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| //===-- tsd_shared.h --------------------------------------------*- C++ -*-===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
#ifndef SCUDO_TSD_SHARED_H_
#define SCUDO_TSD_SHARED_H_
#include "linux.h" // for getAndroidTlsPtr()
#include "tsd.h"
#include <pthread.h>
namespace scudo {
template <class Allocator, u32 MaxTSDCount> struct TSDRegistrySharedT {
void initLinkerInitialized(Allocator *Instance) {
Instance->initLinkerInitialized();
CHECK_EQ(pthread_key_create(&PThreadKey, nullptr), 0); // For non-TLS
NumberOfTSDs = Min(Max(1U, getNumberOfCPUs()), MaxTSDCount);
TSDs = reinterpret_cast<TSD<Allocator> *>(
map(nullptr, sizeof(TSD<Allocator>) * NumberOfTSDs, "scudo:tsd"));
for (u32 I = 0; I < NumberOfTSDs; I++)
TSDs[I].initLinkerInitialized(Instance);
// Compute all the coprimes of NumberOfTSDs. This will be used to walk the
// array of TSDs in a random order. For details, see:
// https://lemire.me/blog/2017/09/18/visiting-all-values-in-an-array-exactly-once-in-random-order/
for (u32 I = 0; I < NumberOfTSDs; I++) {
u32 A = I + 1;
u32 B = NumberOfTSDs;
// Find the GCD between I + 1 and NumberOfTSDs. If 1, they are coprimes.
while (B != 0) {
const u32 T = A;
A = B;
B = T % B;
}
if (A == 1)
CoPrimes[NumberOfCoPrimes++] = I + 1;
}
Initialized = true;
}
void init(Allocator *Instance) {
memset(this, 0, sizeof(*this));
initLinkerInitialized(Instance);
}
void unmapTestOnly() {
unmap(reinterpret_cast<void *>(TSDs),
sizeof(TSD<Allocator>) * NumberOfTSDs);
}
ALWAYS_INLINE void initThreadMaybe(Allocator *Instance,
UNUSED bool MinimalInit) {
if (LIKELY(getCurrentTSD()))
return;
initThread(Instance);
}
ALWAYS_INLINE TSD<Allocator> *getTSDAndLock(bool *UnlockRequired) {
TSD<Allocator> *TSD = getCurrentTSD();
DCHECK(TSD);
*UnlockRequired = true;
// Try to lock the currently associated context.
if (TSD->tryLock())
return TSD;
// If that fails, go down the slow path.
return getTSDAndLockSlow(TSD);
}
private:
ALWAYS_INLINE void setCurrentTSD(TSD<Allocator> *CurrentTSD) {
#if SCUDO_ANDROID
*getAndroidTlsPtr() = reinterpret_cast<uptr>(CurrentTSD);
#elif SCUDO_LINUX
ThreadTSD = CurrentTSD;
#else
CHECK_EQ(
pthread_setspecific(PThreadKey, reinterpret_cast<void *>(CurrentTSD)),
0);
#endif
}
ALWAYS_INLINE TSD<Allocator> *getCurrentTSD() {
#if SCUDO_ANDROID
return reinterpret_cast<TSD<Allocator> *>(*getAndroidTlsPtr());
#elif SCUDO_LINUX
return ThreadTSD;
#else
return reinterpret_cast<TSD<Allocator> *>(pthread_getspecific(PThreadKey));
#endif
}
void initOnceMaybe(Allocator *Instance) {
ScopedLock L(Mutex);
if (LIKELY(Initialized))
return;
initLinkerInitialized(Instance); // Sets Initialized.
}
NOINLINE void initThread(Allocator *Instance) {
initOnceMaybe(Instance);
// Initial context assignment is done in a plain round-robin fashion.
const u32 Index = atomic_fetch_add(&CurrentIndex, 1U, memory_order_relaxed);
setCurrentTSD(&TSDs[Index % NumberOfTSDs]);
}
NOINLINE TSD<Allocator> *getTSDAndLockSlow(TSD<Allocator> *CurrentTSD) {
if (MaxTSDCount > 1U && NumberOfTSDs > 1U) {
// Use the Precedence of the current TSD as our random seed. Since we are
// in the slow path, it means that tryLock failed, and as a result it's
// very likely that said Precedence is non-zero.
const u32 R = static_cast<u32>(CurrentTSD->getPrecedence());
const u32 Inc = CoPrimes[R % NumberOfCoPrimes];
u32 Index = R % NumberOfTSDs;
uptr LowestPrecedence = UINTPTR_MAX;
TSD<Allocator> *CandidateTSD = nullptr;
// Go randomly through at most 4 contexts and find a candidate.
for (u32 I = 0; I < Min(4U, NumberOfTSDs); I++) {
if (TSDs[Index].tryLock()) {
setCurrentTSD(&TSDs[Index]);
return &TSDs[Index];
}
const uptr Precedence = TSDs[Index].getPrecedence();
// A 0 precedence here means another thread just locked this TSD.
if (Precedence && Precedence < LowestPrecedence) {
CandidateTSD = &TSDs[Index];
LowestPrecedence = Precedence;
}
Index += Inc;
if (Index >= NumberOfTSDs)
Index -= NumberOfTSDs;
}
if (CandidateTSD) {
CandidateTSD->lock();
setCurrentTSD(CandidateTSD);
return CandidateTSD;
}
}
// Last resort, stick with the current one.
CurrentTSD->lock();
return CurrentTSD;
}
pthread_key_t PThreadKey;
atomic_u32 CurrentIndex;
u32 NumberOfTSDs;
TSD<Allocator> *TSDs;
u32 NumberOfCoPrimes;
u32 CoPrimes[MaxTSDCount];
bool Initialized;
HybridMutex Mutex;
#if SCUDO_LINUX && !SCUDO_ANDROID
static THREADLOCAL TSD<Allocator> *ThreadTSD;
#endif
};
#if SCUDO_LINUX && !SCUDO_ANDROID
template <class Allocator, u32 MaxTSDCount>
THREADLOCAL TSD<Allocator>
*TSDRegistrySharedT<Allocator, MaxTSDCount>::ThreadTSD;
#endif
} // namespace scudo
#endif // SCUDO_TSD_SHARED_H_
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