channel.close时不再清空缓存, 以便于还可以继续读

Author: yuyangzi

libgo/routine_sync/channel.h

@@ -33,10 +33,7 @@ class ChannelImplWithSignal : public DebuggerId<ChannelImplWithSignal<int>>
         RS_DBG(dbg_channel, "channel=%ld | %s | ptr(t)=0x%p | isWait=%d | abstime=%d | closed=%d | popWaiting_=%p | pushWaiting_=%p",
             id(), __func__, (void*)&t, isWait, !!abstime, closed_, (void*)popWaiting_, (void*)pushWaiting_);
 
-        if (closed_)
-            return false;
-
-        if (pushWaiting_) {   // 有push协程在等待, 读出来 & 清理
+        if (pushWaiting_ && pushWaiting_ != (ConditionVariable*)kClosedWaiting) {   // 有push协程在等待, 读出来 & 清理
             t = *pushQ_;
             pushQ_ = nullptr;
 
@@ -51,6 +48,9 @@ class ChannelImplWithSignal : public DebuggerId<ChannelImplWithSignal<int>>
             return true;
         }
 
+        if (closed_)
+            return false;
+
         if (!isWait) {
             RS_DBG(dbg_channel, "channel=%ld | %s | not match && not wait | return false",
                 id(), __func__);
@@ -68,15 +68,16 @@ class ChannelImplWithSignal : public DebuggerId<ChannelImplWithSignal<int>>
             id(), __func__);
 
         (void)waiting.wait_until_p(lock, abstime, [&]{ return popWaiting_ != &waiting; });
-        bool ok = popWaiting_ != &waiting;
+        bool changed = (popWaiting_ != &waiting);
+        bool ok = changed && popWaiting_ != (ConditionVariable*)kClosedWaiting;
 
-        RS_DBG(dbg_channel, "channel=%ld | %s | waked | matched=%d",
-            id(), __func__, ok);
+        RS_DBG(dbg_channel, "channel=%ld | %s | waked | closed=%d | changed=%d | ok=%d",
+            id(), __func__, closed_, changed, ok);
 
         if (ok) {
             // 成功
             t = std::move(temp);    // 对外部T的写操作放到本线程来做, 降低使用难度
-        } else {
+        } else if (!changed) {
             // 超时，清理
             popQ_ = nullptr;
             popWaiting_ = nullptr;
@@ -93,13 +94,13 @@ class ChannelImplWithSignal : public DebuggerId<ChannelImplWithSignal<int>>
         RS_DBG(dbg_channel, "channel=%ld | %s | ptr(t)=0x%p | isWait=%d | abstime=%d | closed=%d | popWaiting_=%p | pushWaiting_=%p",
             id(), __func__, (void*)&t, isWait, !!abstime, closed_, (void*)popWaiting_, (void*)pushWaiting_);
 
+        if (closed_)
+            return false;
+
         if (!popWaiting_) {
             return pop_impl_with_signal_noqueued(t, isWait, abstime, lock);
         }
 
-        if (closed_)
-            return false;
-
         if (!isWait) {
             RS_DBG(dbg_channel, "channel=%ld | %s | pop contended && not wait | return false",
                 id(), __func__);
@@ -119,8 +120,12 @@ class ChannelImplWithSignal : public DebuggerId<ChannelImplWithSignal<int>>
             }
         }
 
-        RS_DBG(dbg_channel, "channel=%ld | %s | waked | pop idle",
-            id(), __func__);
+        RS_DBG(dbg_channel, "channel=%ld | %s | waked | closed=%d | pop idle",
+            id(), __func__, closed_);
+
+        if (closed_)
+            return false;
+
         return pop_impl_with_signal_noqueued(t, isWait, abstime, lock);
     }
 
@@ -132,10 +137,7 @@ class ChannelImplWithSignal : public DebuggerId<ChannelImplWithSignal<int>>
         RS_DBG(dbg_channel, "channel=%ld | %s | ptr(t)=0x%p | isWait=%d | abstime=%d | closed=%d | popWaiting_=%p | pushWaiting_=%p",
             id(), __func__, (void*)&t, isWait, !!abstime, closed_, (void*)popWaiting_, (void*)pushWaiting_);
 
-        if (closed_)
-            return false;
-
-        if (popWaiting_) {   // 有pop协程在等待, 写入 & 清理
+        if (popWaiting_ && popWaiting_ != (ConditionVariable*)kClosedWaiting) {   // 有pop协程在等待, 写入 & 清理
             *popQ_ = t;
             popQ_ = nullptr;
 
@@ -150,6 +152,9 @@ class ChannelImplWithSignal : public DebuggerId<ChannelImplWithSignal<int>>
             return true;
         }
 
+        if (closed_)
+            return false;
+
         if (!isWait) {
             RS_DBG(dbg_channel, "channel=%ld | %s | not match && not wait | return false",
                 id(), __func__);
@@ -166,18 +171,20 @@ class ChannelImplWithSignal : public DebuggerId<ChannelImplWithSignal<int>>
             id(), __func__);
 
         (void)waiting.wait_until_p(lock, abstime, [&]{ return pushWaiting_ != &waiting; });
-        bool ok = pushWaiting_ != &waiting;
+        bool changed = (pushWaiting_ != &waiting);
+        bool ok = changed && pushWaiting_ != (ConditionVariable*)kClosedWaiting;
 
-        RS_DBG(dbg_channel, "channel=%ld | %s | waked | matched=%d",
-            id(), __func__, ok);
+        RS_DBG(dbg_channel, "channel=%ld | %s | waked | closed=%d | changed=%d | ok=%d",
+            id(), __func__, closed_, changed, ok);
 
         if (ok) {
             // 成功
-        } else {
+        } else if (!changed) {
             // 超时，清理
             pushQ_ = nullptr;
             pushWaiting_ = nullptr;
         }
+
         return ok;
     }
 
@@ -194,6 +201,9 @@ class ChannelImplWithSignal : public DebuggerId<ChannelImplWithSignal<int>>
             return push_impl_with_signal_noqueued(t, isWait, abstime, lock);
         }
 
+        if (closed_)
+            return false;
+
         if (!isWait) {
             RS_DBG(dbg_channel, "channel=%ld | %s | push contended && not wait | return false",
                 id(), __func__);
@@ -213,11 +223,36 @@ class ChannelImplWithSignal : public DebuggerId<ChannelImplWithSignal<int>>
             }
         }
 
-        RS_DBG(dbg_channel, "channel=%ld | %s | waked | push idle",
-            id(), __func__);
+        RS_DBG(dbg_channel, "channel=%ld | %s | waked | closed=%d | push idle",
+            id(), __func__, closed_);
+
+        if (closed_)
+            return false;
+
         return push_impl_with_signal_noqueued(t, isWait, abstime, lock);
     }
 
+    void impl_with_signal_close(std::unique_lock<Mutex> & lock)
+    {
+        long push_wakeup = 0;
+        long pop_wakeup = 0;
+        pushQ_ = nullptr;
+        popQ_ = nullptr;
+        if (pushWaiting_) {
+            pushWaiting_->fast_notify_all(lock);
+            pushWaiting_ = (ConditionVariable*)kClosedWaiting;
+            push_wakeup = 1;
+        }
+        if (popWaiting_) {
+            popWaiting_->fast_notify_all(lock);
+            popWaiting_ = (ConditionVariable*)kClosedWaiting;
+            pop_wakeup = 1;
+        }
+
+        RS_DBG(dbg_channel, "channel(...)=%ld | %s | no-cap branch | push-wakeup=%ld | pop-wakeup=%ld",
+                id(), __func__, push_wakeup, pop_wakeup);
+    }
+
 protected:
     Mutex mtx_;
     ConditionVariable pushCv_;
@@ -228,6 +263,8 @@ class ChannelImplWithSignal : public DebuggerId<ChannelImplWithSignal<int>>
     T* popQ_ {nullptr};
     ConditionVariable* pushWaiting_ {nullptr};
     ConditionVariable* popWaiting_ {nullptr};
+
+    static const std::size_t kClosedWaiting = (std::size_t)-1;
 };
 
 template <
@@ -248,6 +285,7 @@ class ChannelImpl : public ChannelImplWithSignal<T>
     using ChannelImplWithSignal<T>::pop_impl_with_signal;
     using ChannelImplWithSignal<T>::push_impl_with_signal;
     using ChannelImplWithSignal<T>::id;
+    using ChannelImplWithSignal<T>::impl_with_signal_close;
 
     explicit ChannelImpl(std::size_t capacity = 0)
         : cap_(capacity)
@@ -302,22 +340,16 @@ class ChannelImpl : public ChannelImplWithSignal<T>
         std::unique_lock<Mutex> lock(mtx_);
         closed_ = true;
         if (!cap_) {
-            pushQ_ = nullptr;
-            popQ_ = nullptr;
-            if (pushWaiting_) {
-                pushWaiting_->fast_notify_all(lock);
-                pushWaiting_ = nullptr;
-            }
-            if (popWaiting_) {
-                popWaiting_->fast_notify_all(lock);
-                popWaiting_ = nullptr;
-            }
+            impl_with_signal_close(lock);
         }
 
-        pushCv_.fast_notify_all(lock);
-        popCv_.fast_notify_all(lock);
-        QueueT q;
-        std::swap(q, q_);
+        long push_wakeup = pushCv_.fast_notify_all(lock);
+        long pop_wakeup = popCv_.fast_notify_all(lock);
+        (void)push_wakeup;
+        (void)pop_wakeup;
+
+        RS_DBG(dbg_channel, "channel(queue)=%ld | %s | cap=%lu | size=%lu | push-wakeup=%ld | pop-wakeup=%ld",
+            id(), __func__, cap_, q_.size(), push_wakeup, pop_wakeup);
     }
 
 private:
@@ -349,7 +381,7 @@ class ChannelImpl : public ChannelImplWithSignal<T>
             return false;
         }
 
-        auto p = [this]{ return q_.size() < cap_; };
+        auto p = [this]{ return q_.size() < cap_ || closed_; };
 
         RS_DBG(dbg_channel, "channel(queue)=%ld | %s | begin wait",
                 id(), __func__);
@@ -404,7 +436,7 @@ class ChannelImpl : public ChannelImplWithSignal<T>
             return false;
         }
 
-        auto p = [this]{ return !q_.empty(); };
+        auto p = [this]{ return !q_.empty() || closed_; };
 
         RS_DBG(dbg_channel, "channel(queue)=%ld | %s | begin wait",
                 id(), __func__);
@@ -418,7 +450,7 @@ class ChannelImpl : public ChannelImplWithSignal<T>
         if (status == std::cv_status::timeout)
             return false;
 
-        if (closed_)
+        if (q_.empty())
             return false;
 
         t = q_.front();
@@ -454,6 +486,7 @@ class ChannelImpl<nullptr_t, QueueT> : public ChannelImplWithSignal<nullptr_t>
     using ChannelImplWithSignal<nullptr_t>::pop_impl_with_signal;
     using ChannelImplWithSignal<nullptr_t>::push_impl_with_signal;
     using ChannelImplWithSignal<nullptr_t>::id;
+    using ChannelImplWithSignal<nullptr_t>::impl_with_signal_close;
 
     explicit ChannelImpl(std::size_t capacity = 0)
         : cap_(capacity), count_(0)
@@ -508,21 +541,16 @@ class ChannelImpl<nullptr_t, QueueT> : public ChannelImplWithSignal<nullptr_t>
         std::unique_lock<Mutex> lock(mtx_);
         closed_ = true;
         if (!cap_) {
-            pushQ_ = nullptr;
-            popQ_ = nullptr;
-            if (pushWaiting_) {
-                pushWaiting_->fast_notify_all(lock);
-                pushWaiting_ = nullptr;
-            }
-            if (popWaiting_) {
-                popWaiting_->fast_notify_all(lock);
-                popWaiting_ = nullptr;
-            }
+            impl_with_signal_close(lock);
         }
 
-        pushCv_.fast_notify_all(lock);
-        popCv_.fast_notify_all(lock);
-        count_ = 0;
+        long push_wakeup = pushCv_.fast_notify_all(lock);
+        long pop_wakeup = popCv_.fast_notify_all(lock);
+        (void)push_wakeup;
+        (void)pop_wakeup;
+
+        RS_DBG(dbg_channel, "channel(void)=%ld | %s | cap=%lu | size=%lu | push-wakeup=%ld | pop-wakeup=%ld",
+            id(), __func__, cap_, count_, push_wakeup, pop_wakeup);
     }
 
 private:
@@ -554,7 +582,7 @@ class ChannelImpl<nullptr_t, QueueT> : public ChannelImplWithSignal<nullptr_t>
             return false;
         }
 
-        auto p = [this]{ return count_ < cap_; };
+        auto p = [this]{ return count_ < cap_ || closed_; };
 
         RS_DBG(dbg_channel, "channel(void)=%ld | %s | begin wait",
                 id(), __func__);
@@ -607,7 +635,7 @@ class ChannelImpl<nullptr_t, QueueT> : public ChannelImplWithSignal<nullptr_t>
             return false;
         }
 
-        auto p = [this]{ return count_ > 0; };
+        auto p = [this]{ return count_ > 0 || closed_; };
 
         RS_DBG(dbg_channel, "channel(void)=%ld | %s | begin wait",
                 id(), __func__);
@@ -621,7 +649,7 @@ class ChannelImpl<nullptr_t, QueueT> : public ChannelImplWithSignal<nullptr_t>
         if (status == std::cv_status::timeout)
             return false;
 
-        if (closed_)
+        if (count_ <= 0)
             return false;
 
         --count_;