[uart] Make UART driver single-threaded

The design of the UART driver was needlessly multi-threaded and a source
of threading bugs. Just make it single-threaded.

src/user/drv.uart/main.cpp

@@ -10,7 +10,6 @@
 #include <j6/protocols/service_locator.h>
 #include <j6/syscalls.h>
 #include <j6/sysconf.h>
-#include <j6/thread.hh>
 #include <j6/types.h>
 #include <util/hash.h>
 
@@ -21,7 +20,6 @@ extern "C" {
     int main(int, const char **);
 }
 
-extern j6_handle_t __handle_self;
 j6_handle_t g_handle_sys = j6_handle_invalid;
 
 constexpr size_t in_buf_size = 512;
@@ -35,9 +33,36 @@ uint8_t com2_out[out_buf_size];
 constexpr uintptr_t stack_top = 0xf80000000;
 
 int
-channel_pump_loop(serial_port *com1)
+main(int argc, const char **argv)
 {
-    j6_status_t result;
+    j6_log("uart driver starting");
+
+    j6_handle_t event = j6_handle_invalid;
+    j6_status_t result = j6_status_ok;
+
+    g_handle_sys = j6_find_first_handle(j6_object_type_system);
+    if (g_handle_sys == j6_handle_invalid)
+        return 1;
+
+    result = j6_system_request_iopl(g_handle_sys, 3);
+    if (result != j6_status_ok)
+        return result;
+
+    result = j6_event_create(&event);
+    if (result != j6_status_ok)
+        return result;
+
+    result = j6_system_bind_irq(g_handle_sys, event, 3, 0);
+    if (result != j6_status_ok)
+        return result;
+
+    result = j6_system_bind_irq(g_handle_sys, event, 4, 1);
+    if (result != j6_status_ok)
+        return result;
+
+    serial_port com1 {COM1, in_buf_size, com1_in, out_buf_size, com1_out};
+    serial_port com2 {COM2, in_buf_size, com2_in, out_buf_size, com2_out};
+
     static constexpr size_t buffer_size = 512;
     char buffer[buffer_size];
 
@@ -71,57 +96,10 @@ channel_pump_loop(serial_port *com1)
 
     while (true) {
         size_t size = buffer_size;
-        j6_status_t s = j6_channel_receive(cout, buffer, &size, j6_channel_block);
-        if (s == j6_status_ok)
-            com1->write(buffer, size);
-    }
-}
+        result = j6_channel_receive(cout, buffer, &size, 0);
+        if (result == j6_status_ok)
+            com1.write(buffer, size);
 
-void
-pump_proc(void *com_ptr)
-{
-    serial_port *com1 = reinterpret_cast<serial_port*>(com_ptr);
-    j6_process_exit(channel_pump_loop(com1));
-}
-
-int
-main(int argc, const char **argv)
-{
-    j6_log("uart driver starting");
-
-    j6_handle_t event = j6_handle_invalid;
-    j6_status_t result = j6_status_ok;
-
-    g_handle_sys = j6_find_first_handle(j6_object_type_system);
-    if (g_handle_sys == j6_handle_invalid)
-        return 1;
-
-    result = j6_system_request_iopl(g_handle_sys, 3);
-    if (result != j6_status_ok)
-        return result;
-
-    result = j6_event_create(&event);
-    if (result != j6_status_ok)
-        return result;
-
-    result = j6_system_bind_irq(g_handle_sys, event, 3, 0);
-    if (result != j6_status_ok)
-        return result;
-
-    result = j6_system_bind_irq(g_handle_sys, event, 4, 1);
-    if (result != j6_status_ok)
-        return result;
-
-    serial_port com1 {COM1, in_buf_size, com1_in, out_buf_size, com1_out};
-    serial_port com2 {COM2, in_buf_size, com2_in, out_buf_size, com2_out};
-
-    j6::thread pump_thread {pump_proc, stack_top};
-    result = pump_thread.start(&com1);
-    if (result != j6_status_ok)
-        return result;
-
-    size_t len = 0;
-    while (true) {
         uint64_t signals = 0;
         result = j6_event_wait(event, &signals, 100);
         if (result == j6_err_timed_out) {

src/user/drv.uart/serial.cpp

@@ -91,9 +91,7 @@ serial_port::do_write()
 {
     // If another thread is writing data, just give up and
     // try again later
-    util::scoped_trylock lock {m_lock};
-    if (!lock.locked())
-        return;
+    util::scoped_lock lock {m_lock};
 
     uint8_t *data = nullptr;
     size_t n = m_out_buffer.get_block(reinterpret_cast<void**>(&data));