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/**
* SpinLock for runtime internal usage.
*
* Copyright: Copyright Digital Mars 2015 -.
* License: $(WEB www.boost.org/LICENSE_1_0.txt, Boost License 1.0).
* Authors: Martin Nowak
* Source: $(DRUNTIMESRC core/internal/_spinlock.d)
*/
module core.internal.spinlock;
import core.atomic, core.thread;
shared struct SpinLock
{
/// for how long is the lock usually contended
enum Contention : ubyte
{
brief,
medium,
lengthy,
}
@trusted @nogc nothrow:
this(Contention contention)
{
this.contention = contention;
}
void lock()
{
if (cas(&val, size_t(0), size_t(1)))
return;
// Try to reduce the chance of another cas failure
// TTAS lock (https://en.wikipedia.org/wiki/Test_and_test-and-set)
immutable step = 1 << contention;
while (true)
{
for (size_t n; atomicLoad!(MemoryOrder.raw)(val); n += step)
yield(n);
if (cas(&val, size_t(0), size_t(1)))
return;
}
}
void unlock()
{
atomicStore!(MemoryOrder.rel)(val, size_t(0));
}
/// yield with backoff
void yield(size_t k)
{
if (k < pauseThresh)
return pause();
else if (k < 32)
return Thread.yield();
Thread.sleep(1.msecs);
}
private:
version (D_InlineAsm_X86)
enum X86 = true;
else version (D_InlineAsm_X86_64)
enum X86 = true;
else
enum X86 = false;
static if (X86)
{
enum pauseThresh = 16;
void pause()
{
asm @trusted @nogc nothrow
{
// pause instruction
rep;
nop;
}
}
}
else
{
enum pauseThresh = 4;
void pause()
{
}
}
size_t val;
Contention contention;
}
// aligned to cacheline to avoid false sharing
shared align(64) struct AlignedSpinLock
{
this(SpinLock.Contention contention)
{
impl = shared(SpinLock)(contention);
}
SpinLock impl;
alias impl this;
}
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