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locks.jl
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locks.jl
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# This file is a part of Julia. License is MIT: https://julialang.org/license
import Base: _uv_hook_close, unsafe_convert,
lock, trylock, unlock, islocked
export SpinLock, RecursiveSpinLock, Mutex
##########################################
# Atomic Locks
##########################################
"""
AbstractLock
Abstract supertype describing types that
implement the thread-safe synchronization primitives:
`lock`, `trylock`, `unlock`, and `islocked`
"""
abstract type AbstractLock end
# Test-and-test-and-set spin locks are quickest up to about 30ish
# contending threads. If you have more contention than that, perhaps
# a lock is the wrong way to synchronize.
"""
TatasLock()
See SpinLock.
"""
struct TatasLock <: AbstractLock
handle::Atomic{Int}
TatasLock() = new(Atomic{Int}(0))
end
"""
SpinLock()
Creates a non-reentrant lock.
Recursive use will result in a deadlock.
Each `lock` must be matched with an `unlock`.
Test-and-test-and-set spin locks are quickest up to about 30ish
contending threads. If you have more contention than that, perhaps
a lock is the wrong way to synchronize.
See also RecursiveSpinLock for a version that permits recursion.
See also Mutex for a more efficient version on one core or if the lock may be held for a considerable length of time.
"""
const SpinLock = TatasLock
function lock(l::TatasLock)
while true
if l.handle[] == 0
p = atomic_xchg!(l.handle, 1)
if p == 0
return
end
end
ccall(:jl_cpu_pause, Void, ())
# Temporary solution before we have gc transition support in codegen.
ccall(:jl_gc_safepoint, Void, ())
end
end
function trylock(l::TatasLock)
if l.handle[] == 0
return atomic_xchg!(l.handle, 1) == 0
end
return false
end
function unlock(l::TatasLock)
l.handle[] = 0
ccall(:jl_cpu_wake, Void, ())
return
end
function islocked(l::TatasLock)
return l.handle[] != 0
end
"""
RecursiveTatasLock()
See RecursiveSpinLock.
"""
struct RecursiveTatasLock <: AbstractLock
ownertid::Atomic{Int16}
handle::Atomic{Int}
RecursiveTatasLock() = new(Atomic{Int16}(0), Atomic{Int}(0))
end
"""
RecursiveSpinLock()
Creates a reentrant lock.
The same thread can acquire the lock as many times as required.
Each `lock` must be matched with an `unlock`.
See also SpinLock for a slightly faster version.
See also Mutex for a more efficient version on one core or if the lock may be held for a considerable length of time.
"""
const RecursiveSpinLock = RecursiveTatasLock
function lock(l::RecursiveTatasLock)
if l.ownertid[] == threadid()
l.handle[] += 1
return
end
while true
if l.handle[] == 0
if atomic_cas!(l.handle, 0, 1) == 0
l.ownertid[] = threadid()
return
end
end
ccall(:jl_cpu_pause, Void, ())
# Temporary solution before we have gc transition support in codegen.
ccall(:jl_gc_safepoint, Void, ())
end
end
function trylock(l::RecursiveTatasLock)
if l.ownertid[] == threadid()
l.handle[] += 1
return true
end
if l.handle[] == 0
if atomic_cas!(l.handle, 0, 1) == 0
l.ownertid[] = threadid()
return true
end
return false
end
return false
end
function unlock(l::RecursiveTatasLock)
@assert(l.ownertid[] == threadid(), "unlock from wrong thread")
@assert(l.handle[] != 0, "unlock count must match lock count")
if l.handle[] == 1
l.ownertid[] = 0
l.handle[] = 0
ccall(:jl_cpu_wake, Void, ())
else
l.handle[] -= 1
end
return
end
function islocked(l::RecursiveTatasLock)
return l.handle[] != 0
end
##########################################
# System Mutexes
##########################################
# These are mutexes from libuv. We're doing some error checking (and
# paying for it in overhead), but regardless, in some situations,
# passing a bad parameter will cause an abort.
# TODO: how defensive to get, and how to turn it off?
# TODO: how to catch an abort?
const UV_MUTEX_SIZE = ccall(:jl_sizeof_uv_mutex, Cint, ())
"""
Mutex()
These are standard system mutexes for locking critical sections of logic.
On Windows, this is a critical section object,
on pthreads, this is a `pthread_mutex_t`.
See also SpinLock for a lighter-weight lock.
"""
mutable struct Mutex <: AbstractLock
ownertid::Int16
handle::Ptr{Void}
function Mutex()
m = new(zero(Int16), Libc.malloc(UV_MUTEX_SIZE))
ccall(:uv_mutex_init, Void, (Ptr{Void},), m.handle)
finalizer(m, _uv_hook_close)
return m
end
end
unsafe_convert(::Type{Ptr{Void}}, m::Mutex) = m.handle
function _uv_hook_close(x::Mutex)
h = x.handle
if h != C_NULL
x.handle = C_NULL
ccall(:uv_mutex_destroy, Void, (Ptr{Void},), h)
Libc.free(h)
nothing
end
end
function lock(m::Mutex)
if m.ownertid == threadid()
return
end
# Temporary solution before we have gc transition support in codegen.
# This could mess up gc state when we add codegen support.
gc_state = ccall(:jl_gc_safe_enter, Int8, ())
ccall(:uv_mutex_lock, Void, (Ptr{Void},), m)
ccall(:jl_gc_safe_leave, Void, (Int8,), gc_state)
m.ownertid = threadid()
return
end
function trylock(m::Mutex)
if m.ownertid == threadid()
return true
end
r = ccall(:uv_mutex_trylock, Cint, (Ptr{Void},), m)
if r == 0
m.ownertid = threadid()
end
return r == 0
end
function unlock(m::Mutex)
@assert(m.ownertid == threadid(), "unlock from wrong thread")
m.ownertid = 0
ccall(:uv_mutex_unlock, Void, (Ptr{Void},), m)
return
end
function islocked(m::Mutex)
return m.ownertid != 0
end