Implement event loop timers.

GObjects can now register a timer with the GEventLoop. This will eventually
cause GTimerEvents to be dispatched to the GObject.

This needed a few supporting changes in the kernel:

- The PIT now ticks 1000 times/sec.
- select() now supports an arbitrary timeout.
- gettimeofday() now returns something in the tv_usec field.

With these changes, the clock window in guitest2 finally ticks on its own.

Kernel/Process.cpp

@@ -1442,7 +1442,7 @@ int Process::sys$gettimeofday(timeval* tv)
     InterruptDisabler disabler;
     auto now = RTC::now();
     tv->tv_sec = now;
-    tv->tv_usec = 0;
+    tv->tv_usec = PIT::ticks_since_boot() % 1000;
     return 0;
 }
 
@@ -1976,8 +1976,12 @@ int Process::sys$select(const Syscall::SC_select_params* params)
     // FIXME: Implement exceptfds support.
     ASSERT(!exceptfds);
 
-    // FIXME: Implement timeout support.
-    ASSERT(!timeout || (!timeout->tv_sec && !timeout->tv_usec));
+    if (timeout) {
+        m_select_timeout = *timeout;
+        m_select_has_timeout = true;
+    } else {
+        m_select_has_timeout = false;
+    }
 
     if (nfds < 0)
         return -EINVAL;

Kernel/Process.h

@@ -331,6 +331,8 @@ private:
     int m_blocked_fd { -1 };
     Vector<int> m_select_read_fds;
     Vector<int> m_select_write_fds;
+    timeval m_select_timeout;
+    bool m_select_has_timeout { false };
     size_t m_max_open_file_descriptors { 16 };
     SignalActionData m_signal_action_data[32];
     dword m_pending_signals { 0 };

Kernel/Scheduler.cpp

@@ -1,6 +1,8 @@
 #include "Scheduler.h"
 #include "Process.h"
 #include "system.h"
+#include "RTC.h"
+#include "i8253.h"
 
 //#define LOG_EVERY_CONTEXT_SWITCH
 //#define SCHEDULER_DEBUG
@@ -29,7 +31,7 @@ bool Scheduler::pick_next()
     }
 
     // Check and unblock processes whose wait conditions have been met.
-    Process::for_each([] (auto& process) {
+    Process::for_each([] (Process& process) {
         if (process.state() == Process::BlockedSleep) {
             if (process.wakeup_time() <= system.uptime)
                 process.unblock();
@@ -71,6 +73,14 @@ bool Scheduler::pick_next()
                 process.unblock();
                 return true;
             }
+            if (process.m_select_has_timeout) {
+                auto now_sec = RTC::now();
+                auto now_usec = PIT::ticks_since_boot() % 1000;
+                if (now_sec > process.m_select_timeout.tv_sec || (now_sec == process.m_select_timeout.tv_sec && now_usec >= process.m_select_timeout.tv_usec)) {
+                    process.unblock();
+                    return true;
+                }
+            }
             for (int fd : process.m_select_read_fds) {
                 if (process.m_fds[fd].descriptor->can_read(process)) {
                     process.unblock();

Kernel/i8253.cpp

@@ -57,16 +57,26 @@ asm(
 
 #define BASE_FREQUENCY     1193182
 
+static dword s_ticks_since_boot;
+
 void timer_interrupt_handler(RegisterDump& regs)
 {
     IRQHandlerScope scope(IRQ_TIMER);
+    ++s_ticks_since_boot;
     Scheduler::timer_tick(regs);
 }
 
 namespace PIT {
 
+dword ticks_since_boot()
+{
+    return s_ticks_since_boot;
+}
+
 void initialize()
 {
+    s_ticks_since_boot = 0;
+
     word timer_reload;
 
     IO::out8(PIT_CTL, TIMER0_SELECT | WRITE_WORD | MODE_SQUARE_WAVE);

Kernel/i8253.h

@@ -1,9 +1,12 @@
 #pragma once
 
-#define TICKS_PER_SECOND          600
+#include <AK/Types.h>
+
+#define TICKS_PER_SECOND          1000
 
 namespace PIT {
 
 void initialize();
+dword ticks_since_boot();
 
 }