From 3d1ceac96af7eab5e7d7bbd5e1a1d6be7f1e67ee Mon Sep 17 00:00:00 2001
From: Eric Fischer <enf@pobox.com>
Date: Wed, 7 Dec 2016 11:16:34 -0800
Subject: [PATCH] Lock around setup of pipeline and filter process

---
 plugin.cpp | 20 ++++++++++++++++++++
 1 file changed, 20 insertions(+)

diff --git a/plugin.cpp b/plugin.cpp
index caa8494..d95011a 100644
--- a/plugin.cpp
+++ b/plugin.cpp
@@ -207,6 +207,8 @@ mvt_layer parse_layer(int fd, unsigned z, unsigned x, unsigned y, mvt_layer cons
 	return ret;
 }
 
+static pthread_mutex_t pipe_lock = PTHREAD_MUTEX_INITIALIZER;
+
 mvt_layer filter_layer(const char *filter, mvt_layer &layer, unsigned z, unsigned x, unsigned y) {
 	// This will create two pipes, a new thread, and a new process.
 	//
@@ -214,6 +216,11 @@ mvt_layer filter_layer(const char *filter, mvt_layer &layer, unsigned z, unsigne
 	// The new thread will write the GeoJSON to the pipe that leads to the filter.
 	// The original thread will read the GeoJSON from the filter and convert it back into vector tiles.
 
+	if (pthread_mutex_lock(&pipe_lock) != 0) {
+		perror("pthread_mutex_lock (pipe)");
+		exit(EXIT_FAILURE);
+	}
+
 	int pipe_orig[2], pipe_filtered[2];
 	if (pipe(pipe_orig) < 0) {
 		perror("pipe (original features)");
@@ -247,6 +254,14 @@ mvt_layer filter_layer(const char *filter, mvt_layer &layer, unsigned z, unsigne
 			perror("close input from filter");
 			exit(EXIT_FAILURE);
 		}
+		if (close(pipe_orig[0]) != 0) {
+			perror("close dup input of filter");
+			exit(EXIT_FAILURE);
+		}
+		if (close(pipe_filtered[1]) != 0) {
+			perror("close dup output of filter");
+			exit(EXIT_FAILURE);
+		}
 
 		// XXX close other fds?
 
@@ -267,6 +282,11 @@ mvt_layer filter_layer(const char *filter, mvt_layer &layer, unsigned z, unsigne
 			exit(EXIT_FAILURE);
 		}
 
+		if (pthread_mutex_unlock(&pipe_lock) != 0) {
+			perror("pthread_mutex_unlock (pipe_lock)");
+			exit(EXIT_FAILURE);
+		}
+
 		writer_arg wa;
 		wa.pipe_orig = pipe_orig;
 		wa.layer = &layer;