--- /dev/null
+/*------------------------------------------------------------------------
+ Junction: Concurrent data structures in C++
+ Copyright (c) 2016 Jeff Preshing
+
+ Distributed under the Simplified BSD License.
+ Original location: https://github.com/preshing/junction
+
+ This software is distributed WITHOUT ANY WARRANTY; without even the
+ implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
+ See the LICENSE file for more information.
+------------------------------------------------------------------------*/
+
+#ifndef JUNCTION_DETAILS_LEAPFROG_H
+#define JUNCTION_DETAILS_LEAPFROG_H
+
+#include <junction/Core.h>
+#include <turf/Atomic.h>
+#include <turf/Mutex.h>
+#include <turf/ManualResetEvent.h>
+#include <turf/Util.h>
+#include <junction/MapTraits.h>
+#include <turf/Trace.h>
+#include <turf/Heap.h>
+#include <junction/SimpleJobCoordinator.h>
+#include <junction/QSBR.h>
+
+// Enable this to force migration overflows (for test purposes):
+#define JUNCTION_LEAPFROG_FORCE_MIGRATION_OVERFLOWS 0
+
+namespace junction {
+namespace details {
+
+TURF_TRACE_DECLARE(Leapfrog, 33)
+
+template <class Map>
+struct Leapfrog {
+ typedef typename Map::Hash Hash;
+ typedef typename Map::Value Value;
+ typedef typename Map::KeyTraits KeyTraits;
+ typedef typename Map::ValueTraits ValueTraits;
+
+ static const ureg InitialSize = 8;
+ static const ureg TableMigrationUnitSize = 32;
+ static const ureg LinearSearchLimit = 128;
+ static const ureg CellsInUseSample = LinearSearchLimit;
+ TURF_STATIC_ASSERT(LinearSearchLimit > 0 && LinearSearchLimit < 256); // Must fit in CellGroup::links
+ TURF_STATIC_ASSERT(CellsInUseSample > 0 && CellsInUseSample <= LinearSearchLimit); // Limit sample to failed search chain
+
+ struct Cell {
+ turf::Atomic<Hash> hash;
+ turf::Atomic<Value> value;
+ };
+
+ struct CellGroup {
+ // Every cell in the table actually represents a bucket of cells, all linked together in a probe chain.
+ // Each cell in the probe chain is located within the table itself.
+ // "deltas" determines the index of the next cell in the probe chain.
+ // The first cell in the chain is the one that was hashed. It may or may not actually belong in the bucket.
+ // The "second" cell in the chain is given by deltas 0 - 3. It's guaranteed to belong in the bucket.
+ // All subsequent cells in the chain is given by deltas 4 - 7. Also guaranteed to belong in the bucket.
+ turf::Atomic<u8> deltas[8];
+ Cell cells[4];
+ };
+
+ struct Table {
+ const ureg sizeMask; // a power of two minus one
+ turf::Mutex mutex; // to DCLI the TableMigration (stored in the jobCoordinator)
+ SimpleJobCoordinator jobCoordinator; // makes all blocked threads participate in the migration
+
+ Table(ureg sizeMask) : sizeMask(sizeMask) {
+ }
+
+ static Table* create(ureg tableSize) {
+ TURF_ASSERT(turf::util::isPowerOf2(tableSize));
+ TURF_ASSERT(tableSize >= 4);
+ ureg numGroups = tableSize >> 2;
+ Table* table = (Table*) TURF_HEAP.alloc(sizeof(Table) + sizeof(CellGroup) * numGroups);
+ new (table) Table(tableSize - 1);
+ for (ureg i = 0; i < numGroups; i++) {
+ CellGroup* group = table->getCellGroups() + i;
+ for (ureg j = 0; j < 4; j++) {
+ group->deltas[j].storeNonatomic(0);
+ group->deltas[j + 4].storeNonatomic(0);
+ group->cells[j].hash.storeNonatomic(KeyTraits::NullHash);
+ group->cells[j].value.storeNonatomic(Value(ValueTraits::NullValue));
+ }
+ }
+ return table;
+ }
+
+ void destroy() {
+ this->Table::~Table();
+ TURF_HEAP.free(this);
+ }
+
+ CellGroup* getCellGroups() const {
+ return (CellGroup*) (this + 1);
+ }
+
+ ureg getNumMigrationUnits() const {
+ return sizeMask / TableMigrationUnitSize + 1;
+ }
+ };
+
+ class TableMigration : public SimpleJobCoordinator::Job {
+ public:
+ struct Source {
+ Table* table;
+ turf::Atomic<ureg> sourceIndex;
+ };
+
+ Map& m_map;
+ Table* m_destination;
+ turf::Atomic<ureg> m_workerStatus; // number of workers + end flag
+ turf::Atomic<bool> m_overflowed;
+ turf::Atomic<sreg> m_unitsRemaining;
+ ureg m_numSources;
+
+ TableMigration(Map& map) : m_map(map) {
+ }
+
+ static TableMigration* create(Map& map, ureg numSources) {
+ TableMigration* migration =
+ (TableMigration*) TURF_HEAP.alloc(sizeof(TableMigration) + sizeof(TableMigration::Source) * numSources);
+ new (migration) TableMigration(map);
+ migration->m_workerStatus.storeNonatomic(0);
+ migration->m_overflowed.storeNonatomic(false);
+ migration->m_unitsRemaining.storeNonatomic(0);
+ migration->m_numSources = numSources;
+ // Caller is responsible for filling in sources & destination
+ return migration;
+ }
+
+ virtual ~TableMigration() TURF_OVERRIDE {
+ }
+
+ void destroy() {
+ // Destroy all source tables.
+ for (ureg i = 0; i < m_numSources; i++)
+ if (getSources()[i].table)
+ getSources()[i].table->destroy();
+ // Delete the migration object itself.
+ this->TableMigration::~TableMigration();
+ TURF_HEAP.free(this);
+ }
+
+ Source* getSources() const {
+ return (Source*) (this + 1);
+ }
+
+ bool migrateRange(Table* srcTable, ureg startIdx);
+ virtual void run() TURF_OVERRIDE;
+ };
+
+ static Cell* find(Hash hash, Table* table) {
+ TURF_TRACE(Leapfrog, 0, "[find] called", uptr(table), hash);
+ TURF_ASSERT(table);
+ TURF_ASSERT(hash != KeyTraits::NullHash);
+ ureg sizeMask = table->sizeMask;
+ // Optimistically check hashed cell even though it might belong to another bucket
+ ureg idx = hash & sizeMask;
+ CellGroup* group = table->getCellGroups() + (idx >> 2);
+ Cell* cell = group->cells + (idx & 3);
+ Hash probeHash = cell->hash.load(turf::Relaxed);
+ if (probeHash == hash) {
+ TURF_TRACE(Leapfrog, 1, "[find] found existing cell optimistically", uptr(table), idx);
+ return cell;
+ } else if (probeHash == KeyTraits::NullHash) {
+ return cell = NULL;
+ }
+ // Follow probe chain for our bucket
+ u8 delta = group->deltas[idx & 3].load(turf::Relaxed);
+ while (delta) {
+ idx = (idx + delta) & sizeMask;
+ group = table->getCellGroups() + (idx >> 2);
+ cell = group->cells + (idx & 3);
+ Hash probeHash = cell->hash.load(turf::Relaxed);
+ // Note: probeHash might actually be NULL due to memory reordering of a concurrent insert,
+ // but we don't check for it. We just follow the probe chain.
+ if (probeHash == hash) {
+ TURF_TRACE(Leapfrog, 2, "[find] found existing cell", uptr(table), idx);
+ return cell;
+ }
+ delta = group->deltas[(idx & 3) + 4].load(turf::Relaxed);
+ }
+ // End of probe chain, not found
+ return NULL;
+ }
+
+ // FIXME: Possible optimization: Dedicated insert for migration? It wouldn't check for InsertResult_AlreadyFound.
+ enum InsertResult { InsertResult_AlreadyFound, InsertResult_InsertedNew, InsertResult_Overflow };
+ static InsertResult insertOrFind(Hash hash, Table* table, Cell*& cell, ureg& overflowIdx) {
+ TURF_TRACE(Leapfrog, 3, "[insertOrFind] called", uptr(table), hash);
+ TURF_ASSERT(table);
+ TURF_ASSERT(hash != KeyTraits::NullHash);
+ ureg sizeMask = table->sizeMask;
+ ureg idx = ureg(hash);
+
+ // Check hashed cell first, though it may not even belong to the bucket.
+ CellGroup* group = table->getCellGroups() + ((idx & sizeMask) >> 2);
+ cell = group->cells + (idx & 3);
+ Hash probeHash = cell->hash.load(turf::Relaxed);
+ if (probeHash == KeyTraits::NullHash) {
+ if (cell->hash.compareExchangeStrong(probeHash, hash, turf::Relaxed)) {
+ TURF_TRACE(Leapfrog, 4, "[insertOrFind] reserved first cell", uptr(table), idx);
+ // There are no links to set. We're done.
+ return InsertResult_InsertedNew;
+ } else {
+ TURF_TRACE(Leapfrog, 5, "[insertOrFind] race to reserve first cell", uptr(table), idx);
+ // Fall through to check if it was the same hash...
+ }
+ }
+ if (probeHash == hash) {
+ TURF_TRACE(Leapfrog, 6, "[insertOrFind] found in first cell", uptr(table), idx);
+ return InsertResult_AlreadyFound;
+ }
+
+ // Follow the link chain for this bucket.
+ ureg maxIdx = idx + sizeMask;
+ ureg linkLevel = 0;
+ turf::Atomic<u8>* prevLink;
+ for (;;) {
+ followLink:
+ prevLink = group->deltas + ((idx & 3) + linkLevel);
+ linkLevel = 4;
+ u8 probeDelta = prevLink->load(turf::Relaxed);
+ if (probeDelta) {
+ idx += probeDelta;
+ // Check the hash for this cell.
+ group = table->getCellGroups() + ((idx & sizeMask) >> 2);
+ cell = group->cells + (idx & 3);
+ probeHash = cell->hash.load(turf::Relaxed);
+ if (probeHash == KeyTraits::NullHash) {
+ // Cell was linked, but hash is not visible yet.
+ // We could avoid this case (and guarantee it's visible) using acquire & release, but instead,
+ // just poll until it becomes visible.
+ TURF_TRACE(Leapfrog, 7, "[insertOrFind] race to read hash", uptr(table), idx);
+ do {
+ probeHash = cell->hash.load(turf::Acquire);
+ } while (probeHash == KeyTraits::NullHash);
+ }
+ TURF_ASSERT(((probeHash ^ hash) & sizeMask) == 0); // Only hashes in same bucket can be linked
+ if (probeHash == hash) {
+ TURF_TRACE(Leapfrog, 8, "[insertOrFind] found in probe chain", uptr(table), idx);
+ return InsertResult_AlreadyFound;
+ }
+ } else {
+ // Reached the end of the link chain for this bucket.
+ // Switch to linear probing until we reserve a new cell or find a late-arriving cell in the same bucket.
+ ureg prevLinkIdx = idx;
+ TURF_ASSERT(sreg(maxIdx - idx) >= 0); // Nobody would have linked an idx that's out of range.
+ ureg linearProbesRemaining = turf::util::min(maxIdx - idx, LinearSearchLimit);
+ while (linearProbesRemaining-- > 0) {
+ idx++;
+ group = table->getCellGroups() + ((idx & sizeMask) >> 2);
+ cell = group->cells + (idx & 3);
+ probeHash = cell->hash.load(turf::Relaxed);
+ if (probeHash == KeyTraits::NullHash) {
+ // It's an empty cell. Try to reserve it.
+ if (cell->hash.compareExchangeStrong(probeHash, hash, turf::Relaxed)) {
+ // Success. We've reserved the cell. Link it to previous cell in same bucket.
+ TURF_TRACE(Leapfrog, 9, "[insertOrFind] reserved cell", uptr(table), idx);
+ TURF_ASSERT(probeDelta == 0);
+ u8 desiredDelta = idx - prevLinkIdx;
+#if TURF_WITH_ASSERTS
+ probeDelta = prevLink->exchange(desiredDelta, turf::Relaxed);
+ TURF_ASSERT(probeDelta == 0 || probeDelta == desiredDelta);
+#else
+ prevLink->store(desiredDelta, turf::Relaxed);
+#endif
+ return InsertResult_InsertedNew;
+ } else {
+ TURF_TRACE(Leapfrog, 10, "[insertOrFind] race to reserve cell", uptr(table), idx);
+ // Fall through to check if it's the same hash...
+ }
+ }
+ Hash x = (probeHash ^ hash);
+ // Check for same hash.
+ if (!x) {
+ TURF_TRACE(Leapfrog, 11, "[insertOrFind] found outside probe chain", uptr(table), idx);
+ return InsertResult_AlreadyFound;
+ }
+ // Check for same bucket.
+ if ((x & sizeMask) == 0) {
+ TURF_TRACE(Leapfrog, 12, "[insertOrFind] found late-arriving cell in same bucket", uptr(table), idx);
+ // Attempt to set the link on behalf of the late-arriving cell.
+ // This is usually redundant, but if we don't attempt to set the late-arriving cell's link here,
+ // there's no guarantee that our own link chain will be well-formed by the time this function returns.
+ // (Indeed, subsequent lookups sometimes failed during testing, for this exact reason.)
+ u8 desiredDelta = idx - prevLinkIdx;
+#if TURF_WITH_ASSERTS
+ probeDelta = prevLink->exchange(desiredDelta, turf::Relaxed);
+ TURF_ASSERT(probeDelta == 0 || probeDelta == desiredDelta);
+ if (probeDelta == 0)
+ TURF_TRACE(Leapfrog, 13, "[insertOrFind] set link on behalf of late-arriving cell", uptr(table), idx);
+#else
+ prevLink->store(desiredDelta, turf::Relaxed);
+#endif
+ goto followLink; // Try to follow link chain for the bucket again.
+ }
+ // Continue linear search...
+ }
+ // Table is too full to insert.
+ overflowIdx = idx + 1;
+ TURF_TRACE(Leapfrog, 14, "[insertOrFind] overflow", uptr(table), overflowIdx);
+ return InsertResult_Overflow;
+ }
+ }
+ }
+
+ static void beginTableMigrationToSize(Map& map, Table* table, ureg nextTableSize) {
+ // Create new migration by DCLI.
+ TURF_TRACE(Leapfrog, 15, "[beginTableMigrationToSize] called", 0, 0);
+ SimpleJobCoordinator::Job* job = table->jobCoordinator.loadConsume();
+ if (job) {
+ TURF_TRACE(Leapfrog, 16, "[beginTableMigrationToSize] new migration already exists", 0, 0);
+ } else {
+ turf::LockGuard<turf::Mutex> guard(table->mutex);
+ job = table->jobCoordinator.loadConsume(); // Non-atomic would be sufficient, but that's OK.
+ if (job) {
+ TURF_TRACE(Leapfrog, 17, "[beginTableMigrationToSize] new migration already exists (double-checked)", 0, 0);
+ } else {
+ // Create new migration.
+ TableMigration* migration = TableMigration::create(map, 1);
+ migration->m_unitsRemaining.storeNonatomic(table->getNumMigrationUnits());
+ migration->getSources()[0].table = table;
+ migration->getSources()[0].sourceIndex.storeNonatomic(0);
+ migration->m_destination = Table::create(nextTableSize);
+ // Publish the new migration.
+ table->jobCoordinator.storeRelease(migration);
+ }
+ }
+ }
+
+ static void beginTableMigration(Map& map, Table* table, ureg overflowIdx) {
+ // Estimate number of cells in use based on a small sample.
+ ureg sizeMask = table->sizeMask;
+ ureg idx = overflowIdx - CellsInUseSample;
+ ureg inUseCells = 0;
+ for (ureg linearProbesRemaining = CellsInUseSample; linearProbesRemaining > 0; linearProbesRemaining--) {
+ CellGroup* group = table->getCellGroups() + ((idx & sizeMask) >> 2);
+ Cell* cell = group->cells + (idx & 3);
+ Value value = cell->value.load(turf::Relaxed);
+ if (value == Value(ValueTraits::Redirect)) {
+ // Another thread kicked off the jobCoordinator. The caller will participate upon return.
+ TURF_TRACE(Leapfrog, 18, "[beginTableMigration] redirected while determining table size", 0, 0);
+ return;
+ }
+ if (value != Value(ValueTraits::NullValue))
+ inUseCells++;
+ idx++;
+ }
+ float inUseRatio = float(inUseCells) / CellsInUseSample;
+ float estimatedInUse = (sizeMask + 1) * inUseRatio;
+#if JUNCTION_LEAPFROG_FORCE_MIGRATION_OVERFLOWS
+ // Periodically underestimate the number of cells in use.
+ // This exercises the code that handles overflow during migration.
+ static ureg counter = 1;
+ if ((++counter & 3) == 0) {
+ estimatedInUse /= 4;
+ }
+#endif
+ ureg nextTableSize = turf::util::max(InitialSize, turf::util::roundUpPowerOf2(ureg(estimatedInUse * 2)));
+ beginTableMigrationToSize(map, table, nextTableSize);
+ }
+}; // Leapfrog
+
+template <class Map>
+bool Leapfrog<Map>::TableMigration::migrateRange(Table* srcTable, ureg startIdx) {
+ ureg srcSizeMask = srcTable->sizeMask;
+ ureg endIdx = turf::util::min(startIdx + TableMigrationUnitSize, srcSizeMask + 1);
+ // Iterate over source range.
+ for (ureg srcIdx = startIdx; srcIdx < endIdx; srcIdx++) {
+ CellGroup* srcGroup = srcTable->getCellGroups() + ((srcIdx & srcSizeMask) >> 2);
+ Cell* srcCell = srcGroup->cells + (srcIdx & 3);
+ Hash srcHash;
+ Value srcValue;
+ // Fetch the srcHash and srcValue.
+ for (;;) {
+ srcHash = srcCell->hash.load(turf::Relaxed);
+ if (srcHash == KeyTraits::NullHash) {
+ // An unused cell. Try to put a Redirect marker in its value.
+ srcValue =
+ srcCell->value.compareExchange(Value(ValueTraits::NullValue), Value(ValueTraits::Redirect), turf::Relaxed);
+ if (srcValue == Value(ValueTraits::Redirect)) {
+ // srcValue is already marked Redirect due to previous incomplete migration.
+ TURF_TRACE(Leapfrog, 19, "[migrateRange] empty cell already redirected", uptr(srcTable), srcIdx);
+ break;
+ }
+ if (srcValue == Value(ValueTraits::NullValue))
+ break; // Redirect has been placed. Break inner loop, continue outer loop.
+ TURF_TRACE(Leapfrog, 20, "[migrateRange] race to insert key", uptr(srcTable), srcIdx);
+ // Otherwise, somebody just claimed the cell. Read srcHash again...
+ } else {
+ // Check for deleted/uninitialized value.
+ srcValue = srcCell->value.load(turf::Relaxed);
+ if (srcValue == Value(ValueTraits::NullValue)) {
+ // Try to put a Redirect marker.
+ if (srcCell->value.compareExchangeStrong(srcValue, Value(ValueTraits::Redirect), turf::Relaxed))
+ break; // Redirect has been placed. Break inner loop, continue outer loop.
+ TURF_TRACE(Leapfrog, 21, "[migrateRange] race to insert value", uptr(srcTable), srcIdx);
+ if (srcValue == Value(ValueTraits::Redirect)) {
+ // FIXME: I don't think this will happen. Investigate & change to assert
+ TURF_TRACE(Leapfrog, 22, "[migrateRange] race inserted Redirect", uptr(srcTable), srcIdx);
+ break;
+ }
+ } else if (srcValue == Value(ValueTraits::Redirect)) {
+ // srcValue is already marked Redirect due to previous incomplete migration.
+ TURF_TRACE(Leapfrog, 23, "[migrateRange] in-use cell already redirected", uptr(srcTable), srcIdx);
+ break;
+ }
+
+ // We've got a key/value pair to migrate.
+ // Reserve a destination cell in the destination.
+ TURF_ASSERT(srcHash != KeyTraits::NullHash);
+ TURF_ASSERT(srcValue != Value(ValueTraits::NullValue));
+ TURF_ASSERT(srcValue != Value(ValueTraits::Redirect));
+ Cell* dstCell;
+ ureg overflowIdx;
+ InsertResult result = insertOrFind(srcHash, m_destination, dstCell, overflowIdx);
+ // During migration, a hash can only exist in one place among all the source tables,
+ // and it is only migrated by one thread. Therefore, the hash will never already exist
+ // in the destination table:
+ TURF_ASSERT(result != InsertResult_AlreadyFound);
+ if (result == InsertResult_Overflow) {
+ // Destination overflow.
+ // This can happen for several reasons. For example, the source table could have
+ // existed of all deleted cells when it overflowed, resulting in a small destination
+ // table size, but then another thread could re-insert all the same hashes
+ // before the migration completed.
+ // Caller will cancel the current migration and begin a new one.
+ return false;
+ }
+ // Migrate the old value to the new cell.
+ for (;;) {
+ // Copy srcValue to the destination.
+ dstCell->value.store(srcValue, turf::Relaxed);
+ // Try to place a Redirect marker in srcValue.
+ Value doubleCheckedSrcValue =
+ srcCell->value.compareExchange(srcValue, Value(ValueTraits::Redirect), turf::Relaxed);
+ TURF_ASSERT(doubleCheckedSrcValue !=
+ Value(ValueTraits::Redirect)); // Only one thread can redirect a cell at a time.
+ if (doubleCheckedSrcValue == srcValue) {
+ // No racing writes to the src. We've successfully placed the Redirect marker.
+ // srcValue was non-NULL when we decided to migrate it, but it may have changed to NULL
+ // by a late-arriving erase.
+ if (srcValue == Value(ValueTraits::NullValue))
+ TURF_TRACE(Leapfrog, 24, "[migrateRange] racing update was erase", uptr(srcTable), srcIdx);
+ break;
+ }
+ // There was a late-arriving write (or erase) to the src. Migrate the new value and try again.
+ TURF_TRACE(Leapfrog, 25, "[migrateRange] race to update migrated value", uptr(srcTable), srcIdx);
+ srcValue = doubleCheckedSrcValue;
+ }
+ // Cell successfully migrated. Proceed to next source cell.
+ break;
+ }
+ }
+ }
+ // Range has been migrated successfully.
+ return true;
+}
+
+template <class Map>
+void Leapfrog<Map>::TableMigration::run() {
+ // Conditionally increment the shared # of workers.
+ ureg probeStatus = m_workerStatus.load(turf::Relaxed);
+ do {
+ if (probeStatus & 1) {
+ // End flag is already set, so do nothing.
+ TURF_TRACE(Leapfrog, 26, "[TableMigration::run] already ended", uptr(this), 0);
+ return;
+ }
+ } while (!m_workerStatus.compareExchangeWeak(probeStatus, probeStatus + 2, turf::Relaxed, turf::Relaxed));
+ // # of workers has been incremented, and the end flag is clear.
+ TURF_ASSERT((probeStatus & 1) == 0);
+
+ // Iterate over all source tables.
+ for (ureg s = 0; s < m_numSources; s++) {
+ Source& source = getSources()[s];
+ // Loop over all migration units in this source table.
+ for (;;) {
+ if (m_workerStatus.load(turf::Relaxed) & 1) {
+ TURF_TRACE(Leapfrog, 27, "[TableMigration::run] detected end flag set", uptr(this), 0);
+ goto endMigration;
+ }
+ ureg startIdx = source.sourceIndex.fetchAdd(TableMigrationUnitSize, turf::Relaxed);
+ if (startIdx >= source.table->sizeMask + 1)
+ break; // No more migration units in this table. Try next source table.
+ bool overflowed = !migrateRange(source.table, startIdx);
+ if (overflowed) {
+ // *** FAILED MIGRATION ***
+ // TableMigration failed due to destination table overflow.
+ // No other thread can declare the migration successful at this point, because *this* unit will never complete,
+ // hence m_unitsRemaining won't reach zero.
+ // However, multiple threads can independently detect a failed migration at the same time.
+ TURF_TRACE(Leapfrog, 28, "[TableMigration::run] destination overflow", uptr(source.table), uptr(startIdx));
+ // The reason we store overflowed in a shared variable is because we can must flush all the worker threads before
+ // we can safely deal with the overflow. Therefore, the thread that detects the failure is often different from
+ // the thread
+ // that deals with it.
+ bool oldOverflowed = m_overflowed.exchange(overflowed, turf::Relaxed);
+ if (oldOverflowed)
+ TURF_TRACE(Leapfrog, 29, "[TableMigration::run] race to set m_overflowed", uptr(overflowed),
+ uptr(oldOverflowed));
+ m_workerStatus.fetchOr(1, turf::Relaxed);
+ goto endMigration;
+ }
+ sreg prevRemaining = m_unitsRemaining.fetchSub(1, turf::Relaxed);
+ TURF_ASSERT(prevRemaining > 0);
+ if (prevRemaining == 1) {
+ // *** SUCCESSFUL MIGRATION ***
+ // That was the last chunk to migrate.
+ m_workerStatus.fetchOr(1, turf::Relaxed);
+ goto endMigration;
+ }
+ }
+ }
+ TURF_TRACE(Leapfrog, 30, "[TableMigration::run] out of migration units", uptr(this), 0);
+
+endMigration:
+ // Decrement the shared # of workers.
+ probeStatus = m_workerStatus.fetchSub(
+ 2, turf::AcquireRelease); // AcquireRelease makes all previous writes visible to the last worker thread.
+ if (probeStatus >= 4) {
+ // There are other workers remaining. Return here so that only the very last worker will proceed.
+ TURF_TRACE(Leapfrog, 31, "[TableMigration::run] not the last worker", uptr(this), uptr(probeStatus));
+ return;
+ }
+
+ // We're the very last worker thread.
+ // Perform the appropriate post-migration step depending on whether the migration succeeded or failed.
+ TURF_ASSERT(probeStatus == 3);
+ bool overflowed = m_overflowed.loadNonatomic(); // No racing writes at this point
+ if (!overflowed) {
+ // The migration succeeded. This is the most likely outcome. Publish the new subtree.
+ m_map.publishTableMigration(this);
+ // End the jobCoodinator.
+ getSources()[0].table->jobCoordinator.end();
+ } else {
+ // The migration failed due to the overflow of the destination table.
+ Table* origTable = getSources()[0].table;
+ turf::LockGuard<turf::Mutex> guard(origTable->mutex);
+ SimpleJobCoordinator::Job* checkedJob = origTable->jobCoordinator.loadConsume();
+ if (checkedJob != this) {
+ TURF_TRACE(Leapfrog, 32, "[TableMigration::run] a new TableMigration was already started", uptr(origTable),
+ uptr(checkedJob));
+ } else {
+ TableMigration* migration = TableMigration::create(m_map, m_numSources + 1);
+ // Double the destination table size.
+ migration->m_destination = Table::create((m_destination->sizeMask + 1) * 2);
+ // Transfer source tables to the new migration.
+ for (ureg i = 0; i < m_numSources; i++) {
+ migration->getSources()[i].table = getSources()[i].table;
+ getSources()[i].table = NULL;
+ migration->getSources()[i].sourceIndex.storeNonatomic(0);
+ }
+ migration->getSources()[m_numSources].table = m_destination;
+ migration->getSources()[m_numSources].sourceIndex.storeNonatomic(0);
+ // Calculate total number of migration units to move.
+ ureg unitsRemaining = 0;
+ for (ureg s = 0; s < migration->m_numSources; s++)
+ unitsRemaining += migration->getSources()[s].table->getNumMigrationUnits();
+ migration->m_unitsRemaining.storeNonatomic(unitsRemaining);
+ // Publish the new migration.
+ origTable->jobCoordinator.storeRelease(migration);
+ }
+ }
+
+ // We're done with this TableMigration. Queue it for GC.
+ DefaultQSBR.enqueue(&TableMigration::destroy, this);
+}
+
+} // namespace details
+} // namespace junction
+
+#endif // JUNCTION_DETAILS_LEAPFROG_H
projects / junction.git / blobdiff