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8207359: Make SymbolTable increment_refcount disallow zero

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Use cmpxchg for non permanent symbol refcounting, and pack refcount and length into an int.

Reviewed-by: gziemski, kbarrett, iklam
This commit is contained in:
Coleen Phillimore 2018-07-20 14:52:11 -04:00
parent 6cbef1de5d
commit 39dd04b953
14 changed files with 206 additions and 64 deletions
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17
src/hotspot/share/classfile/symbolTable.cpp
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@ -1,5 +1,5 @@
/*
* Copyright (c) 1997, 2017, Oracle and/or its affiliates. All rights reserved.
* Copyright (c) 1997, 2018, Oracle and/or its affiliates. All rights reserved.
* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
*
* This code is free software; you can redistribute it and/or modify it
@ -190,6 +190,7 @@ void SymbolTable::rehash_table() {
assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
// This should never happen with -Xshare:dump but it might in testing mode.
if (DumpSharedSpaces) return;
// Create a new symbol table
SymbolTable* new_table = new SymbolTable();
@ -212,10 +213,16 @@ Symbol* SymbolTable::lookup_dynamic(int index, const char* name,
count++; // count all entries in this bucket, not just ones with same hash
if (e->hash() == hash) {
Symbol* sym = e->literal();
if (sym->equals(name, len)) {
// something is referencing this symbol now.
sym->increment_refcount();
return sym;
// Skip checking already dead symbols in the bucket.
if (sym->refcount() == 0) {
count--; // Don't count this symbol towards rehashing.
} else if (sym->equals(name, len)) {
if (sym->try_increment_refcount()) {
// something is referencing this symbol now.
return sym;
} else {
count--; // don't count this symbol.
}
}
}
}