Generator threw java.lang.NullPointerException - nil when asked for an operation.

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Anton Kaliaev

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Feb 10, 2021, 8:24:36 AM2/10/21

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Hi,

Sorry for bothering you again, but maybe you can help me understand why my generator throws java.lang.NullPointerException.

(defrecord Generator []

gen/Generator

(op [this test ctx]

(info "refreshing config")

(let [config (refresh-config! test)]

(info :config-refreshed)

(info (with-out-str (pprint config)))

(info (with-out-str (pprint (compact-config config))))

[{:f :transition

:value {:value {:validator {:address "A14125126B7862E1930DBEE7DE54F8F05C7E75A4", :priv_key {:value "McmfghDYydfemxILvXmPGSAnUDfddMTyXSbsVPTzpr0zfPPRAJNFXRrwNvDawaH/4vo9XjO1chNo8JQo8wgjkw==", :type "tendermint/PrivKeyEd25519"}, :pub_key {:value "M3zz0QCTRV0a8Dbw2sGh/+L6PV4ztXITaPCUKPMII5M=", :type "tendermint/PubKeyEd25519"}, :votes 2}, :type :add, :version 0}, :f :transition}} this])

)

(update [this test ctx event]

this))

https://github.com/tendermint/jepsen/blob/main/tendermint/src/jepsen/tendermint/validator.clj#L961-L977

Running this fails with:

clojure.lang.ExceptionInfo: Generator threw java.lang.NullPointerException - nil when asked for an operation. Generator:

(jepsen.generator.Synchronize{

:gen jepsen.generator.TimeLimit{

:limit 60000000000,

:cutoff nil,

:gen jepsen.generator.Any{

:gens [jepsen.generator.OnThreads{

:f #{:nemesis},

:gen jepsen.generator.Stagger{

:dt 2000000000,

:next-time nil,

:gen jepsen.tendermint.validator.Generator{

}}}

jepsen.generator.OnThreads{

:f #object[clojure.core$complement$fn__5669 0x25be3c66 "clojure.core$complement$fn__5669@25be3c66"],

:gen jepsen.generator.OnThreads{

:f #object[clojure.core$complement$fn__5669 0x1e07ae6 "clojure.core$complement$fn__5669@1e07ae6"],

:gen jepsen.independent.ConcurrentGenerator{

:n 10,

:fgen #object[jepsen.tendermint.core$workload$fn__28878 0x6baf95f9 "jepsen.tendermint.core$workload$fn__28878@6baf95f9"],

:group->threads nil,

:thread->group nil,

:keys (0 1 2 3 4 5 6 7 8 9 ...),

:gens nil}}}]}}}

jepsen.generator.Synchronize{

:gen jepsen.generator.OnThreads{

:f #{:nemesis},

:gen jepsen.generator.Limit{

:remaining 1, :gen {:type :info, :f :stop}}}}

jepsen.generator.Synchronize{

:gen {:type :sleep, :value 30}}

jepsen.generator.Synchronize{

:gen jepsen.generator.OnThreads{

:f #object[clojure.core$complement$fn__5669 0x29063116 "clojure.core$complement$fn__5669@29063116"],

:gen nil}})

Context:

{:time 172476900,

:free-threads

#object[io.lacuna.bifurcan.Set 0x20f6e126 "{0, 1, 2, 3, 4, 6, 7, 8, 9, 5, :nemesis}"],

:workers

{0 0, 7 7, 1 1, 4 4, 6 6, :nemesis :nemesis, 3 3, 2 2, 9 9, 5 5, 8 8}}

at slingshot.support$stack_trace.invoke(support.clj:201)

at jepsen.generator.FriendlyExceptions.op(generator.clj:681)

at jepsen.generator.Validate.op(generator.clj:621)

at jepsen.generator.interpreter$run_BANG_.invokeStatic(interpreter.clj:248)

at jepsen.generator.interpreter$run_BANG_.invoke(interpreter.clj:181)

at jepsen.core$run_case_BANG_.invokeStatic(core.clj:221)

at jepsen.core$run_case_BANG_.invoke(core.clj:213)

at jepsen.core$run_BANG_$fn__9768$fn__9775.invoke(core.clj:366)

at jepsen.core$run_BANG_$fn__9768.invoke(core.clj:363)

at jepsen.core$run_BANG_.invokeStatic(core.clj:349)

at jepsen.core$run_BANG_.invoke(core.clj:276)

at jepsen.cli$single_test_cmd$fn__10529.invoke(cli.clj:382)

at jepsen.cli$run_BANG_.invokeStatic(cli.clj:317)

at jepsen.cli$run_BANG_.invoke(cli.clj:246)

at jepsen.tendermint.cli$_main.invokeStatic(cli.clj:23)

at jepsen.tendermint.cli$_main.doInvoke(cli.clj:21)

at clojure.lang.RestFn.invoke(RestFn.java:482)

at clojure.lang.Var.invoke(Var.java:406)

at user$eval998.invokeStatic(form-init5868775686360460075.clj:1)

at user$eval998.invoke(form-init5868775686360460075.clj:1)

at clojure.lang.Compiler.eval(Compiler.java:7177)

at clojure.lang.Compiler.eval(Compiler.java:7167)

at clojure.lang.Compiler.load(Compiler.java:7636)

at clojure.lang.Compiler.loadFile(Compiler.java:7574)

at clojure.main$load_script.invokeStatic(main.clj:475)

at clojure.main$init_opt.invokeStatic(main.clj:477)

at clojure.main$init_opt.invoke(main.clj:477)

at clojure.main$initialize.invokeStatic(main.clj:508)

at clojure.main$null_opt.invokeStatic(main.clj:542)

at clojure.main$null_opt.invoke(main.clj:539)

at clojure.main$main.invokeStatic(main.clj:664)

at clojure.main$main.doInvoke(main.clj:616)

at clojure.lang.RestFn.applyTo(RestFn.java:137)

at clojure.lang.Var.applyTo(Var.java:705)

at clojure.main.main(main.java:40)

Caused by: java.lang.NullPointerException: null

at clojure.lang.Numbers.ops(Numbers.java:1068)

at clojure.lang.Numbers.lte(Numbers.java:255)

at jepsen.generator.Stagger.op(generator.clj:1271)

at jepsen.generator.OnThreads.op(generator.clj:864)

at jepsen.generator.Any$fn__3875.invoke(generator.clj:933)

at clojure.core$map_indexed$mapi__8548$fn__8549.invoke(core.clj:7308)

at clojure.lang.LazySeq.sval(LazySeq.java:42)

at clojure.lang.LazySeq.seq(LazySeq.java:51)

at clojure.lang.RT.seq(RT.java:535)

at clojure.core$seq__5402.invokeStatic(core.clj:137)

at clojure.core.protocols$seq_reduce.invokeStatic(protocols.clj:24)

at clojure.core.protocols$fn__8146.invokeStatic(protocols.clj:75)

at clojure.core.protocols$fn__8146.invoke(protocols.clj:75)

at clojure.core.protocols$fn__8088$G__8083__8101.invoke(protocols.clj:13)

at clojure.core$reduce.invokeStatic(core.clj:6828)

at clojure.core$reduce.invoke(core.clj:6810)

at jepsen.generator.Any.op(generator.clj:937)

at jepsen.generator.TimeLimit.op(generator.clj:1238)

at jepsen.generator.Synchronize.op(generator.clj:1384)

at jepsen.generator$fn__3563.invokeStatic(generator.clj:577)

at jepsen.generator$fn__3563.invoke(generator.clj:541)

at jepsen.generator$fn__3498$G__3476__3507.invoke(generator.clj:382)

at jepsen.generator.FriendlyExceptions.op(generator.clj:678)

... 33 common frames omitted

According to the docs, op function should return [op gen] pair or nil or :pending. Now, when I change the above generator to return nil

(defrecord Generator []

gen/Generator

(op [this test ctx]

(info "refreshing config")

(let [config (refresh-config! test)]

(info :config-refreshed)

(info (with-out-str (pprint config)))

(info (with-out-str (pprint (compact-config config))))

nil)

)

(update [this test ctx event]

this))

everything works fine. The question is whenever you see anything immediately wrong with:

[{:f :transition

I'm a bit confused as I don't see any source for NullPointerException as {:f :transition, ...} is simply a map. Thank you! 🙏

Kyle Kingsbury

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Feb 10, 2021, 8:31:06 AM2/10/21

to ta...@jepsen.io

Caused by: java.lang.NullPointerException: null

at clojure.lang.Numbers.ops(Numbers.java:1068)

at clojure.lang.Numbers.lte(Numbers.java:255)

at jepsen.generator.Stagger.op(generator.clj:1271)

Bet you dollars to donuts this is because your generator produces events without a :time field. Try wrapping your generator in (gen/validate); might give you some hints.

--Kyle

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Anton Kaliaev

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Feb 11, 2021, 2:50:56 AM2/11/21

to Jepsen Talk, ap...@jepsen.io

Indeed! thanks 🙏

Maybe a stupid question, but, IF gen/validate is so useful, why not wrap all generators with it by default? Or checking each op is too expensive?