# I get a dead lock with only one lock
**URL:** https://discourse.julialang.org/t/i-get-a-dead-lock-with-only-one-lock/78788
**Category:** General Usage
**Created:** [March 31, 2022, 8:50am UTC](https://discourse.julialang.org/t/i-get-a-dead-lock-with-only-one-lock/78788 "2022-03-31T08:50:09Z")
**Posts on this page:** 16
**Page:** 1
### Author:  [@Impressium](https://discourse.julialang.org/u/Impressium)
#### Post date: [March 31, 2022, 8:50am UTC](https://discourse.julialang.org/t/i-get-a-dead-lock-with-only-one-lock/78788/1 "2022-03-31T08:50:09Z")
Hi all 🙂
I’ve got the following in one of my pkgs. I put a print before and after. But one in 100 run it just stops there and does not print the second time. I’m kinda clueless how to debug this problem even more and fix it. Seems like correct Julia code for me. (PS: I don’t get the issue with the example code in the repl)
```julia
julia> l = ReentrantLock()
ReentrantLock(nothing, Base.GenericCondition{Base.Threads.SpinLock}(Base.InvasiveLinkedList{Task}(nothing, nothing), Base.Threads.SpinLock(0)), 0)
julia> d = Dict()
Dict{Any, Any}()
julia> lock(l) do
d[:key] = :value
end
:value
```
Cheers
Edit:
Julia Version 1.6.3 and 1.7.2
---
### Author:  [@lawless-m](https://discourse.julialang.org/u/lawless-m)
#### Post date: [March 31, 2022, 8:55am UTC](https://discourse.julialang.org/t/i-get-a-dead-lock-with-only-one-lock/78788/2 "2022-03-31T08:55:45Z")
bit hard to help when your MWE works just fine 🙂
even this without deadlock
```julia
for i in 1:1_000_000
lock(l) do
print("a");
d[:key] = :value
end
end
```
---
### Author:  [@goerch](https://discourse.julialang.org/u/goerch)
#### Post date: [March 31, 2022, 8:55am UTC](https://discourse.julialang.org/t/i-get-a-dead-lock-with-only-one-lock/78788/3 "2022-03-31T08:55:59Z")
Your example looks like serial code. Why use a lock then in the first place?
---
### Author:  [@Impressium](https://discourse.julialang.org/u/Impressium)
#### Post date: [March 31, 2022, 9:04am UTC](https://discourse.julialang.org/t/i-get-a-dead-lock-with-only-one-lock/78788/4 "2022-03-31T09:04:35Z")
```julia
Base.@kwdef struct _ActiveBars
dict::Dict{Int, BarManager} = Dict{Int, BarManager}()
last_id::Threads.Atomic{Int} = Threads.Atomic{Int}(1)
lock::ReentrantLock = ReentrantLock()
end
const _ACTIVE_BARS = _ActiveBars()
function _start(;
bar_structure::Type{BarStructureType},
initial_bars::Union{Vector{Dict{UniqueSymbol{ExchangeSymbolType},BarStructureType}}, Nothing},
interval_between_bars::Second,
bar_calculation::Function,
unique_symbols::Set{UniqueSymbol{ExchangeSymbolType}},
quote_change_types::Vector{Messages.QuoteChangeTypes.QuoteChangeType},
bar_output::Function,
include_with_these_last_trade_conditioncodes::Vector{String},
drop_message::Function,
history_length::Int,
future_length::Int,
active_bars::_ActiveBars = _ACTIVE_BARS
)::Int where {BarStructureType, ExchangeSymbolType <: AbstractExchangeSymbol}
id = Threads.atomic_add!(active_bars.last_id, 1)
bar_manager = BarManager{BarStructureType, ExchangeSymbolType}(;
name = "bar_$id",
bar_output,
bar_calculation,
unique_symbols,
quote_change_types,
initial_bars,
interval_between_bars,
include_with_these_last_trade_conditioncodes,
drop_message,
history_length,
future_length,
)
_start(bar_manager)
lock(active_bars.lock) do
active_bars.dict[id] = bar_manager
end
return id
end
function _stop(
id::Int;
active_bars::_ActiveBars = _ACTIVE_BARS
)::Nothing
bar_manager = lock(active_bars.lock) do
pop!(
active_bars.dict,
id,
nothing
)
end
isnothing(bar_manager) && error()
_stop(bar_manager)
return
end
```
That’s the code. I want to make sure that start and stop can be called from different threads… That’s why I use the lock
---
### Author:  [@Impressium](https://discourse.julialang.org/u/Impressium)
#### Post date: [March 31, 2022, 9:05am UTC](https://discourse.julialang.org/t/i-get-a-dead-lock-with-only-one-lock/78788/5 "2022-03-31T09:05:39Z")
The example problem works for me as well… That’s the problem
---
### Author:  [@Impressium](https://discourse.julialang.org/u/Impressium)
#### Post date: [March 31, 2022, 9:06am UTC](https://discourse.julialang.org/t/i-get-a-dead-lock-with-only-one-lock/78788/6 "2022-03-31T09:06:28Z")
That’s just the example. I want to make sure that start and stop are thread safe
---
### Author:  [@goerch](https://discourse.julialang.org/u/goerch)
#### Post date: [March 31, 2022, 9:16am UTC](https://discourse.julialang.org/t/i-get-a-dead-lock-with-only-one-lock/78788/7 "2022-03-31T09:16:30Z")
Depending on the number of `_ActiveBars` instances floating around you could have more than one lock?
To verify if locking is really the problem here you could use `Base.trylock`?
---
### Author:  [@Impressium](https://discourse.julialang.org/u/Impressium)
#### Post date: [March 31, 2022, 9:32am UTC](https://discourse.julialang.org/t/i-get-a-dead-lock-with-only-one-lock/78788/8 "2022-03-31T09:32:19Z")
Should only be one. Because of the const in front of it
---
### Author:  [@Sukera](https://discourse.julialang.org/u/Sukera)
#### Post date: [March 31, 2022, 9:40am UTC](https://discourse.julialang.org/t/i-get-a-dead-lock-with-only-one-lock/78788/9 "2022-03-31T09:40:51Z")
> [@Impressium](#):
>
> `_start(bar_manager)`
What does this ultimately call? As far as I can tell, it’s not part of the code you posted.
---
### Author:  [@Impressium](https://discourse.julialang.org/u/Impressium)
#### Post date: [March 31, 2022, 10:16am UTC](https://discourse.julialang.org/t/i-get-a-dead-lock-with-only-one-lock/78788/10 "2022-03-31T10:16:07Z")
```julia
function _start(bar_manager::BarManager)::Nothing
bar_manager.is_running[] = true
_HistoryManagement.start(bar_manager.history)
bar_manager.market_subscribtion_id[] = Markets.subscribe(
(message) -> _HistoryManagement.getting_messages(bar_manager.history, message),
[
Markets.SymbolSubscriptionInfo(;
unique_symbol = unique_symbol,
quote_change_types = bar_manager.history.quote_change_types
)
for unique_symbol in bar_manager.history.unique_symbols |> values
]
)
bar_manager.producing_task[] = Utils.@my_spawn _start_producing_bars!(bar_manager)
return
end
```
---
### Author:  [@goerch](https://discourse.julialang.org/u/goerch)
#### Post date: [March 31, 2022, 10:47am UTC](https://discourse.julialang.org/t/i-get-a-dead-lock-with-only-one-lock/78788/11 "2022-03-31T10:47:54Z")
> [@Impressium](#):
>
> I put a print before and after. But one in 100 run it just stops there and does not print the second time. I’m kinda clueless how to debug this problem even more and fix it.
Here is what I would try assuming a problem in my code(and it would be a pain in the …): first I’d try to make the problem more reproducible mainly increasing the CPU workload artificially (eliminating file I/O and network I/O, increasing number of threads etc.). Then I’d try to produce a trace of the multi threading activity (spawns, joins, locks, channel read/write). With a bit of luck one of these traces could reveal a deadlock…
There could be chance that you are encountering a [Julia problem](https://github.com/JuliaLang/julia/search?q=deadlock&type=issues), but even in this case the steps above could help finding a reproducer…
---
### Author:  [@Impressium](https://discourse.julialang.org/u/Impressium)
#### Post date: [March 31, 2022, 10:54am UTC](https://discourse.julialang.org/t/i-get-a-dead-lock-with-only-one-lock/78788/12 "2022-03-31T10:54:41Z")
I tried it now with `Base.trylock`. Same behavior - one in 100 stops
---
### Author:  [@goerch](https://discourse.julialang.org/u/goerch)
#### Post date: [March 31, 2022, 11:04am UTC](https://discourse.julialang.org/t/i-get-a-dead-lock-with-only-one-lock/78788/13 "2022-03-31T11:04:17Z")
> [@Impressium](#):
>
> I tried it now with `Base.trylock` . Same behavior - one in 100 stops
But `trylock` doesn’t wait: it returns `false` if the lock is not available.
---
### Author:  [@Impressium](https://discourse.julialang.org/u/Impressium)
#### Post date: [March 31, 2022, 11:08am UTC](https://discourse.julialang.org/t/i-get-a-dead-lock-with-only-one-lock/78788/14 "2022-03-31T11:08:01Z")
The strange part about it. Maybe I did something wrong.
```julia
if Base.trylock(active_bars.lock)
active_bars.dict[id] = bar_manager
unlock(active_bars.lock)
else
error("Not able to lock")
end
# lock(active_bars.lock) do
# active_bars.dict[id] = bar_manager
# end
```
---
### Author:  [@goerch](https://discourse.julialang.org/u/goerch)
#### Post date: [March 31, 2022, 12:45pm UTC](https://discourse.julialang.org/t/i-get-a-dead-lock-with-only-one-lock/78788/15 "2022-03-31T12:45:09Z")
> [@Impressium](#):
>
> Maybe I did something wrong.
No, I’d extend it to something like
```julia
l = ReentrantLock()
retries = 5
while retries > 0
if Base.trylock(l)
unlock(l)
break
end
sleep(1)
@info "retrying"
retries -= 1
end
if retries == 0
@error "deadlock?"
end
```
Couple of more questions:
- do you see any Julia activity in your system monitor when the problem occurs?
- did you check with different Julia versions?
---
### Author:  [@Impressium](https://discourse.julialang.org/u/Impressium)
#### Post date: [March 31, 2022, 6:13pm UTC](https://discourse.julialang.org/t/i-get-a-dead-lock-with-only-one-lock/78788/16 "2022-03-31T18:13:44Z")
Quick update… it wasn’t the lock, but the `start` function bevor. But still don’t know why it’s stops completely…
Thank you all