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Bug 1471025: Part 1 - Store preference access counts in a separate hashtable. r=njn

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Once the majority of preferences are stored in a read-only shared map, it
won't be possible to modify the access counts in their entries. Which means we
need a separate map for the access counts.

Fortunately, this code is only active in debug builds, so it shouldn't affect
release users. And the net impact on memory usage of this patchset will still
be decidedly downward.

MozReview-Commit-ID: EuLXlMQJP1M
This commit is contained in:
Kris Maglione
2018-07-02 23:33:28 -07:00
parent de3ec69fbe
commit df340082b7
3 changed files with 61 additions and 21 deletions
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70
modules/libpref/Preferences.cpp
View File

@@ -967,10 +967,6 @@ private:
class PrefEntry : public PLDHashEntryHdr
{
public:
#ifdef DEBUG
// This field is before mPref to minimize sizeof(PrefEntry) on 64-bit.
uint32_t mAccessCount;
#endif
Pref* mPref; // Note: this is never null in a live entry.
static bool MatchEntry(const PLDHashEntryHdr* aEntry, const void* aKey)
@@ -986,9 +982,6 @@ public:
auto entry = static_cast<PrefEntry*>(aEntry);
auto prefName = static_cast<const char*>(aKey);
#ifdef DEBUG
entry->mAccessCount = 0;
#endif
entry->mPref = new Pref(prefName);
}
@@ -1076,6 +1069,43 @@ static PLDHashTable* gHashTable;
static CallbackNode* gFirstCallback = nullptr;
static CallbackNode* gLastPriorityNode = nullptr;
#ifdef DEBUG
#define ACCESS_COUNTS
#endif
#ifdef ACCESS_COUNTS
using AccessCountsHashTable = nsDataHashtable<nsCStringHashKey, uint32_t>;
static AccessCountsHashTable* gAccessCounts;
static void
AddAccessCount(const nsACString& aPrefName)
{
// FIXME: Servo reads preferences from background threads in unsafe ways (bug
// 1474789), and triggers assertions here if we try to add usage count entries
// from background threads.
if (NS_IsMainThread()) {
uint32_t& count = gAccessCounts->GetOrInsert(aPrefName);
count++;
}
}
static void
AddAccessCount(const char* aPrefName)
{
AddAccessCount(nsDependentCString(aPrefName));
}
#else
static void MOZ_MAYBE_UNUSED
AddAccessCount(const nsACString& aPrefName)
{
}
static void
AddAccessCount(const char* aPrefName)
{
}
#endif
// These are only used during the call to NotifyCallbacks().
static bool gCallbacksInProgress = false;
static bool gShouldCleanupDeadNodes = false;
@@ -1147,9 +1177,7 @@ pref_HashTableLookup(const char* aPrefName)
return nullptr;
}
#ifdef DEBUG
entry->mAccessCount += 1;
#endif
AddAccessCount(aPrefName);
return entry->mPref;
}
@@ -3275,6 +3303,11 @@ Preferences::GetInstanceForService()
gTelemetryLoadData =
new nsDataHashtable<nsCStringHashKey, TelemetryLoadData>();
#ifdef ACCESS_COUNTS
MOZ_ASSERT(!gAccessCounts);
gAccessCounts = new AccessCountsHashTable();
#endif
gCacheData = new nsTArray<nsAutoPtr<CacheData>>();
gCacheDataDesc = "set by GetInstanceForService() (1)";
@@ -3408,6 +3441,10 @@ Preferences::~Preferences()
delete gTelemetryLoadData;
gTelemetryLoadData = nullptr;
#ifdef ACCESS_COUNTS
delete gAccessCounts;
#endif
gPrefNameArena.Clear();
}
@@ -3744,10 +3781,9 @@ Preferences::GetDefaultBranch(const char* aPrefRoot, nsIPrefBranch** aRetVal)
NS_IMETHODIMP
Preferences::ReadStats(nsIPrefStatsCallback* aCallback)
{
#ifdef DEBUG
for (auto iter = gHashTable->Iter(); !iter.Done(); iter.Next()) {
PrefEntry* entry = static_cast<PrefEntry*>(iter.Get());
aCallback->Visit(entry->mPref->Name(), entry->mAccessCount);
#ifdef ACCESS_COUNTS
for (auto iter = gAccessCounts->Iter(); !iter.Done(); iter.Next()) {
aCallback->Visit(iter.Key(), iter.Data());
}
return NS_OK;
@@ -3759,10 +3795,8 @@ Preferences::ReadStats(nsIPrefStatsCallback* aCallback)
NS_IMETHODIMP
Preferences::ResetStats()
{
#ifdef DEBUG
for (auto iter = gHashTable->Iter(); !iter.Done(); iter.Next()) {
static_cast<PrefEntry*>(iter.Get())->mAccessCount = 0;
}
#ifdef ACCESS_COUNTS
gAccessCounts->Clear();
return NS_OK;
#else
return NS_ERROR_NOT_IMPLEMENTED;