Organize context module

kernel/context/switch.rs

@@ -0,0 +1,65 @@
+use core::sync::atomic::Ordering;
+
+use arch;
+use super::{contexts, Context, CONTEXT_ID};
+
+/// Switch to the next context
+///
+/// # Safety
+///
+/// Do not call this while holding locks!
+pub unsafe fn switch() {
+    use core::ops::DerefMut;
+
+    // Set the global lock to avoid the unsafe operations below from causing issues
+    while arch::context::CONTEXT_SWITCH_LOCK.compare_and_swap(false, true, Ordering::SeqCst) {
+        arch::interrupt::pause();
+    }
+
+    let from_ptr = {
+        let contexts = contexts();
+        let context_lock = contexts.current().expect("context::switch: Not inside of context");
+        let mut context = context_lock.write();
+        context.deref_mut() as *mut Context
+    };
+
+    let mut to_ptr = 0 as *mut Context;
+
+    for (pid, context_lock) in contexts().iter() {
+        if *pid > (*from_ptr).id {
+            let mut context = context_lock.write();
+            if ! context.running && ! context.blocked && ! context.exited {
+                to_ptr = context.deref_mut() as *mut Context;
+                break;
+            }
+        }
+    }
+
+    if to_ptr as usize == 0 {
+        for (pid, context_lock) in contexts().iter() {
+            if *pid < (*from_ptr).id {
+                let mut context = context_lock.write();
+                if ! context.running && ! context.blocked && ! context.exited {
+                    to_ptr = context.deref_mut() as *mut Context;
+                    break;
+                }
+            }
+        }
+    }
+
+    if to_ptr as usize == 0 {
+        // TODO: Sleep, wait for interrupt
+        // Unset global lock if no context found
+        arch::context::CONTEXT_SWITCH_LOCK.store(false, Ordering::SeqCst);
+        return;
+    }
+
+    (&mut *from_ptr).running = false;
+    (&mut *to_ptr).running = true;
+    if let Some(ref stack) = (*to_ptr).kstack {
+        arch::gdt::TSS.rsp[0] = (stack.as_ptr() as usize + stack.len() - 256) as u64;
+    }
+    CONTEXT_ID.store((&mut *to_ptr).id, Ordering::SeqCst);
+
+    (&mut *from_ptr).arch.switch_to(&mut (&mut *to_ptr).arch);
+}