mirror of git://gcc.gnu.org/git/gcc.git
106 lines
3.8 KiB
C++
106 lines
3.8 KiB
C++
/* Copyright (C) 2011-2016 Free Software Foundation, Inc.
|
|
Contributed by Torvald Riegel <triegel@redhat.com>.
|
|
|
|
This file is part of the GNU Transactional Memory Library (libitm).
|
|
|
|
Libitm is free software; you can redistribute it and/or modify it
|
|
under the terms of the GNU General Public License as published by
|
|
the Free Software Foundation; either version 3 of the License, or
|
|
(at your option) any later version.
|
|
|
|
Libitm is distributed in the hope that it will be useful, but WITHOUT ANY
|
|
WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
|
|
FOR A PARTICULAR PURPOSE. See the GNU General Public License for
|
|
more details.
|
|
|
|
Under Section 7 of GPL version 3, you are granted additional
|
|
permissions described in the GCC Runtime Library Exception, version
|
|
3.1, as published by the Free Software Foundation.
|
|
|
|
You should have received a copy of the GNU General Public License and
|
|
a copy of the GCC Runtime Library Exception along with this program;
|
|
see the files COPYING3 and COPYING.RUNTIME respectively. If not, see
|
|
<http://www.gnu.org/licenses/>. */
|
|
|
|
#ifndef GTM_RWLOCK_H
|
|
#define GTM_RWLOCK_H
|
|
|
|
#include "local_atomic"
|
|
#include "common.h"
|
|
|
|
namespace GTM HIDDEN {
|
|
|
|
struct gtm_thread;
|
|
|
|
// This datastructure is the blocking, futex-based version of the Dekker-style
|
|
// reader-writer lock used to provide mutual exclusion between active and
|
|
// serial transactions.
|
|
// See libitm's documentation for further details.
|
|
//
|
|
// In this implementation, writers are given highest priority access but
|
|
// read-to-write upgrades do not have a higher priority than writers.
|
|
//
|
|
// Do not change the layout of this class; it must remain a POD type with
|
|
// standard layout, and the writers field must be first (i.e., so the
|
|
// assembler code can assume that its address is equal to the address of the
|
|
// respective instance of the class), and htm_fastpath must be second.
|
|
|
|
class gtm_rwlock
|
|
{
|
|
std::atomic<int> writers; // Writers' futex.
|
|
// We put the HTM fastpath control variable here so that HTM fastpath
|
|
// transactions can check efficiently whether they are allowed to run.
|
|
// This must be accessed atomically because threads can load this value
|
|
// when they are neither a registered reader nor writer (i.e., when they
|
|
// attempt to execute the HTM fastpath).
|
|
std::atomic<uint32_t> htm_fastpath;
|
|
// TODO Put these futexes on different cachelines? (writers and htm_fastpath
|
|
// should remain on the same cacheline.
|
|
std::atomic<int> writer_readers;// A confirmed writer waits here for readers.
|
|
std::atomic<int> readers; // Readers wait here for writers (iff true).
|
|
|
|
public:
|
|
gtm_rwlock() : writers(0), htm_fastpath(0), writer_readers(0), readers(0)
|
|
{ }
|
|
|
|
void read_lock (gtm_thread *tx);
|
|
void read_unlock (gtm_thread *tx);
|
|
|
|
void write_lock ();
|
|
void write_unlock ();
|
|
|
|
bool write_upgrade (gtm_thread *tx);
|
|
void write_upgrade_finish (gtm_thread *tx);
|
|
|
|
// Returns true iff there is a concurrent active or waiting writer, or
|
|
// htm_fastpath is zero. This is primarily useful for simple HyTM
|
|
// approaches, and the values being checked are loaded with
|
|
// memory_order_relaxed.
|
|
bool htm_fastpath_disabled ()
|
|
{
|
|
return writers.load (memory_order_relaxed) != 0
|
|
|| htm_fastpath.load (memory_order_relaxed) == 0;
|
|
}
|
|
|
|
// This does not need to return an exact value, hence relaxed MO is
|
|
// sufficient.
|
|
uint32_t get_htm_fastpath ()
|
|
{
|
|
return htm_fastpath.load (memory_order_relaxed);
|
|
}
|
|
// This must only be called while having acquired the write lock, and other
|
|
// threads do not need to load an exact value; hence relaxed MO is
|
|
// sufficient.
|
|
void set_htm_fastpath (uint32_t val)
|
|
{
|
|
htm_fastpath.store (val, memory_order_relaxed);
|
|
}
|
|
|
|
protected:
|
|
bool write_lock_generic (gtm_thread *tx);
|
|
};
|
|
|
|
} // namespace GTM
|
|
|
|
#endif // GTM_RWLOCK_H
|