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lock.jl
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lock.jl
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# This file is a part of Julia. License is MIT: https://julialang.org/license
const ThreadSynchronizer = GenericCondition{Threads.SpinLock}
# Advisory reentrant lock
"""
ReentrantLock()
Creates a re-entrant lock for synchronizing [`Task`](@ref)s. The same task can
acquire the lock as many times as required. Each [`lock`](@ref) must be matched
with an [`unlock`](@ref).
Calling 'lock' will also inhibit running of finalizers on that thread until the
corresponding 'unlock'. Use of the standard lock pattern illustrated below
should naturally be supported, but beware of inverting the try/lock order or
missing the try block entirely (e.g. attempting to return with the lock still
held):
```
lock(l)
try
<atomic work>
finally
unlock(l)
end
```
"""
mutable struct ReentrantLock <: AbstractLock
locked_by::Union{Task, Nothing}
cond_wait::ThreadSynchronizer
reentrancy_cnt::Int
ReentrantLock() = new(nothing, ThreadSynchronizer(), 0)
end
assert_havelock(l::ReentrantLock) = assert_havelock(l, l.locked_by)
"""
islocked(lock) -> Status (Boolean)
Check whether the `lock` is held by any task/thread.
This should not be used for synchronization (see instead [`trylock`](@ref)).
"""
function islocked(rl::ReentrantLock)
return rl.reentrancy_cnt != 0
end
"""
trylock(lock) -> Success (Boolean)
Acquire the lock if it is available,
and return `true` if successful.
If the lock is already locked by a different task/thread,
return `false`.
Each successful `trylock` must be matched by an [`unlock`](@ref).
"""
function trylock(rl::ReentrantLock)
t = current_task()
if t === rl.locked_by
rl.reentrancy_cnt += 1
return true
end
lock(rl.cond_wait)
if rl.reentrancy_cnt == 0
rl.locked_by = t
rl.reentrancy_cnt = 1
GC.disable_finalizers()
got = true
else
got = false
end
unlock(rl.cond_wait)
return got
end
"""
lock(lock)
Acquire the `lock` when it becomes available.
If the lock is already locked by a different task/thread,
wait for it to become available.
Each `lock` must be matched by an [`unlock`](@ref).
"""
function lock(rl::ReentrantLock)
t = current_task()
if t === rl.locked_by
rl.reentrancy_cnt += 1
else
lock(rl.cond_wait)
while true
if rl.reentrancy_cnt == 0
rl.locked_by = t
rl.reentrancy_cnt = 1
GC.disable_finalizers()
break
end
try
wait(rl.cond_wait)
catch
unlock(rl.cond_wait)
rethrow()
end
end
unlock(rl.cond_wait)
end
return
end
"""
unlock(lock)
Releases ownership of the `lock`.
If this is a recursive lock which has been acquired before, decrement an
internal counter and return immediately.
"""
function unlock(rl::ReentrantLock)
t = current_task()
n = rl.reentrancy_cnt
n == 0 && error("unlock count must match lock count")
rl.locked_by === t || error("unlock from wrong thread")
if n > 1
rl.reentrancy_cnt = n - 1
else
lock(rl.cond_wait)
rl.reentrancy_cnt = 0
rl.locked_by = nothing
if !isempty(rl.cond_wait.waitq)
try
notify(rl.cond_wait)
catch
unlock(rl.cond_wait)
rethrow()
end
end
GC.enable_finalizers()
unlock(rl.cond_wait)
end
return
end
function unlockall(rl::ReentrantLock)
t = current_task()
n = rl.reentrancy_cnt
rl.locked_by === t || error("unlock from wrong thread")
n == 0 && error("unlock count must match lock count")
lock(rl.cond_wait)
rl.reentrancy_cnt = 0
rl.locked_by = nothing
if !isempty(rl.cond_wait.waitq)
try
notify(rl.cond_wait)
catch
unlock(rl.cond_wait)
rethrow()
end
end
GC.enable_finalizers()
unlock(rl.cond_wait)
return n
end
function relockall(rl::ReentrantLock, n::Int)
t = current_task()
lock(rl)
n1 = rl.reentrancy_cnt
rl.reentrancy_cnt = n
n1 == 1 || concurrency_violation()
return
end
"""
lock(f::Function, lock)
Acquire the `lock`, execute `f` with the `lock` held, and release the `lock` when `f`
returns. If the lock is already locked by a different task/thread, wait for it to become
available.
When this function returns, the `lock` has been released, so the caller should
not attempt to `unlock` it.
"""
function lock(f, l::AbstractLock)
lock(l)
try
return f()
finally
unlock(l)
end
end
function trylock(f, l::AbstractLock)
if trylock(l)
try
return f()
finally
unlock(l)
end
end
return false
end
macro lock(l, expr)
quote
temp = $(esc(l))
lock(temp)
try
$(esc(expr))
finally
unlock(temp)
end
end
end
macro lock_nofail(l, expr)
quote
temp = $(esc(l))
lock(temp)
val = $(esc(expr))
unlock(temp)
val
end
end
@eval Threads begin
"""
Threads.Condition([lock])
A thread-safe version of [`Base.Condition`](@ref).
To call [`wait`](@ref) or [`notify`](@ref) on a `Threads.Condition`, you must first call
[`lock`](@ref) on it. When `wait` is called, the lock is atomically released during
blocking, and will be reacquired before `wait` returns. Therefore idiomatic use
of a `Threads.Condition` `c` looks like the following:
```
lock(c)
try
while !thing_we_are_waiting_for
wait(c)
end
finally
unlock(c)
end
```
!!! compat "Julia 1.2"
This functionality requires at least Julia 1.2.
"""
const Condition = Base.GenericCondition{Base.ReentrantLock}
"""
Special note for [`Threads.Condition`](@ref):
The caller must be holding the [`lock`](@ref) that owns a `Threads.Condition` before calling this method.
The calling task will be blocked until some other task wakes it,
usually by calling [`notify`](@ref) on the same `Threads.Condition` object.
The lock will be atomically released when blocking (even if it was locked recursively),
and will be reacquired before returning.
"""
wait(c::Condition)
end
"""
Semaphore(sem_size)
Create a counting semaphore that allows at most `sem_size`
acquires to be in use at any time.
Each acquire must be matched with a release.
"""
mutable struct Semaphore
sem_size::Int
curr_cnt::Int
cond_wait::Threads.Condition
Semaphore(sem_size) = sem_size > 0 ? new(sem_size, 0, Threads.Condition()) : throw(ArgumentError("Semaphore size must be > 0"))
end
"""
acquire(s::Semaphore)
Wait for one of the `sem_size` permits to be available,
blocking until one can be acquired.
"""
function acquire(s::Semaphore)
lock(s.cond_wait)
try
while s.curr_cnt >= s.sem_size
wait(s.cond_wait)
end
s.curr_cnt = s.curr_cnt + 1
finally
unlock(s.cond_wait)
end
return
end
"""
release(s::Semaphore)
Return one permit to the pool,
possibly allowing another task to acquire it
and resume execution.
"""
function release(s::Semaphore)
lock(s.cond_wait)
try
s.curr_cnt > 0 || error("release count must match acquire count")
s.curr_cnt -= 1
notify(s.cond_wait; all=false)
finally
unlock(s.cond_wait)
end
return
end
"""
Event()
Create a level-triggered event source. Tasks that call [`wait`](@ref) on an
`Event` are suspended and queued until `notify` is called on the `Event`.
After `notify` is called, the `Event` remains in a signaled state and
tasks will no longer block when waiting for it.
!!! compat "Julia 1.1"
This functionality requires at least Julia 1.1.
"""
mutable struct Event
notify::Threads.Condition
set::Bool
Event() = new(Threads.Condition(), false)
end
function wait(e::Event)
e.set && return
lock(e.notify)
try
while !e.set
wait(e.notify)
end
finally
unlock(e.notify)
end
nothing
end
function notify(e::Event)
lock(e.notify)
try
if !e.set
e.set = true
notify(e.notify)
end
finally
unlock(e.notify)
end
nothing
end
@eval Threads begin
import .Base: Event
export Event
end