
 
 rust_chan::~rust_chan() {
@@ -26,49 +27,15 @@ rust_chan::~rust_chan() {
 
     A(kernel, is_associated() == false,
       "Channel must be disassociated before being freed.");
-}
 
-/**
- * Link this channel with the specified port.
- */
-void rust_chan::associate(rust_port *port) {
-    this->ref();
-    this->port = port;
-    scoped_lock with(port->lock);
-    KLOG(kernel, task,
-         "associating chan: 0x%" PRIxPTR " with port: 0x%" PRIxPTR,
-         this, port);
-    this->task = port->task;
-    this->task->ref();
-    this->port->chans.push(this);
+    task->deref();
+    task = NULL;
 }
 
 bool rust_chan::is_associated() {
     return port != NULL;
 }
 
-/**
- * Unlink this channel from its associated port.
- */
-void rust_chan::disassociate() {
-    A(kernel,
-      port->lock.lock_held_by_current_thread(),
-      "Port referent lock must be held to call rust_chan::disassociate");
-    A(kernel, is_associated(),
-      "Channel must be associated with a port.");
-    KLOG(kernel, task,
-         "disassociating chan: 0x%" PRIxPTR " from port: 0x%" PRIxPTR,
-         this, port);
-    task->deref();
-    this->task = NULL;
-    port->chans.swap_delete(this);
-
-    // Delete reference to the port.
-    port = NULL;
-
-    this->deref();
-}
-
 /**
  * Attempt to send data to the associated port.
  */

src/rt/rust_chan.h

@@ -16,8 +16,6 @@ public:
     size_t idx;
     circular_buffer buffer;
 
-    void associate(rust_port *port);
-    void disassociate();
     bool is_associated();
 
     void send(void *sptr);

src/rt/rust_port.cpp

@@ -5,7 +5,7 @@
 
 rust_port::rust_port(rust_task *task, size_t unit_sz)
     : ref_count(1), kernel(task->kernel), task(task),
-      unit_sz(unit_sz), writers(task), chans(task) {
+      unit_sz(unit_sz), writers(task) {
 
     LOG(task, comm,
         "new rust_port(task=0x%" PRIxPTR ", unit_sz=%d) -> port=0x%"
@@ -14,47 +14,37 @@ rust_port::rust_port(rust_task *task, size_t unit_sz)
     id = task->register_port(this);
     remote_chan = new (task->kernel, "rust_chan")
         rust_chan(task->kernel, this, unit_sz);
+    remote_chan->ref();
+    remote_chan->port = this;
 }
 
 rust_port::~rust_port() {
     LOG(task, comm, "~rust_port 0x%" PRIxPTR, (uintptr_t) this);
 
-    // Disassociate channels from this port.
-    while (chans.is_empty() == false) {
+    {
         scoped_lock with(lock);
-        rust_chan *chan = chans.peek();
-        chan->disassociate();
+        remote_chan->port = NULL;
+        remote_chan->deref();
+        remote_chan = NULL;
     }
 
-    remote_chan->deref();
-    remote_chan = NULL;
-
     task->release_port(id);
 }
 
 bool rust_port::receive(void *dptr) {
-    for (uint32_t i = 0; i < chans.length(); i++) {
-        rust_chan *chan = chans[i];
-        if (chan->buffer.is_empty() == false) {
-            chan->buffer.dequeue(dptr);
-            LOG(task, comm, "<=== read data ===");
-            return true;
-        }
+    if (remote_chan->buffer.is_empty() == false) {
+        remote_chan->buffer.dequeue(dptr);
+        LOG(task, comm, "<=== read data ===");
+        return true;
     }
     return false;
 }
 
 void rust_port::log_state() {
     LOG(task, comm,
-              "rust_port: 0x%" PRIxPTR ", associated channel(s): %d",
-              this, chans.length());
-    for (uint32_t i = 0; i < chans.length(); i++) {
-        rust_chan *chan = chans[i];
-        LOG(task, comm,
-            "\tchan: 0x%" PRIxPTR ", size: %d",
-            chan,
-            chan->buffer.size());
-    }
+        "\tchan: 0x%" PRIxPTR ", size: %d",
+        remote_chan,
+        remote_chan->buffer.size());
 }
 
 //

src/rt/rust_port.h

@@ -12,7 +12,6 @@ public:
     rust_chan *remote_chan;
     size_t unit_sz;
     ptr_vec<rust_token> writers;
-    ptr_vec<rust_chan> chans;
 
     lock_and_signal lock;