From: Alex Rousskov <rousskov@measurement-factory.com>
Date: Tue, 25 Jun 2013 19:19:28 +0000 (-0600)
Subject: Do not broadcast changes if there are no remote readers.
X-Git-Tag: SQUID_3_5_0_1~444^2~46
X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=d366a7fab6835a63ad6917f661251878b56ce47b;p=thirdparty%2Fsquid.git

Do not broadcast changes if there are no remote readers.

New/future readers should anchor themselves to the cache in order to get the
earlier updates they missed.
---

diff --git a/src/CollapsedForwarding.cc b/src/CollapsedForwarding.cc
index 629327d546..345f1b340f 100644
--- a/src/CollapsedForwarding.cc
+++ b/src/CollapsedForwarding.cc
@@ -8,6 +8,7 @@
 #include "ipc/Messages.h"
 #include "ipc/Port.h"
 #include "ipc/TypedMsgHdr.h"
+#include "MemObject.h"
 #include "CollapsedForwarding.h"
 #include "globals.h"
 #include "SquidConfig.h"
@@ -50,6 +51,12 @@ CollapsedForwarding::Broadcast(const StoreEntry &e)
     if (!queue.get())
         return;
 
+    if (!e.mem_obj || e.mem_obj->xitTable.index < 0 ||
+        !Store::Root().transientReaders(e)) {
+        debugs(17, 7, "not broadcasting " << e << " changes to nobody");
+        return;
+    }
+
     CollapsedForwardingMsg msg;
     msg.sender = KidIdentifier;
     memcpy(msg.key, e.key, sizeof(msg.key));
diff --git a/src/Store.h b/src/Store.h
index d2131fe388..e689680f3d 100644
--- a/src/Store.h
+++ b/src/Store.h
@@ -392,6 +392,11 @@ public:
     /// calls Root().transients->abandon() if transients are tracked
     virtual void transientsAbandon(StoreEntry &e) {}
 
+    // XXX: This method belongs to Store::Root/StoreController, but it is here
+    // to avoid casting Root() to StoreController until Root() API is fixed.
+    /// number of the transient entry readers some time ago
+    virtual int transientReaders(const StoreEntry &e) const { return 0; }
+
     // XXX: This method belongs to Store::Root/StoreController, but it is here
     // to avoid casting Root() to StoreController until Root() API is fixed.
     /// disassociates the entry from the intransit table
diff --git a/src/SwapDir.h b/src/SwapDir.h
index fc2ed8f749..68fe0beeb2 100644
--- a/src/SwapDir.h
+++ b/src/SwapDir.h
@@ -64,6 +64,7 @@ public:
     virtual void handleIdleEntry(StoreEntry &e);
     virtual void transientsCompleteWriting(StoreEntry &e);
     virtual void transientsAbandon(StoreEntry &e);
+    virtual int transientReaders(const StoreEntry &e) const;
     virtual void transientsDisconnect(MemObject &mem_obj);
     virtual void memoryOut(StoreEntry &e, const bool preserveSwappable);
     virtual void memoryUnlink(StoreEntry &e);
diff --git a/src/Transients.cc b/src/Transients.cc
index 340f2ee599..c6967b8409 100644
--- a/src/Transients.cc
+++ b/src/Transients.cc
@@ -306,6 +306,16 @@ Transients::completeWriting(const StoreEntry &e)
     }
 }
 
+int
+Transients::readers(const StoreEntry &e) const
+{
+    if (e.mem_obj && e.mem_obj->xitTable.index >= 0) {
+        assert(map);
+        return map->peekAtEntry(e.mem_obj->xitTable.index).lock.readers;
+    }
+    return 0;
+}
+
 void
 Transients::disconnect(MemObject &mem_obj)
 {
diff --git a/src/Transients.h b/src/Transients.h
index 12d784d2b5..cbe2138f6c 100644
--- a/src/Transients.h
+++ b/src/Transients.h
@@ -36,6 +36,9 @@ public:
     /// whether an in-transit entry is now abandoned by its writer
     bool abandoned(const StoreEntry &e) const;
 
+    /// number of entry readers some time ago
+    int readers(const StoreEntry &e) const;
+
     /// the caller is done writing or reading this entry
     void disconnect(MemObject &mem_obj);
 
diff --git a/src/ipc/StoreMap.cc b/src/ipc/StoreMap.cc
index 7c602fb1c7..db26250d0f 100644
--- a/src/ipc/StoreMap.cc
+++ b/src/ipc/StoreMap.cc
@@ -212,6 +212,13 @@ Ipc::StoreMap::peekAtReader(const sfileno fileno) const
     return NULL;
 }
 
+const Ipc::StoreMap::Anchor &
+Ipc::StoreMap::peekAtEntry(const sfileno fileno) const
+{
+    assert(valid(fileno));
+    return shared->slots[fileno].anchor;
+}
+
 void
 Ipc::StoreMap::freeEntry(const sfileno fileno)
 {
diff --git a/src/ipc/StoreMap.h b/src/ipc/StoreMap.h
index ddcf88afb9..c1edb2378b 100644
--- a/src/ipc/StoreMap.h
+++ b/src/ipc/StoreMap.h
@@ -152,6 +152,9 @@ public:
     /// only works on locked entries; returns nil unless the slice is readable
     const Anchor *peekAtReader(const sfileno fileno) const;
 
+    /// only works on locked entries; returns the corresponding Anchor
+    const Anchor &peekAtEntry(const sfileno fileno) const;
+
     /// free the entry if possible or mark it as waiting to be freed if not
     void freeEntry(const sfileno fileno);
     /// free the entry if possible or mark it as waiting to be freed if not
diff --git a/src/store_dir.cc b/src/store_dir.cc
index f1197c2ca3..6584f360dc 100644
--- a/src/store_dir.cc
+++ b/src/store_dir.cc
@@ -918,6 +918,13 @@ StoreController::transientsCompleteWriting(StoreEntry &e)
     }
 }
 
+int
+StoreController::transientReaders(const StoreEntry &e) const
+{
+    return (transients && e.mem_obj && e.mem_obj->xitTable.index >= 0) ?
+        transients->readers(e) : 0;
+}
+
 void
 StoreController::transientsDisconnect(MemObject &mem_obj)
 {