diff --git a/codearchiver-bot b/codearchiver-bot
index 05db19a..dd2d61d 100755
--- a/codearchiver-bot
+++ b/codearchiver-bot
@@ -113,52 +113,50 @@ function respond {
 	done |
 
 	# The actual work loop
-	while :; do
-		# Process in batches for efficiency of parallel IA processing after uploads
-		declare -a batch=()
-		while read -r -t 1 line; do
-			batch+=("${line}")
-		done
+	while IFS= read -r line; do
+		singlejobid="${line%% *}"
+		line="${line#* }"
+		nick="${line%% *}"
+		url="${line#* }"
 
-		if [[ ${#batch[@]} -eq 0 ]]; then
+		# Handle marker for end of list job: tell the user it's done and move on.
+		if [[ "${url}" == 'end' ]]; then
+			# No status code reflection here because the start of the list job might not even have been in this batch.
+			respond "${nick}" "Job ${singlejobid} finished."
 			continue
 		fi
 
-		newfiles=()
-
-		for ((i=0; i<${#batch[@]}; ++i)); do
-			line="${batch[${i}]}"
-			singlejobid="${line%% *}"
-			line="${line#* }"
-			nick="${line%% *}"
-			url="${line#* }"
-
-			# Handle marker for end of list job: tell the user it's done and move on.
-			if [[ "${url}" == 'end' ]]; then
-				# No status code reflection here because the start of the list job might not even have been in this batch.
-				respond "${nick}" "Job ${singlejobid} finished."
-				continue
-			fi
-
-			# Find nonexistent filename for log file (*not* concurrency-safe!)
-			logbasename="$(date +%Y%m%dT%H%M%SZ)_${singlejobid}"
-			if [[ -e "${logbasename}_codearchiver.log" || -e "${logbasename}_codearchiver.log.zst" ]]; then
-				for ((j=0; ; ++j)); do
-					if [[ ! -e "${logbasename}_coll${j}_codearchiver.log" || -e "${logbasename}_coll${j}_codearchiver.log.zst" ]]; then
-						break
-					fi
-				done
-				logbasename="${logbasename}_coll${j}"
-			fi
-			logname="${logbasename}_codearchiver.log"
-			artefactsname="${logbasename}_codearchiver_artefacts.txt"
+		# Find nonexistent filename for log file with lock
+		# mkdir is pretty much always atomic, creating files might not be depending on the underlying file system (e.g. networked ones like NFS).
+		while ! mkdir '.loglock' 2> >(log_loop 'mkdir loglock (work) err: '); do
+			sleep 1
+		done
+		trap 'rmdir ".loglock"' EXIT  # Unlock if something below fails
+		logbasename="$(date +%Y%m%dT%H%M%SZ)_${singlejobid}"
+		if [[ -e "${logbasename}_codearchiver.log" || -e "${logbasename}_codearchiver.log.zst" ]]; then
+			for ((j=0; ; ++j)); do
+				if [[ ! -e "${logbasename}_coll${j}_codearchiver.log" || -e "${logbasename}_coll${j}_codearchiver.log.zst" ]]; then
+					break
+				fi
+			done
+			logbasename="${logbasename}_coll${j}"
+		fi
+		logname="${logbasename}_codearchiver.log"
+		artefactsname="${logbasename}_codearchiver_artefacts.txt"
+		# Create the log file already in case spawning the tee process for it below is too slow
+		touch "${logname}"
+		trap - EXIT  # Reset trap
+		rmdir '.loglock'  # Unlock
 
-			# Run codearchiver, duplicating WARNINGs and higher in the bot output
-			log "Running ${url} (${singlejobid}), logging into ${logname}"
+		# Run codearchiver in a background shell, duplicating WARNINGs and higher in the bot output
+		# Produces lines of filenames to upload on stdout
+		log "Running ${url} (${singlejobid}), logging into ${logname}"
+		(
 			timeout --signal=INT "${timeout}" \
 				codearchiver --verbose --write-artefacts-fd-3 "${url}" \
-				2> >(tee "${logname}" | grep -Fv -e '  INFO  ' | log_loop "From codearchiver ${singlejobid}: ") \
-				3> >(tee "${artefactsname}" | log_loop "New artefacts from codearchiver ${singlejobid}: ")
+				> >(log_loop "codearchiver ${singlejobid} out: ") \
+				2> >(tee "${logname}" | grep -Fv -e '  INFO  ' | log_loop "codearchiver ${singlejobid} err: ") \
+				3> >(tee "${artefactsname}" | log_loop "Artefact from codearchiver ${singlejobid}: ")
 			status="$?"
 			log "codearchiver ${url} finished with status code ${status}"
 			#TODO Integrate this into the pipe from codearchiver above to avoid rereading the entire log file
@@ -181,11 +179,11 @@ function respond {
 				mv --verbose -- "${artefacts[@]}" "${artefactsname}" ./failed/ 2> >(log_loop 'mv err: ') | log_loop 'mv out: '
 			else
 				for file in "${artefacts[@]}"; do
-					newfiles+=("${file}")
+					printf '%s\n' "${file}"
 				done
-				newfiles+=("${artefactsname}")
+				printf '%s\n' "${artefactsname}"
 			fi
-			newfiles+=("${logname}")
+			printf '%s\n' "${logname}"
 
 			# For individual jobs, tell the user about warnings and success/failure
 			if [[ "${singlejobid}" != *_* ]]; then
@@ -199,11 +197,23 @@ function respond {
 					respond "${nick}" "Job ${singlejobid} produced ${badcount} warnings or errors."
 				fi
 			fi
+		) &
+		wait
+	done |
+
+	# Upload
+	while :; do
+		# Process in batches for efficiency of parallel IA upload processing
+		declare -a filenames=()
+		while read -r -t 1 filename; do
+			filenames+=("${filename}")
 		done
+		if [[ ${#filenames[@]} -eq 0 ]]; then
+			continue
+		fi
 
 		# Record SHA-256 hashes for new files
-		log "SHA-256 hashes:"
-		sha256sum "${newfiles[@]}" > >(log_loop 'sha256sum: ')
+		sha256sum "${filenames[@]}" > >(log_loop 'sha256sum: ')
 
 		# Upload
 		date="$(date '+%Y-%m-%d')"
@@ -215,7 +225,7 @@ function respond {
 			collection='test_collection'
 		fi
 		uploadsfine=y
-		for f in "${newfiles[@]}"; do
+		for f in "${filenames[@]}"; do
 			ia-upload-stream --no-derive "${identifier}" "${f}" \
 				"collection:${collection}" \
 				'mediatype:software' \
@@ -231,24 +241,34 @@ function respond {
 			fi
 		done
 
-		if [[ "${uploadsfine}" ]]; then
-			# Wait until all tasks for the item are done
-			while :; do
-				tasks="$(python3 -c 'import json, sys; o = json.load(sys.stdin); print(sum(o["value"]["summary"].values()))' < <({ curl --silent --verbose --fail --max-time 10 --header "Authorization: LOW ${IA_S3_ACCESS}:${IA_S3_SECRET}" "https://archive.org/services/tasks.php?identifier=${identifier}&summary=1&history=0" 2> >(log_loop 'curl IA tasks err: '); } | tee >(log_loop 'curl IA tasks out: ')))"
-				if [[ "${tasks}" == '0' ]]; then
-					break
-				fi
-				sleep 60
-			done
-
-			# Replace non-metadata files with a symlink to .uploaded dummy file
-			touch '.uploaded'
-			for f in "${newfiles[@]}"; do
-				if [[ "${f}" != *_codearchiver_metadata.txt ]]; then
-					log "Replacing ${f} with symlink to .uploaded"
-					{ rm --verbose -- "${f}" && ln --symbolic --verbose '.uploaded' "${f}"; } |& log_loop 'rm/ln: '
-				fi
-			done
+		if [[ -z "${uploadsfine}" ]]; then
+			continue
 		fi
+
+		# Wait until all tasks for the item are done
+		while :; do
+			tasks="$(python3 -c 'import json, sys; o = json.load(sys.stdin); print(sum(o["value"]["summary"].values()))' < <({ curl --silent --verbose --fail --max-time 10 --header "Authorization: LOW ${IA_S3_ACCESS}:${IA_S3_SECRET}" "https://archive.org/services/tasks.php?identifier=${identifier}&summary=1&history=0" 2> >(log_loop 'curl IA tasks err: '); } | tee >(log_loop 'curl IA tasks out: ')))"
+			if [[ "${tasks}" == '0' ]]; then
+				break
+			fi
+			sleep 60
+		done
+
+		# Replace non-metadata files with a symlink to .uploaded dummy file
+		# No locking with codearchiver processes is necessary because those will only read metadata (which is left alone) or write files.
+		# However, a lock with the log filename finding is required.
+		while ! mkdir '.loglock' 2> >(log_loop 'mkdir loglock (upload) err: '); do
+			sleep 1.1  # Slightly longer than above to minimise repeated collisions
+		done
+		trap 'rmdir ".loglock"' EXIT
+		touch '.uploaded'
+		for f in "${filenames[@]}"; do
+			if [[ "${f}" != *_codearchiver_metadata.txt ]]; then
+				log "Replacing ${f} with symlink to .uploaded"
+				{ rm --verbose -- "${f}" && ln --symbolic --verbose '.uploaded' "${f}"; } |& log_loop 'rm/ln: '
+			fi
+		done
+		trap - EXIT
+		rmdir '.loglock'
 	done
 }