From e52397fb6365776a7f404edc0a06c9e94cfb307a Mon Sep 17 00:00:00 2001
From: Michael Davidsaver <mdavidsaver@gmail.com>
Date: Tue, 28 Jul 2020 09:21:07 -0700
Subject: [PATCH] Operation::cancel() return true if cancelled

---
 src/clientget.cpp        | 12 ++++++++----
 src/clientintrospect.cpp | 12 ++++++++----
 src/clientmon.cpp        | 12 ++++++++----
 src/pvxs/client.h        |  5 +++--
 4 files changed, 27 insertions(+), 14 deletions(-)

diff --git a/src/clientget.cpp b/src/clientget.cpp
index eb6b864..51d9438 100644
--- a/src/clientget.cpp
+++ b/src/clientget.cpp
@@ -162,19 +162,21 @@ struct GPROp : public OperationBase
         }
     }
 
-    virtual void cancel() override final
+    virtual bool cancel() override final
     {
         auto context = chan->context;
         decltype (done) junk;
-        context->tcp_loop.call([this, &junk](){
-            _cancel(false);
+        bool ret;
+        context->tcp_loop.call([this, &junk, &ret](){
+            ret = _cancel(false);
             junk = std::move(done);
             // leave opByIOID for GC
         });
+        return ret;
     }
 
 
-    void _cancel(bool implicit) {
+    bool _cancel(bool implicit) {
         if(implicit && state!=Done) {
             log_warn_printf(setup, "implied cancel of op%x on channel '%s'\n",
                             op, chan ? chan->name.c_str() : "");
@@ -186,7 +188,9 @@ struct GPROp : public OperationBase
             chan->conn->opByIOID.erase(ioid);
             chan->opByIOID.erase(ioid);
         }
+        bool ret = state!=Done;
         state = Done;
+        return ret;
     }
 
     virtual void createOp() override final
diff --git a/src/clientintrospect.cpp b/src/clientintrospect.cpp
index 8c43007..0e30179 100644
--- a/src/clientintrospect.cpp
+++ b/src/clientintrospect.cpp
@@ -40,17 +40,19 @@ struct InfoOp : public OperationBase
         _cancel(true);
     }
 
-    virtual void cancel() override final {
+    virtual bool cancel() override final {
         auto context = chan->context;
         decltype (done) junk;
-        context->tcp_loop.call([this, &junk](){
-            _cancel(false);
+        bool ret = false;
+        context->tcp_loop.call([this, &junk, &ret](){
+            ret = _cancel(false);
             junk = std::move(done);
             // leave opByIOID for GC
         });
+        return ret;
     }
 
-    void _cancel(bool implicit) {
+    bool _cancel(bool implicit) {
         if(implicit && state!=Done) {
             log_warn_printf(setup, "implied cancel of INFO on channel '%s'\n",
                             chan ? chan->name.c_str() : "");
@@ -62,7 +64,9 @@ struct InfoOp : public OperationBase
             chan->conn->opByIOID.erase(ioid);
             chan->opByIOID.erase(ioid);
         }
+        bool ret = state!=Done;
         state = Done;
+        return ret;
     }
 
     virtual void createOp() override final
diff --git a/src/clientmon.cpp b/src/clientmon.cpp
index da86d85..0096ae6 100644
--- a/src/clientmon.cpp
+++ b/src/clientmon.cpp
@@ -162,17 +162,19 @@ struct SubscriptionImpl : public OperationBase, public Subscription
         return ret;
     }
 
-    virtual void cancel() override final {
+    virtual bool cancel() override final {
         auto context = chan->context;
         decltype (event) junk;
-        context->tcp_loop.call([this, &junk](){
-            _cancel(false);
+        bool ret;
+        context->tcp_loop.call([this, &junk, &ret](){
+            ret = _cancel(false);
             junk = std::move(event);
             // leave opByIOID for GC
         });
+        return ret;
     }
 
-    void _cancel(bool implicit) {
+    bool _cancel(bool implicit) {
         if(implicit && state!=Done) {
             log_info_printf(io, "Server %s channel %s monitor implied cancel\n",
                             chan->conn ? chan->conn->peerName.c_str() : "<disconnected>",
@@ -192,7 +194,9 @@ struct SubscriptionImpl : public OperationBase, public Subscription
             if(pipeline)
                 (void)event_del(ackTick.get());
         }
+        bool ret = state!=Done;
         state = Done;
+        return ret;
     }
 
     virtual void createOp() override final
diff --git a/src/pvxs/client.h b/src/pvxs/client.h
index b23496f..2c4b165 100644
--- a/src/pvxs/client.h
+++ b/src/pvxs/client.h
@@ -117,7 +117,8 @@ struct PVXS_API Operation {
 
     //! Explicitly cancel a pending operation.
     //! Blocks until an in-progress callback has completed.
-    virtual void cancel() =0;
+    //! @returns true if the operation was cancelled, or false if already complete.
+    virtual bool cancel() =0;
 
     /** @brief Block until Operation completion
      *
@@ -147,7 +148,7 @@ struct PVXS_API Subscription {
 
     //! Explicitly cancel a active subscription.
     //! Blocks until any in-progress callback has completed.
-    virtual void cancel() =0;
+    virtual bool cancel() =0;
 
     //! Ask a server to stop sending updates to this Subscription
     virtual void pause(bool p=true) =0;