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//===-- tsan_clock.cc -----------------------------------------------------===//
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file is a part of ThreadSanitizer (TSan), a race detector.
//
//===----------------------------------------------------------------------===//
#include "tsan_clock.h"
#include "tsan_rtl.h"
// It's possible to optimize clock operations for some important cases
// so that they are O(1). The cases include singletons, once's, local mutexes.
// First, SyncClock must be re-implemented to allow indexing by tid.
// It must not necessarily be a full vector clock, though. For example it may
// be a multi-level table.
// Then, each slot in SyncClock must contain a dirty bit (it's united with
// the clock value, so no space increase). The acquire algorithm looks
// as follows:
// void acquire(thr, tid, thr_clock, sync_clock) {
// if (!sync_clock[tid].dirty)
// return; // No new info to acquire.
// // This handles constant reads of singleton pointers and
// // stop-flags.
// acquire_impl(thr_clock, sync_clock); // As usual, O(N).
// sync_clock[tid].dirty = false;
// sync_clock.dirty_count--;
// }
// The release operation looks as follows:
// void release(thr, tid, thr_clock, sync_clock) {
// // thr->sync_cache is a simple fixed-size hash-based cache that holds
// // several previous sync_clock's.
// if (thr->sync_cache[sync_clock] >= thr->last_acquire_epoch) {
// // The thread did no acquire operations since last release on this clock.
// // So update only the thread's slot (other slots can't possibly change).
// sync_clock[tid].clock = thr->epoch;
// if (sync_clock.dirty_count == sync_clock.cnt
// || (sync_clock.dirty_count == sync_clock.cnt - 1
// && sync_clock[tid].dirty == false))
// // All dirty flags are set, bail out.
// return;
// set all dirty bits, but preserve the thread's bit. // O(N)
// update sync_clock.dirty_count;
// return;
// }
// release_impl(thr_clock, sync_clock); // As usual, O(N).
// set all dirty bits, but preserve the thread's bit.
// // The previous step is combined with release_impl(), so that
// // we scan the arrays only once.
// update sync_clock.dirty_count;
// }
namespace __tsan {
ThreadClock::ThreadClock() {
nclk_ = 0;
for (uptr i = 0; i < (uptr)kMaxTidInClock; i++)
clk_[i] = 0;
}
void ThreadClock::acquire(const SyncClock *src) {
DCHECK(nclk_ <= kMaxTid);
DCHECK(src->clk_.Size() <= kMaxTid);
const uptr nclk = src->clk_.Size();
if (nclk == 0)
return;
nclk_ = max(nclk_, nclk);
for (uptr i = 0; i < nclk; i++) {
if (clk_[i] < src->clk_[i])
clk_[i] = src->clk_[i];
}
}
void ThreadClock::release(SyncClock *dst) const {
DCHECK(nclk_ <= kMaxTid);
DCHECK(dst->clk_.Size() <= kMaxTid);
if (dst->clk_.Size() < nclk_)
dst->clk_.Resize(nclk_);
for (uptr i = 0; i < nclk_; i++) {
if (dst->clk_[i] < clk_[i])
dst->clk_[i] = clk_[i];
}
}
void ThreadClock::ReleaseStore(SyncClock *dst) const {
DCHECK(nclk_ <= kMaxTid);
DCHECK(dst->clk_.Size() <= kMaxTid);
if (dst->clk_.Size() < nclk_)
dst->clk_.Resize(nclk_);
for (uptr i = 0; i < nclk_; i++)
dst->clk_[i] = clk_[i];
for (uptr i = nclk_; i < dst->clk_.Size(); i++)
dst->clk_[i] = 0;
}
void ThreadClock::acq_rel(SyncClock *dst) {
acquire(dst);
release(dst);
}
SyncClock::SyncClock()
: clk_(MBlockClock) {
}
} // namespace __tsan
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