add condvar in kernel and app

os/src/sync/condvar.rs

@@ -0,0 +1,39 @@
+use alloc::{sync::Arc, collections::VecDeque};
+use crate::task::{add_task, TaskControlBlock, current_task, block_current_and_run_next};
+use crate::sync::{Mutex, UPSafeCell};
+
+pub struct Condvar {
+    pub inner: UPSafeCell<CondvarInner>,
+}
+
+pub struct CondvarInner {
+    pub wait_queue: VecDeque<Arc<TaskControlBlock>>,
+}
+
+impl Condvar {
+    pub fn new() -> Self {
+        Self {
+            inner: unsafe { UPSafeCell::new(
+                CondvarInner {
+                    wait_queue: VecDeque::new(),
+                }
+            )},
+        }
+    }
+
+    pub fn signal(&self) {
+        let mut inner = self.inner.exclusive_access();
+        if let Some(task) = inner.wait_queue.pop_front() {
+            add_task(task);
+        }
+    }
+
+    pub fn wait(&self, mutex:Arc<dyn Mutex>) {
+        mutex.unlock();
+        let mut inner = self.inner.exclusive_access();
+        inner.wait_queue.push_back(current_task().unwrap());
+        drop(inner);
+        block_current_and_run_next();
+        mutex.lock();
+    }
+}

os/src/sync/mod.rs

@@ -1,7 +1,9 @@
 mod up;
 mod mutex;
 mod semaphore;
+mod condvar;
 
 pub use up::UPSafeCell;
 pub use mutex::{Mutex, MutexSpin, MutexBlocking};
 pub use semaphore::Semaphore;
+pub use condvar::Condvar;