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8191786: Thread-SMR hash table size should be dynamic #4168

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8191786: Thread-SMR hash table size should be dynamic #4168

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8191786: Thread-SMR hash table size should be dynamic
dcubed-ojdk May 22, 2021
0e4db02
rehn CR
dcubed-ojdk May 25, 2021
b57ebc2
Rewind and remove the unused hash_table_size calculations; ThreadScan…
dcubed-ojdk May 27, 2021
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21 changes: 5 additions & 16 deletions src/hotspot/share/runtime/threadSMR.cpp
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Expand Up @@ -192,10 +192,8 @@ class ThreadScanHashtable : public CHeapObj<mtThread> {
return (unsigned int)(((uint32_t)(uintptr_t)s1) * 2654435761u);
}

int _table_size;
// ResourceHashtable SIZE is specified at compile time so our
// dynamic _table_size is unused for now; 1031 is the first prime
// after 1024.
// ResourceHashtable SIZE is specified at compile time so we
// use 1031 which is the first prime after 1024.
typedef ResourceHashtable<void *, int, &ThreadScanHashtable::ptr_hash,
&ThreadScanHashtable::ptr_equals, 1031,
ResourceObj::C_HEAP, mtThread> PtrTable;
Expand All @@ -205,7 +203,7 @@ class ThreadScanHashtable : public CHeapObj<mtThread> {
// ResourceHashtable is passed to various functions and populated in
// different places so we allocate it using C_HEAP to make it immune
// from any ResourceMarks that happen to be in the code paths.
ThreadScanHashtable(int table_size) : _table_size(table_size), _ptrs(new (ResourceObj::C_HEAP, mtThread) PtrTable()) {}
ThreadScanHashtable() : _ptrs(new (ResourceObj::C_HEAP, mtThread) PtrTable()) {}

~ThreadScanHashtable() { delete _ptrs; }

Expand Down Expand Up @@ -870,12 +868,8 @@ void ThreadsSMRSupport::free_list(ThreadsList* threads) {
}
}

// Hash table size should be first power of two higher than twice the length of the ThreadsList
int hash_table_size = MIN2((int)get_java_thread_list()->length(), 32) << 1;
hash_table_size = round_up_power_of_2(hash_table_size);

// Gather a hash table of the current hazard ptrs:
ThreadScanHashtable *scan_table = new ThreadScanHashtable(hash_table_size);
ThreadScanHashtable *scan_table = new ThreadScanHashtable();
ScanHazardPtrGatherThreadsListClosure scan_cl(scan_table);
threads_do(&scan_cl);
OrderAccess::acquire(); // Must order reads of hazard ptr before reads of
Expand Down Expand Up @@ -929,14 +923,9 @@ void ThreadsSMRSupport::free_list(ThreadsList* threads) {
bool ThreadsSMRSupport::is_a_protected_JavaThread(JavaThread *thread) {
assert_locked_or_safepoint(Threads_lock);

// Hash table size should be first power of two higher than twice
// the length of the Threads list.
int hash_table_size = MIN2((int)get_java_thread_list()->length(), 32) << 1;
hash_table_size = round_up_power_of_2(hash_table_size);

// Gather a hash table of the JavaThreads indirectly referenced by
// hazard ptrs.
ThreadScanHashtable *scan_table = new ThreadScanHashtable(hash_table_size);
ThreadScanHashtable *scan_table = new ThreadScanHashtable();
ScanHazardPtrGatherProtectedThreadsClosure scan_cl(scan_table);
threads_do(&scan_cl);
OrderAccess::acquire(); // Must order reads of hazard ptr before reads of
Expand Down