From de8fceb34dae6f99fe06c0be0b0c9fe9dfa12272 Mon Sep 17 00:00:00 2001
From: Nicholas Nethercote <nnethercote@mozilla.com>
Date: Mon, 7 Sep 2015 19:20:12 -0700
Subject: [PATCH] Bug 1202526 (part 1) - Add PLDHashTable::RemoveEntry().
 r=froydnj.

This patch also consolidates the shrink handling so it's now entirely within
ShrinkIfAppropriate().
---
 xpcom/glue/pldhash.cpp | 22 +++++++++++++---------
 xpcom/glue/pldhash.h   | 13 ++++++++++++-
 2 files changed, 25 insertions(+), 10 deletions(-)

diff --git a/xpcom/glue/pldhash.cpp b/xpcom/glue/pldhash.cpp
index 8f0333ced47d..22781ce9c942 100644
--- a/xpcom/glue/pldhash.cpp
+++ b/xpcom/glue/pldhash.cpp
@@ -662,18 +662,22 @@ PLDHashTable::Remove(const void* aKey)
                                                           ComputeKeyHash(aKey))
                          : nullptr;
   if (entry) {
-    // Clear this entry and mark it as "removed".
     RawRemove(entry);
-
-    // Shrink if alpha is <= .25 and the table isn't too small already.
-    uint32_t capacity = Capacity();
-    if (capacity > kMinCapacity &&
-        mEntryCount <= MinLoad(capacity)) {
-      (void) ChangeTable(-1);
-    }
+    ShrinkIfAppropriate();
   }
 }
 
+void
+PLDHashTable::RemoveEntry(PLDHashEntryHdr* aEntry)
+{
+#ifdef DEBUG
+  AutoWriteOp op(mChecker);
+#endif
+
+  RawRemove(aEntry);
+  ShrinkIfAppropriate();
+}
+
 PLDHashEntryHdr* PL_DHASH_FASTCALL
 PL_DHashTableSearch(PLDHashTable* aTable, const void* aKey)
 {
@@ -709,7 +713,7 @@ PLDHashTable::RawRemove(PLDHashEntryHdr* aEntry)
 
   MOZ_ASSERT(mEntryStore.Get());
 
-  NS_ASSERTION(EntryIsLive(aEntry), "EntryIsLive(aEntry)");
+  MOZ_ASSERT(EntryIsLive(aEntry), "EntryIsLive(aEntry)");
 
   // Load keyHash first in case clearEntry() goofs it.
   PLDHashNumber keyHash = aEntry->mKeyHash;
diff --git a/xpcom/glue/pldhash.h b/xpcom/glue/pldhash.h
index e77e623d1bf1..4d330baec227 100644
--- a/xpcom/glue/pldhash.h
+++ b/xpcom/glue/pldhash.h
@@ -350,12 +350,23 @@ public:
   //   table.Remove(key);
   //
   // If |key|'s entry is found, it is cleared (via table->mOps->clearEntry).
+  // The table's capacity may be reduced afterwards.
   void Remove(const void* aKey);
 
+  // To remove an entry found by a prior search, call:
+  //
+  //   table.RemoveEntry(entry);
+  //
+  // The entry, which must be present and in use, is cleared (via
+  // table->mOps->clearEntry). The table's capacity may be reduced afterwards.
+  void RemoveEntry(PLDHashEntryHdr* aEntry);
+
   // Remove an entry already accessed via Search() or Add().
   //
   // NB: this is a "raw" or low-level method. It does not shrink the table if
-  // it is underloaded. Don't use it unless you know what you are doing.
+  // it is underloaded. Don't use it unless necessary and you know what you are
+  // doing, and if so, please explain in a comment why it is necessary instead
+  // of RemoveEntry().
   void RawRemove(PLDHashEntryHdr* aEntry);
 
   // This function is equivalent to