Introducing mutex

nx/include/switch.h

@@ -15,6 +15,7 @@ extern "C" {
 #include <switch/heap.h>
 
 #include <switch/kernel/tmem.h>
+#include <switch/kernel/mutex.h>
 
 #include <switch/services/sm.h>
 #include <switch/services/bsd.h>

nx/include/switch/kernel/mutex.h

@@ -0,0 +1,16 @@
+// Copyright 2017 plutoo
+typedef struct {
+    u32 Tag;
+} Mutex;
+
+typedef struct {
+    u32    Owner;
+    Mutex  Lock;
+    size_t Count;
+} RMutex;
+
+void mutexLock(Mutex* m);
+void mutexUnlock(Mutex* m);
+
+void rmutexLock(RMutex* m);
+void rmutexUnlock(RMutex* m);

nx/include/switch/svc.h

@@ -48,6 +48,8 @@ Result svcSleepThread(u64 nano);
 Result svcCloseHandle(Handle handle);
 Result svcCreateTransferMemory(Handle* out, void* addr, size_t size, u32 perm);
 Result svcWaitSynchronization(s32* index, const Handle* handles, s32 handleCount, u64 timeout);
+Result svcArbitrateLock(u32 wait_tag, u32* tag_location, u32 self_tag);
+Result svcArbitrateUnlock(u32* tag_location);
 Result svcConnectToNamedPort(Handle* session, const char* name);
 Result svcSendSyncRequest(Handle session);
 Result svcBreak(u32 breakReason, u64 inval1, u64 inval2);

nx/source/kernel/mutex.c

@@ -0,0 +1,74 @@
+// Copyright 2017 plutoo
+#include <switch.h>
+
+#define HAS_LISTENERS 0x40000000
+
+static u32 _GetTag() {
+    // todo: Needs filling in at thread creation.
+    // todo: Must always be assigned non-zero.
+    return ((u32*)armGetTls()) [0x1FC/4];
+}
+
+void mutexLock(Mutex* m) {
+    u32 self = _GetTag();
+    u32 cur = __sync_val_compare_and_swap(&m->Tag, 0, self);
+
+    if (cur == 0) {
+        // We won the race!
+        return;
+    }
+
+    while (1) {
+        if ((cur &~ HAS_LISTENERS) == self) {
+            // Kernel assigned it to us!
+            return;
+        }
+
+        if (cur & HAS_LISTENERS) {
+            // The flag is already set, we can use the syscall.
+            svcArbitrateLock(cur &~ HAS_LISTENERS, &m->Tag, self);
+        }
+        else {
+            // The flag is not set, we need to set it.
+            u32 old = __sync_val_compare_and_swap(&m->Tag, cur, cur | HAS_LISTENERS);
+
+            if (old == cur) {
+                // Flag was set successfully.
+                svcArbitrateLock(cur &~ HAS_LISTENERS, &m->Tag, self);
+            }
+        }
+
+        cur = __sync_val_compare_and_swap(&m->Tag, 0, self);
+
+        if (cur == 0) {
+            // We won the race!
+            return;
+        }
+    }
+}
+
+void mutexUnlock(Mutex* m) {
+    u32 self = _GetTag();
+    u32 old = __sync_val_compare_and_swap(&m->Tag, self, 0);
+
+    if (old & HAS_LISTENERS) {
+        svcArbitrateUnlock(&m->Tag);
+    }
+}
+
+void rmutexLock(RMutex* m) {
+    if (m->Owner == _GetTag()) {
+        m->Count++;
+    }
+    else {
+        mutexLock(&m->Lock);
+        m->Owner = _GetTag();
+    }
+}
+
+void rmutexUnlock(RMutex* m) {
+    if (--m->Count == 0) {
+        m->Owner = 0;
+        mutexUnlock(&m->Lock);
+    }
+}

nx/source/kernel/svc.s

@@ -58,6 +58,14 @@ SVC_BEGIN svcWaitSynchronization
 	ret
 SVC_END
 
+SVC_BEGIN svcArbitrateLock
+    svc 0x1a
+SVC_END
+
+SVC_BEGIN svcArbitrateUnlock
+    svc 0x1b
+SVC_END
+
 SVC_BEGIN svcConnectToNamedPort
 	str x0, [sp, #-16]!
 	svc 0x1F