fread fails when warning is caught: "Previous fread() session was not cleaned up properly. Cleaned up ok at the beginning of this fread() call"

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Assessment

Difficulty
3/5
Estimated time
1-2 days
Newbie friendliness
35/100
Issue type
Bug
Clarity
Mostly clear
Activity status
Stale
Tech stack
r
Domain
data

Research direction

Reproduce the warning with the supplied fread() calls and tryCatch block, using the reported data.table 1.11.2 context if available. Start at the fread() entry point and trace cleanup after a caught warning. Done means the final fread() call no longer emits the spurious cleanup warning while the original warning remains handled.

Written by the indexing model from the issue text.

Description

bug fread

The three lines below work as expected:

fread("will, work\njust, fine\nthank, you", header = FALSE, sep=",", sep2=",")
fread("fails, rather\nbadly, too\nbad", header = FALSE, sep=",", sep2=",")
fread("will, work\njust, fine\nthank, you", header = FALSE, sep=",", sep2=",")

The first and third line read just fine and the second line throws a warning.

The issue happens when the line that throws the warning is wrapped up in a tryCatch block

tryCatch({
  fread("fails, rather\nbadly, too\nbad", header = FALSE, sep=",", sep2=",")
}, warning = function(w) {
  conditionMessage(w)
})

fread("will, work\njust, fine\nthank, you", header = FALSE, sep=",", sep2=",")

Calling the last fread throws a warning message, even though it should work just fine:

Warning message:
In fread("will, work\njust, fine\nthank, you", header = FALSE, sep = ",",  :
  Previous fread() session was not cleaned up properly. Cleaned up ok at the beginning of this fread() call.

sessionInfo:

R version 3.4.4 (2018-03-15)
Platform: x86_64-pc-linux-gnu (64-bit)
Running under: Ubuntu 16.04.4 LTS

Matrix products: default
BLAS: /usr/lib/libblas/libblas.so.3.6.0
LAPACK: /usr/lib/lapack/liblapack.so.3.6.0

locale:
 [1] LC_CTYPE=en_CA.UTF-8       LC_NUMERIC=C               LC_TIME=en_CA.UTF-8       
 [4] LC_COLLATE=en_CA.UTF-8     LC_MONETARY=en_CA.UTF-8    LC_MESSAGES=en_CA.UTF-8   
 [7] LC_PAPER=en_CA.UTF-8       LC_NAME=C                  LC_ADDRESS=C              
[10] LC_TELEPHONE=C             LC_MEASUREMENT=en_CA.UTF-8 LC_IDENTIFICATION=C       

attached base packages:
[1] stats     graphics  grDevices utils     datasets  methods   base     

other attached packages:
[1] data.table_1.11.2

loaded via a namespace (and not attached):
[1] compiler_3.4.4 tools_3.4.4
Dominant language
R
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