locks-mt.jl
# This file is a part of Julia. License is MIT: https://julialang.org/license
import .Base: unsafe_convert, lock, trylock, unlock, islocked, wait, notify, AbstractLock
# Important Note: these low-level primitives defined here
# are typically not for general usage
##########################################
# Atomic Locks
##########################################
# 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.
"""
SpinLock()
Create a non-reentrant lock.
Recursive use will result in a deadlock.
Each [`lock`](@ref) must be matched with an [`unlock`](@ref).
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 [`Mutex`](@ref) for a more efficient version on one core or if the
lock may be held for a considerable length of time.
"""
struct SpinLock <: AbstractLock
handle::Atomic{Int}
SpinLock() = new(Atomic{Int}(0))
end
function lock(l::SpinLock)
while true
if l.handle[] == 0
p = atomic_xchg!(l.handle, 1)
if p == 0
return
end
end
ccall(:jl_cpu_pause, Cvoid, ())
# Temporary solution before we have gc transition support in codegen.
ccall(:jl_gc_safepoint, Cvoid, ())
end
end
function trylock(l::SpinLock)
if l.handle[] == 0
return atomic_xchg!(l.handle, 1) == 0
end
return false
end
function unlock(l::SpinLock)
l.handle[] = 0
ccall(:jl_cpu_wake, Cvoid, ())
return
end
function islocked(l::SpinLock)
return l.handle[] != 0
end
##########################################
# System Mutexes
##########################################
# These are mutexes from libuv.
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`](@ref) for a lighter-weight lock.
"""
mutable struct Mutex <: AbstractLock
ownertid::Int16
handle::Ptr{Cvoid}
function Mutex()
m = new(zero(Int16), Libc.malloc(UV_MUTEX_SIZE))
ccall(:uv_mutex_init, Cvoid, (Ptr{Cvoid},), m.handle)
finalizer(mutex_destroy, m)
return m
end
end
unsafe_convert(::Type{Ptr{Cvoid}}, m::Mutex) = m.handle
function mutex_destroy(x::Mutex)
h = x.handle
if h != C_NULL
x.handle = C_NULL
ccall(:uv_mutex_destroy, Cvoid, (Ptr{Cvoid},), h)
Libc.free(h)
nothing
end
end
function lock(m::Mutex)
m.ownertid == threadid() && concurrency_violation() # deadlock
# 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, Cvoid, (Ptr{Cvoid},), m)
ccall(:jl_gc_safe_leave, Cvoid, (Int8,), gc_state)
m.ownertid = threadid()
return
end
function trylock(m::Mutex)
m.ownertid == threadid() && concurrency_violation() # deadlock
r = ccall(:uv_mutex_trylock, Cint, (Ptr{Cvoid},), m)
if r == 0
m.ownertid = threadid()
end
return r == 0
end
function unlock(m::Mutex)
m.ownertid == threadid() || concurrency_violation()
m.ownertid = 0
ccall(:uv_mutex_unlock, Cvoid, (Ptr{Cvoid},), m)
return
end
function islocked(m::Mutex)
return m.ownertid != 0
end