Refactor the context and entry to support asynchronous invocation chain

Signed-off-by: Eric Zhao <sczyh16@gmail.com>

sentinel-core/src/main/java/com/alibaba/csp/sentinel/AsyncEntry.java

@@ -0,0 +1,84 @@
+/*
+ * Copyright 1999-2018 Alibaba Group Holding Ltd.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package com.alibaba.csp.sentinel;
+
+import com.alibaba.csp.sentinel.context.Context;
+import com.alibaba.csp.sentinel.slotchain.ProcessorSlot;
+import com.alibaba.csp.sentinel.slotchain.ResourceWrapper;
+
+/**
+ * The entry for asynchronous resources.
+ *
+ * @author Eric Zhao
+ * @since 0.2.0
+ */
+public class AsyncEntry extends CtEntry {
+
+    private Context asyncContext;
+
+    AsyncEntry(ResourceWrapper resourceWrapper, ProcessorSlot<Object> chain, Context context) {
+        super(resourceWrapper, chain, context);
+    }
+
+    /**
+     * Remove current entry from local context, but does not exit.
+     */
+    void cleanCurrentEntryInLocal() {
+        Context originalContext = context;
+        if (originalContext != null) {
+            Entry curEntry = originalContext.getCurEntry();
+            if (curEntry == this) {
+                Entry parent = this.parent;
+                originalContext.setCurEntry(parent);
+                if (parent != null) {
+                    ((CtEntry)parent).child = null;
+                }
+            } else {
+                throw new IllegalStateException("Bad async context state");
+            }
+        }
+    }
+
+    public Context getAsyncContext() {
+        return asyncContext;
+    }
+
+    /**
+     * The async context should not be initialized until the node for current resource has been set to current entry.
+     */
+    void initAsyncContext() {
+        if (asyncContext == null) {
+            this.asyncContext = Context.newAsyncContext(context.getEntranceNode(), context.getName())
+                .setOrigin(context.getOrigin())
+                .setCurEntry(this);
+        } else {
+            throw new IllegalStateException("Duplicate initialize of async context");
+        }
+    }
+
+    @Override
+    protected void clearEntryContext() {
+        super.clearEntryContext();
+        this.asyncContext = null;
+    }
+
+    @Override
+    protected Entry trueExit(int count, Object... args) throws ErrorEntryFreeException {
+        exitForContext(asyncContext, count, args);
+
+        return parent;
+    }
+}

sentinel-core/src/main/java/com/alibaba/csp/sentinel/CtEntry.java

@@ -0,0 +1,103 @@
+/*
+ * Copyright 1999-2018 Alibaba Group Holding Ltd.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package com.alibaba.csp.sentinel;
+
+import com.alibaba.csp.sentinel.context.Context;
+import com.alibaba.csp.sentinel.context.ContextUtil;
+import com.alibaba.csp.sentinel.node.Node;
+import com.alibaba.csp.sentinel.slotchain.ProcessorSlot;
+import com.alibaba.csp.sentinel.slotchain.ResourceWrapper;
+
+/**
+ * Linked entry within current context.
+ *
+ * @author jialiang.linjl
+ * @author Eric Zhao
+ */
+class CtEntry extends Entry {
+
+    protected Entry parent = null;
+    protected Entry child = null;
+
+    protected ProcessorSlot<Object> chain;
+    protected Context context;
+
+    CtEntry(ResourceWrapper resourceWrapper, ProcessorSlot<Object> chain, Context context) {
+        super(resourceWrapper);
+        this.chain = chain;
+        this.context = context;
+
+        setUpEntryFor(context);
+    }
+
+    private void setUpEntryFor(Context context) {
+        this.parent = context.getCurEntry();
+        if (parent != null) {
+            ((CtEntry)parent).child = this;
+        }
+        context.setCurEntry(this);
+    }
+
+    @Override
+    public void exit(int count, Object... args) throws ErrorEntryFreeException {
+        trueExit(count, args);
+    }
+
+    protected void exitForContext(Context context, int count, Object... args) throws ErrorEntryFreeException {
+        if (context != null) {
+            if (context.getCurEntry() != this) {
+                // Clean previous call stack.
+                CtEntry e = (CtEntry)context.getCurEntry();
+                while (e != null) {
+                    e.exit(count, args);
+                    e = (CtEntry)e.parent;
+                }
+                throw new ErrorEntryFreeException("The order of entry free is can't be paired with the order of entry");
+            } else {
+                if (chain != null) {
+                    chain.exit(context, resourceWrapper, count, args);
+                }
+                // Restore the call stack.
+                context.setCurEntry(parent);
+                if (parent != null) {
+                    ((CtEntry)parent).child = null;
+                }
+                if (parent == null) {
+                    // Auto-created entry indicates immediate exit.
+                    ContextUtil.exit();
+                }
+                // Clean the reference of context in current entry to avoid duplicate exit.
+                clearEntryContext();
+            }
+        }
+    }
+
+    protected void clearEntryContext() {
+        this.context = null;
+    }
+
+    @Override
+    protected Entry trueExit(int count, Object... args) throws ErrorEntryFreeException {
+        exitForContext(context, count, args);
+
+        return parent;
+    }
+
+    @Override
+    public Node getLastNode() {
+        return parent == null ? null : parent.getCurNode();
+    }
+}

sentinel-core/src/main/java/com/alibaba/csp/sentinel/CtSph.java

@@ -23,7 +23,6 @@ import com.alibaba.csp.sentinel.log.RecordLog;
 import com.alibaba.csp.sentinel.context.Context;
 import com.alibaba.csp.sentinel.context.ContextUtil;
 import com.alibaba.csp.sentinel.context.NullContext;
-import com.alibaba.csp.sentinel.node.Node;
 import com.alibaba.csp.sentinel.slotchain.MethodResourceWrapper;
 import com.alibaba.csp.sentinel.slotchain.ProcessorSlot;
 import com.alibaba.csp.sentinel.slotchain.ProcessorSlotChain;
@@ -53,6 +52,46 @@ public class CtSph implements Sph {
 
     private static final Object LOCK = new Object();
 
+    private AsyncEntry asyncEntryInternal(ResourceWrapper resourceWrapper, int count, Object... args) throws BlockException {
+        Context context = ContextUtil.getContext();
+        if (context instanceof NullContext) {
+            // Init the entry only. No rule checking will occur.
+            return new AsyncEntry(resourceWrapper, null, context);
+        }
+        if (context == null) {
+            context = MyContextUtil.myEnter(Constants.CONTEXT_DEFAULT_NAME, "", resourceWrapper.getType());
+        }
+
+        // Global switch is turned off, so no rule checking will be done.
+        if (!Constants.ON) {
+            return new AsyncEntry(resourceWrapper, null, context);
+        }
+
+        ProcessorSlot<Object> chain = lookProcessChain(resourceWrapper);
+
+        // Means processor cache size exceeds {@link Constants.MAX_SLOT_CHAIN_SIZE}, so no rule checking will be done.
+        if (chain == null) {
+            return new AsyncEntry(resourceWrapper, null, context);
+        }
+
+        AsyncEntry asyncEntry = new AsyncEntry(resourceWrapper, chain, context);
+        try {
+            chain.entry(context, resourceWrapper, null, count, args);
+            // Initiate the async context.
+            asyncEntry.initAsyncContext();
+        } catch (BlockException e1) {
+            asyncEntry.exit(count, args);
+            throw e1;
+        } catch (Throwable e1) {
+            RecordLog.info("Sentinel unexpected exception", e1);
+        } finally {
+            // The asynchronous call may take time in background, and current context should not be hanged on it.
+            // So we need to remove current async entry from current context.
+            asyncEntry.cleanCurrentEntryInLocal();
+        }
+        return asyncEntry;
+    }
+
     /**
      * Do all {@link Rule}s checking about the resource.
      *
@@ -145,68 +184,6 @@ public class CtSph implements Sph {
         return chain;
     }
 
-    private static class CtEntry extends Entry {
-
-        protected Entry parent = null;
-        protected Entry child = null;
-        private ProcessorSlot<Object> chain;
-        private Context context;
-
-        CtEntry(ResourceWrapper resourceWrapper, ProcessorSlot<Object> chain, Context context) {
-            super(resourceWrapper);
-            this.chain = chain;
-            this.context = context;
-            parent = context.getCurEntry();
-            if (parent != null) {
-                ((CtEntry)parent).child = this;
-            }
-            context.setCurEntry(this);
-        }
-
-        @Override
-        public void exit(int count, Object... args) throws ErrorEntryFreeException {
-            trueExit(count, args);
-        }
-
-        @Override
-        protected Entry trueExit(int count, Object... args) throws ErrorEntryFreeException {
-            if (context != null) {
-                if (context.getCurEntry() != this) {
-                    // Clean previous call stack.
-                    CtEntry e = (CtEntry)context.getCurEntry();
-                    while (e != null) {
-                        e.exit(count, args);
-                        e = (CtEntry)e.parent;
-                    }
-                    throw new ErrorEntryFreeException(
-                        "The order of entry free is can't be paired with the order of entry");
-                } else {
-                    if (chain != null) {
-                        chain.exit(context, resourceWrapper, count, args);
-                    }
-                    // Modify the call stack.
-                    context.setCurEntry(parent);
-                    if (parent != null) {
-                        ((CtEntry)parent).child = null;
-                    }
-                    if (parent == null) {
-                        // Auto-created entry indicates immediate exit.
-                        ContextUtil.exit();
-                    }
-                    // Clean the reference of context in current entry to avoid duplicate exit.
-                    context = null;
-                }
-            }
-            return parent;
-
-        }
-
-        @Override
-        public Node getLastNode() {
-            return parent == null ? null : parent.getCurNode();
-        }
-    }
-
     /**
      * This class is used for skip context name checking.
      */
@@ -275,4 +252,10 @@ public class CtSph implements Sph {
         StringResourceWrapper resource = new StringResourceWrapper(name, type);
         return entry(resource, count, args);
     }
+
+    @Override
+    public AsyncEntry asyncEntry(String name, EntryType type, int count, Object... args) throws BlockException {
+        StringResourceWrapper resource = new StringResourceWrapper(name, type);
+        return asyncEntryInternal(resource, count, args);
+    }
 }

sentinel-core/src/main/java/com/alibaba/csp/sentinel/Sph.java

@@ -27,6 +27,7 @@ import com.alibaba.csp.sentinel.slots.block.BlockException;
  * @author qinan.qn
  * @author jialiang.linjl
  * @author leyou
+ * @author Eric Zhao
  */
 public interface Sph {
 
@@ -135,11 +136,23 @@ public interface Sph {
      * @param type  the resource is an inbound or an outbound method. This is used
      *              to mark whether it can be blocked when the system is unstable
      * @param count the count that the resource requires
-     * @param args  the parameters of the method. It can also be counted by setting
-     *              hot parameter rule
-     * @return entry get.
+     * @param args  the parameters of the method. It can also be counted by setting hot parameter rule
+     * @return entry get
      * @throws BlockException if the block criteria is met
      */
     Entry entry(String name, EntryType type, int count, Object... args) throws BlockException;
 
+    /**
+     * Create a protected asynchronous resource.
+     *
+     * @param name  the unique name for the protected resource
+     * @param type  the resource is an inbound or an outbound method. This is used
+     *              to mark whether it can be blocked when the system is unstable
+     * @param count the count that the resource requires
+     * @param args  the parameters of the method. It can also be counted by setting hot parameter rule
+     * @return created asynchronous entry
+     * @throws BlockException if the block criteria is met
+     * @since 0.2.0
+     */
+    AsyncEntry asyncEntry(String name, EntryType type, int count, Object... args) throws BlockException;
 }

sentinel-core/src/main/java/com/alibaba/csp/sentinel/SphU.java

@@ -69,6 +69,7 @@ import com.alibaba.csp.sentinel.slots.system.SystemRuleManager;
  * </p>
  *
  * @author jialiang.linjl
+ * @author Eric Zhao
  * @see SphO
  */
 public class SphU {
@@ -200,4 +201,45 @@ public class SphU {
     public static Entry entry(String name, EntryType type, int count, Object... args) throws BlockException {
         return Env.sph.entry(name, type, count, args);
     }
+
+    /**
+     * Checking all rules about the asynchronous resource.
+     *
+     * @param name the unique name of the protected resource
+     * @throws BlockException if the block criteria is met, eg. when any rule's threshold is exceeded
+     * @since 0.2.0
+     */
+    public static AsyncEntry asyncEntry(String name) throws BlockException {
+        return Env.sph.asyncEntry(name, EntryType.OUT, 1, OBJECTS0);
+    }
+
+    /**
+     * Checking all {@link Rule}s about the asynchronous resource.
+     *
+     * @param name the unique name for the protected resource
+     * @param type the resource is an inbound or an outbound method. This is used
+     *             to mark whether it can be blocked when the system is unstable,
+     *             only inbound traffic could be blocked by {@link SystemRule}
+     * @throws BlockException if the block criteria is met, eg. when any rule's threshold is exceeded
+     * @since 0.2.0
+     */
+    public static AsyncEntry asyncEntry(String name, EntryType type) throws BlockException {
+        return Env.sph.asyncEntry(name, type, 1, OBJECTS0);
+    }
+
+    /**
+     * Checking all {@link Rule}s about the asynchronous resource.
+     *
+     * @param name  the unique name for the protected resource
+     * @param type  the resource is an inbound or an outbound method. This is used
+     *              to mark whether it can be blocked when the system is unstable,
+     *              only inbound traffic could be blocked by {@link SystemRule}
+     * @param count tokens required
+     * @param args  extra parameters
+     * @throws BlockException if the block criteria is met, eg. when any rule's threshold is exceeded
+     * @since 0.2.0
+     */
+    public static AsyncEntry asyncEntry(String name, EntryType type, int count, Object... args) throws BlockException {
+        return Env.sph.asyncEntry(name, type, count, args);
+    }
 }

sentinel-core/src/main/java/com/alibaba/csp/sentinel/context/Context.java

@@ -32,8 +32,9 @@ import com.alibaba.csp.sentinel.slots.nodeselector.NodeSelectorSlot;
  * <li>the current {@link Entry}: the current invocation point.</li>
  * <li>the current {@link Node}: the statistics related to the
  * {@link Entry}.</li>
- * <li>the origin:The origin is useful when we want to control different
- * invoker/consumer separately. Usually the origin could be the Service Consumer's app name. </li>
+ * <li>the origin: The origin is useful when we want to control different
+ * invoker/consumer separately. Usually the origin could be the Service Consumer's app name
+ * or origin IP. </li>
  * </ul>
  * <p>
  * Each {@link SphU}#entry() or {@link SphO}#entry() should be in a {@link Context},
@@ -58,7 +59,7 @@ public class Context {
     /**
      * Context name.
      */
-    private String name;
+    private final String name;
 
     /**
      * The entrance node of current invocation tree.
@@ -71,14 +72,36 @@ public class Context {
     private Entry curEntry;
 
     /**
-     * the origin of this context, usually the origin is the Service Consumer's app name.
+     * The origin of this context (usually indicate different invokers, e.g. service consumer name or origin IP).
      */
     private String origin = "";
 
+    private final boolean async;
+
+    /**
+     * Create a new async context.
+     *
+     * @param entranceNode entrance node of the context
+     * @param name context name
+     * @return the new created context
+     * @since 0.2.0
+     */
+    public static Context newAsyncContext(DefaultNode entranceNode, String name) {
+        return new Context(name, entranceNode, true);
+    }
+
     public Context(DefaultNode entranceNode, String name) {
-        super();
+        this(name, entranceNode, false);
+    }
+
+    public Context(String name, DefaultNode entranceNode, boolean async) {
         this.name = name;
         this.entranceNode = entranceNode;
+        this.async = async;
+    }
+
+    public boolean isAsync() {
+        return async;
     }
 
     public String getName() {
@@ -89,24 +112,27 @@ public class Context {
         return curEntry.getCurNode();
     }
 
-    public void setCurNode(Node node) {
+    public Context setCurNode(Node node) {
         this.curEntry.setCurNode(node);
+        return this;
     }
 
     public Entry getCurEntry() {
         return curEntry;
     }
 
-    public void setCurEntry(Entry curEntry) {
+    public Context setCurEntry(Entry curEntry) {
         this.curEntry = curEntry;
+        return this;
     }
 
     public String getOrigin() {
         return origin;
     }
 
-    public void setOrigin(String origin) {
+    public Context setOrigin(String origin) {
         this.origin = origin;
+        return this;
     }
 
     public double getOriginTotalQps() {

sentinel-core/src/main/java/com/alibaba/csp/sentinel/context/ContextUtil.java

@@ -175,4 +175,45 @@ public class ContextUtil {
     public static Context getContext() {
         return contextHolder.get();
     }
+
+    /**
+     * <p>
+     * Replace current context with the provided context.
+     * This is mainly designed for context switching (e.g. in asynchronous invocation).
+     * </p>
+     * <p>
+     * Note: When switching context manually, remember to restore the original context.
+     * For common scenarios, you can use {@link #runOnContext(Context, Runnable)}.
+     * </p>
+     *
+     * @param newContext new context to set
+     * @return old context
+     * @since 0.2.0
+     */
+    private static Context replaceContext(Context newContext) {
+        Context backupContext = contextHolder.get();
+        if (newContext == null) {
+            contextHolder.remove();
+        } else {
+            contextHolder.set(newContext);
+        }
+        return backupContext;
+    }
+
+    /**
+     * Execute the code within provided context.
+     * This is mainly designed for context switching (e.g. in asynchronous invocation).
+     *
+     * @param context the context
+     * @param f       lambda to run within the context
+     * @since 0.2.0
+     */
+    public static void runOnContext(Context context, Runnable f) {
+        Context curContext = replaceContext(context);
+        try {
+            f.run();
+        } finally {
+            replaceContext(curContext);
+        }
+    }
 }