Attempt to kill async worker process when new request comes in

See http://www.zsh.org/mla/users/2018/msg00432.html

src/async.zsh

@@ -3,21 +3,35 @@
 # Async                                                              #
 #--------------------------------------------------------------------#
 
+zmodload zsh/system
+
 _zsh_autosuggest_async_request() {
-	typeset -g _ZSH_AUTOSUGGEST_ASYNC_FD
+	typeset -g _ZSH_AUTOSUGGEST_ASYNC_FD _ZSH_AUTOSUGGEST_CHILD_PID
 
-	# Close the last fd to invalidate old suggestions
+	# If we've got a pending request, cancel it
 	if [[ -n "$_ZSH_AUTOSUGGEST_ASYNC_FD" ]] && { true <&$_ZSH_AUTOSUGGEST_ASYNC_FD } 2>/dev/null; then
+		# Close the file descriptor
 		exec {_ZSH_AUTOSUGGEST_ASYNC_FD}<&-
+
+		# Assume the child process created a new process group and send
+		# TERM to the group to attempt to kill all descendent processes
+		kill -TERM -$_ZSH_AUTOSUGGEST_CHILD_PID 2>/dev/null
 	fi
 
 	# Fork a process to fetch a suggestion and open a pipe to read from it
 	exec {_ZSH_AUTOSUGGEST_ASYNC_FD}< <(
+		# Tell parent process our pid
+		echo $sysparams[pid]
+
+		# Fetch and print the suggestion
 		local suggestion
 		_zsh_autosuggest_fetch_suggestion "$1"
 		echo -nE "$suggestion"
 	)
 
+	# Read the pid from the child process
+	read _ZSH_AUTOSUGGEST_CHILD_PID <&$_ZSH_AUTOSUGGEST_ASYNC_FD
+
 	# When the fd is readable, call the response handler
 	zle -F "$_ZSH_AUTOSUGGEST_ASYNC_FD" _zsh_autosuggest_async_response
 }

zsh-autosuggestions.zsh

@@ -581,21 +581,35 @@ _zsh_autosuggest_strategy_match_prev_cmd() {
 # Async                                                              #
 #--------------------------------------------------------------------#
 
+zmodload zsh/system
+
 _zsh_autosuggest_async_request() {
-	typeset -g _ZSH_AUTOSUGGEST_ASYNC_FD
+	typeset -g _ZSH_AUTOSUGGEST_ASYNC_FD _ZSH_AUTOSUGGEST_CHILD_PID
 
-	# Close the last fd to invalidate old suggestions
+	# If we've got a pending request, cancel it
 	if [[ -n "$_ZSH_AUTOSUGGEST_ASYNC_FD" ]] && { true <&$_ZSH_AUTOSUGGEST_ASYNC_FD } 2>/dev/null; then
+		# Close the file descriptor
 		exec {_ZSH_AUTOSUGGEST_ASYNC_FD}<&-
+
+		# Assume the child process created a new process group and send
+		# TERM to the group to attempt to kill all descendent processes
+		kill -TERM -$_ZSH_AUTOSUGGEST_CHILD_PID 2>/dev/null
 	fi
 
 	# Fork a process to fetch a suggestion and open a pipe to read from it
 	exec {_ZSH_AUTOSUGGEST_ASYNC_FD}< <(
+		# Tell parent process our pid
+		echo $sysparams[pid]
+
+		# Fetch and print the suggestion
 		local suggestion
 		_zsh_autosuggest_fetch_suggestion "$1"
 		echo -nE "$suggestion"
 	)
 
+	# Read the pid from the child process
+	read _ZSH_AUTOSUGGEST_CHILD_PID <&$_ZSH_AUTOSUGGEST_ASYNC_FD
+
 	# When the fd is readable, call the response handler
 	zle -F "$_ZSH_AUTOSUGGEST_ASYNC_FD" _zsh_autosuggest_async_response
 }