From 52377a980c0f17fa9e4c218594b7d76afb60c8fe Mon Sep 17 00:00:00 2001
From: Ali Mashtizadeh <mashti@uwaterloo.ca>
Date: Wed, 30 Aug 2023 12:49:23 -0400
Subject: [PATCH] Add waitchannels into the kernel.

---
 sys/SConscript            |   1 +
 sys/amd64/machine.c       |   1 +
 sys/include/thread.h      |   4 ++
 sys/include/waitchannel.h |  27 ++++++++
 sys/kern/waitchannel.c    | 128 ++++++++++++++++++++++++++++++++++++++
 5 files changed, 161 insertions(+)
 create mode 100644 sys/include/waitchannel.h
 create mode 100644 sys/kern/waitchannel.c

diff --git a/sys/SConscript b/sys/SConscript
index 6a95684..ac2552a 100644
--- a/sys/SConscript
+++ b/sys/SConscript
@@ -62,6 +62,7 @@ src_common = [
     "kern/thread.c",
     "kern/vfs.c",
     "kern/vfsuio.c",
+    "kern/waitchannel.c",
     "dev/ahci.c",
     "dev/console.c",
     "dev/e1000.c",
diff --git a/sys/amd64/machine.c b/sys/amd64/machine.c
index c3aeb07..ebfd965 100644
--- a/sys/amd64/machine.c
+++ b/sys/amd64/machine.c
@@ -150,6 +150,7 @@ Machine_EarlyInit()
     Spinlock_EarlyInit();
     Critical_Init();
     Critical_Enter();
+    WaitChannel_EarlyInit();
     Console_Init();
     PAlloc_Init();
 }
diff --git a/sys/include/thread.h b/sys/include/thread.h
index bff2efc..f4037e0 100644
--- a/sys/include/thread.h
+++ b/sys/include/thread.h
@@ -5,6 +5,7 @@
 #include <sys/queue.h>
 #include <sys/handle.h>
 #include <sys/ktimer.h>
+#include <sys/waitchannel.h>
 
 struct Thread;
 typedef struct Thread Thread;
@@ -41,6 +42,9 @@ typedef struct Thread {
     KTimerEvent		*timerEvt;	// Timer event for wakeups
     uintptr_t		exitValue;
     TAILQ_ENTRY(Thread)	semaQueue;	// Semaphore Queue
+    // Wait Channels
+    WaitChannel		*chan;
+    TAILQ_ENTRY(Thread)	chanQueue;
     // Statistics
     uint64_t		ctxSwitches;
     uint64_t		userTime;
diff --git a/sys/include/waitchannel.h b/sys/include/waitchannel.h
new file mode 100644
index 0000000..23d5f48
--- /dev/null
+++ b/sys/include/waitchannel.h
@@ -0,0 +1,27 @@
+
+#ifndef __WAITCHANNEL_H__
+#define __WAITCHANNEL_H__
+
+#include <sys/cdefs.h>
+#include <sys/queue.h>
+
+#define WAITCHANNEL_NAMELEN    32
+
+typedef struct WaitChannel
+{
+    Spinlock				lock;
+    char				name[WAITCHANNEL_NAMELEN];
+    LIST_ENTRY(WaitChannel)		chanList;
+    TAILQ_HEAD(WaitQueue, Thread)	chanQueue;
+} WaitChannel;
+
+void WaitChannel_EarlyInit();
+void WaitChannel_Init(WaitChannel *lock, const char *name);
+void WaitChannel_Destroy(WaitChannel *lock);
+void WaitChannel_Lock(WaitChannel *lock) __LOCK_EX(lock->lock);
+void WaitChannel_Sleep(WaitChannel *lock) __UNLOCK_EX(lock->lock);
+void WaitChannel_Wake(WaitChannel *lock);
+void WaitChannel_WakeAll(WaitChannel *lock);
+
+#endif /* __WAITCHANNEL_H__ */
+
diff --git a/sys/kern/waitchannel.c b/sys/kern/waitchannel.c
new file mode 100644
index 0000000..941751b
--- /dev/null
+++ b/sys/kern/waitchannel.c
@@ -0,0 +1,128 @@
+
+#include <stdbool.h>
+#include <stdint.h>
+#include <string.h>
+
+#include <sys/cdefs.h>
+#include <sys/kassert.h>
+#include <sys/kdebug.h>
+#include <sys/queue.h>
+#include <sys/thread.h>
+#include <sys/spinlock.h>
+#include <sys/waitchannel.h>
+
+Spinlock chanListLock;
+LIST_HEAD(ChanListHead, WaitChannel) chanList = LIST_HEAD_INITIALIZER(chanList);
+
+void
+WaitChannel_EarlyInit()
+{
+    Spinlock_Init(&chanListLock, "WaitChannel List", SPINLOCK_TYPE_NORMAL);
+}
+
+void
+WaitChannel_Init(WaitChannel *wchan, const char *name)
+{
+    TAILQ_INIT(&wchan->chanQueue);
+    strncpy(&wchan->name[0], name, WAITCHANNEL_NAMELEN);
+    Spinlock_Init(&wchan->lock, name, SPINLOCK_TYPE_NORMAL);
+
+    Spinlock_Lock(&chanListLock);
+    LIST_INSERT_HEAD(&chanList, wchan, chanList);
+    Spinlock_Unlock(&chanListLock);
+}
+
+void
+WaitChannel_Destroy(WaitChannel *wchan)
+{
+    ASSERT(TAILQ_EMPTY(&wchan->chanQueue));
+
+    Spinlock_Lock(&chanListLock);
+    LIST_REMOVE(wchan, chanList);
+    Spinlock_Unlock(&chanListLock);
+
+    Spinlock_Destroy(&wchan->lock);
+}
+
+/*
+ * WaitChannel_Lock --
+ *
+ *	Acquires the wait channel lock.
+ */
+void
+WaitChannel_Lock(WaitChannel *wchan)
+{
+    Spinlock_Lock(&wchan->lock);
+}
+
+/*
+ * WaitChannel_Sleep --
+ *
+ *	Places the current thread to asleep while releasing the wait channel 
+ *	lock.
+ *
+ * Side Effect:
+ *	Retains a reference to thread until the thread is woken up.
+ */
+void
+WaitChannel_Sleep(WaitChannel *wchan)
+{
+    Thread *thr = Sched_Current();
+
+    Sched_SetWaiting(thr);
+    TAILQ_INSERT_TAIL(&wchan->chanQueue, thr, chanQueue);
+    Spinlock_Unlock(&wchan->lock);
+
+    Sched_Scheduler();
+}
+
+/*
+ * WaitChannel_Wake --
+ *
+ *	Wake up a single thread.
+ *
+ * Side Effects:
+ *	Releases the thread reference once complete.
+ */
+void
+WaitChannel_Wake(WaitChannel *wchan)
+{
+    Thread *thr;
+
+    Spinlock_Lock(&wchan->lock);
+
+    thr = TAILQ_FIRST(&wchan->chanQueue);
+    TAILQ_REMOVE(&wchan->chanQueue, thr, chanQueue);
+    Sched_SetRunnable(thr);
+    Thread_Release(thr);
+
+    Spinlock_Unlock(&wchan->lock);
+}
+
+/*
+ * WaitChannel_WakeAll --
+ *
+ *	Wakes up all threads currently sleeping on the wait channel.
+ *
+ * Side Effects:
+ *	Releases all thread references.
+ */
+void
+WaitChannel_WakeAll(WaitChannel *wchan)
+{
+    Thread *thr;
+    Thread *thrTemp;
+
+    Spinlock_Lock(&wchan->lock);
+
+    TAILQ_FOREACH_SAFE(thr, &wchan->chanQueue, chanQueue, thrTemp) {
+	thr = TAILQ_FIRST(&wchan->chanQueue);
+	TAILQ_REMOVE(&wchan->chanQueue, thr, chanQueue);
+	Sched_SetRunnable(thr);
+	Thread_Release(thr);
+    }
+
+    Spinlock_Unlock(&wchan->lock);
+
+}
+