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Make parallel merge even more robust #8

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Apr 29, 2024
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Make parallel merge even more robust #8

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25 changes: 14 additions & 11 deletions src/PDFmerger.jl
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Original file line number Diff line number Diff line change
Expand Up @@ -23,30 +23,33 @@ Merge all PDF files listed in `files` into a PDF named `destination`. Returns th
"""
function merge_pdfs(files::Vector{T}, destination::AbstractString="merged.pdf";
cleanup::Bool = false) where T <: AbstractString
# Get the process ID of the current Julia process and the ID of the current
# worker thread, such that separate process and workers create separate
# temporary files and do not mess up files of other workers.
process_id = getpid()
thread_id = myid()
identifier_stub = "_$(process_id)_$(thread_id)_"
if destination ∈ files
# rename existing file
Filesystem.mv(destination, destination * "_x_")
files[files .== destination] .= destination * "_x_"
Filesystem.mv(destination, destination * identifier_stub)
files[files .== destination] .= destination * identifier_stub
end

# Merge large number of files iteratively, because there
# is a (OS dependent) limit how many files 'pdfunit' can handel at once.
# is a (OS dependent) limit how many files 'pdfunit' can handle at once.
# See: https://gitlab.freedesktop.org/poppler/poppler/-/issues/334
filemax = 200

# Get the id of the current process/worker, such that separate workers
# create separate temporary files and do not mess up files of other workers.
procid = myid()
k = 1
for files_part in Base.Iterators.partition(files, filemax)
if k == 1
outfile_tmp2 = "_temp_destination_$(procid)_$k"
outfile_tmp2 = "_temp_destination_$(identifier_stub)_$k"

run(`$(pdfunite()) $files_part $outfile_tmp2`)

else
outfile_tmp1 = "_temp_destination_$(procid)_$(k-1)"
outfile_tmp2 = "_temp_destination_$(procid)_$k"
outfile_tmp1 = "_temp_destination_$(identifier_stub)_$(k-1)"
outfile_tmp2 = "_temp_destination_$(identifier_stub)_$k"

run(`$(pdfunite()) $outfile_tmp1 $files_part $outfile_tmp2`)

Expand All @@ -55,11 +58,11 @@ function merge_pdfs(files::Vector{T}, destination::AbstractString="merged.pdf";
end

# rename last file
Filesystem.mv("_temp_destination_$(procid)_$(k-1)", destination, force=true)
Filesystem.mv("_temp_destination_$(identifier_stub)_$(k-1)", destination, force=true)

# remove temp files
Filesystem.rm(destination * "_x_", force=true)
Filesystem.rm.("_temp_destination_$(procid)_$(i)" for i in 1:(k-2))
Filesystem.rm.("_temp_destination_$(identifier_stub)_$(i)" for i in 1:(k-2))
if cleanup
Filesystem.rm.(files, force=true)
end
Expand Down