Skip to content

Replace MemoryBarrier with Volatile operations in HashMap #125259

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Merged
AaronRobinsonMSFT merged 1 commit into from
Mar 7, 2026
+29 −35
Merged

Replace MemoryBarrier with Volatile operations in HashMap #125259

Changes from all commits
Commits
Show all changes
1 commit
Select commit
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
64 changes: 29 additions & 35 deletions src/coreclr/vm/hash.cpp
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -77,13 +77,10 @@ BOOL Bucket::InsertValue(const UPTR key, const UPTR value)
{
SetValue (value, i);

// On multiprocessors we should make sure that
// the value is propagated before we proceed.
// inline memory barrier call, refer to
// function description at the beginning of this
MemoryBarrier();

m_rgKeys[i] = key;
// Release store: ensures the value is visible before the
// key that publishes it. Pairs with the acquire load in
// LookupValue/ReplaceValue/DeleteValue.
VolatileStore(&m_rgKeys[i], key);
return true;
}
} // for i= 0; i < SLOTS_PER_BUCKET; loop
Expand Down Expand Up @@ -590,13 +587,11 @@ UPTR HashMap::LookupValue(UPTR key, UPTR value)
PTR_Bucket pBucket = rgBuckets+(seed % cbSize);
for (unsigned int i = 0; i < SLOTS_PER_BUCKET; i++)
{
if (pBucket->m_rgKeys[i] == key) // keys match
// Acquire load: ensures the value load below is ordered
// after the key load. Pairs with the release store in
// Bucket::InsertValue.
if (VolatileLoad(&pBucket->m_rgKeys[i]) == key) // keys match
{

// inline memory barrier call, refer to
// function description at the beginning of this
MemoryBarrier();

UPTR storedVal = pBucket->GetValue(i);
// if compare function is provided
// dupe keys are possible, check if the value matches,
Expand Down Expand Up @@ -661,27 +656,26 @@ UPTR HashMap::ReplaceValue(UPTR key, UPTR value)
Bucket* pBucket = &rgBuckets[seed % cbSize];
for (unsigned int i = 0; i < SLOTS_PER_BUCKET; i++)
{
if (pBucket->m_rgKeys[i] == key) // keys match
// Acquire load: ensures the value load below observes the
// value that was stored when this key was first published
// via Bucket::InsertValue.
if (VolatileLoad(&pBucket->m_rgKeys[i]) == key) // keys match
{

// inline memory barrier call, refer to
// function description at the beginning of this
MemoryBarrier();

UPTR storedVal = pBucket->GetValue(i);
// if compare function is provided
// dupe keys are possible, check if the value matches,
if (CompareValues(value,storedVal))
{
ProfileLookup(ntry,storedVal); //no-op in non HASHTABLE_PROFILE code

// Plain store the new value, then release-store the
// key to re-publish it. Readers acquire-load the key
// via VolatileLoad(&m_rgKeys[i]), forming a proper
// release-acquire pair on the same address and
// ensuring they observe either the old or fully-
// updated new value.
pBucket->SetValue(value, i);

// On multiprocessors we should make sure that
// the value is propagated before we proceed.
// inline memory barrier call, refer to
// function description at the beginning of this
MemoryBarrier();
VolatileStore(&pBucket->m_rgKeys[i], key);

// return the previous stored value
return storedVal;
Expand Down Expand Up @@ -737,12 +731,11 @@ UPTR HashMap::DeleteValue (UPTR key, UPTR value)
Bucket* pBucket = &rgBuckets[seed % cbSize];
for (unsigned int i = 0; i < SLOTS_PER_BUCKET; i++)
{
if (pBucket->m_rgKeys[i] == key) // keys match
// Acquire load: ensures the value load below is ordered
// after the key load. Pairs with the release store in
// Bucket::InsertValue.
if (VolatileLoad(&pBucket->m_rgKeys[i]) == key) // keys match
{
// inline memory barrier call, refer to
// function description at the beginning of this
MemoryBarrier();

UPTR storedVal = pBucket->GetValue(i);
// if compare function is provided
// dupe keys are possible, check if the value matches,
Expand Down Expand Up @@ -960,11 +953,12 @@ void HashMap::Rehash()
rgCurrentBuckets = NULL;
currentBucketsSize = 0;

// memory barrier, to replace the pointer to array of bucket
MemoryBarrier();

// Update the HashMap state
m_rgBuckets = rgNewBuckets;
// Release store: ensures all writes to the new bucket array are
// visible before the pointer is published. Readers observe these
// writes because they enter an EBR critical region (see
// EbrCriticalRegionHolder::EnterCriticalRegion and Buckets()), which
// executes a full MemoryBarrier() before reading m_rgBuckets.
VolatileStore(&m_rgBuckets, rgNewBuckets);
m_iPrimeIndex = newPrimeIndex;
m_cbInserts = cbValidSlotsInit; // reset insert count to the new valid count
m_cbPrevSlotsInUse = cbValidSlotsInit; // track the previous delete count
Expand Down
Loading