diff --git a/src/main.c b/src/main.c
index c6c905b4..54135f4b 100644
--- a/src/main.c
+++ b/src/main.c
@@ -320,6 +320,7 @@ typedef struct tf_run_args_t {
 	int count;
 	const char* args;
 	const char* zip;
+	bool one_proc;
 	bool help;
 } tf_run_args_t;
 
@@ -341,6 +342,7 @@ static int _tf_run_task(const tf_run_args_t* args, int index)
 	tf_task_set_http_port(task, args->http_port ? args->http_port + index : 0);
 	tf_task_set_https_port(task, args->https_port ? args->https_port + index : 0);
 	tf_task_set_args(task, args->args);
+	tf_task_set_one_proc(task, args->one_proc);
 	const char* db_path = args->db_path;
 	char db_path_buffer[256];
 	if (index)
@@ -385,6 +387,7 @@ static int _tf_command_run(const char* file, int argc, char* argv[])
 		{ "db-path", 'd', offsetof(tf_run_args_t, db_path), NULL, XOPT_TYPE_STRING, NULL, "Sqlite database path (default: db.sqlite)." },
 		{ "count", 'n', offsetof(tf_run_args_t, count), NULL, XOPT_TYPE_INT, NULL, "Number of instances to run." },
 		{ "args", 'a', offsetof(tf_run_args_t, args), NULL, XOPT_TYPE_STRING, NULL, "Arguments of the form key=value,foo=bar,verbose=true." },
+		{ "one-proc", 'o', offsetof(tf_run_args_t, one_proc), NULL, XOPT_TYPE_BOOL, NULL, "Run everything in one process (unsafely!)." },
 		{ "zip", 'z', offsetof(tf_run_args_t, zip), NULL, XOPT_TYPE_STRING, NULL, "Zip archive from which to load files." },
 		{ "help", 'h', offsetof(tf_run_args_t, help), NULL, XOPT_TYPE_BOOL, NULL, "Shows this help message." },
 		XOPT_NULLOPTION,
@@ -485,7 +488,7 @@ static int _tf_command_sandbox(const char* file, int argc, char* argv[])
 	prctl(PR_SET_PDEATHSIG, SIGHUP);
 #endif
 	tf_task_t* task = tf_task_create();
-	tf_task_configure_from_stdin(task);
+	tf_task_configure_from_fd(task, STDIN_FILENO);
 	shedPrivileges();
 	/* The caller will trigger tf_task_activate with a message. */
 	tf_task_run(task);
diff --git a/src/packetstream.c b/src/packetstream.c
index fbb417cb..0b1bca5a 100644
--- a/src/packetstream.c
+++ b/src/packetstream.c
@@ -1,5 +1,6 @@
 #include "packetstream.h"
 
+#include "log.h"
 #include "mem.h"
 
 #include "uv.h"
@@ -116,7 +117,11 @@ static void _packetstream_on_read(uv_stream_t* handle, ssize_t count, const uv_b
 void tf_packetstream_start(tf_packetstream_t* stream)
 {
 	stream->stream.data = stream;
-	uv_read_start((uv_stream_t*)&stream->stream, _packetstream_allocate, _packetstream_on_read);
+	int result = uv_read_start((uv_stream_t*)&stream->stream, _packetstream_allocate, _packetstream_on_read);
+	if (result)
+	{
+		tf_printf("uv_read_start: %s\n", uv_strerror(result));
+	}
 }
 
 static void _packetstream_on_write(uv_write_t* request, int status)
diff --git a/src/task.c b/src/task.c
index d51a8c02..ffee9df9 100644
--- a/src/task.c
+++ b/src/task.c
@@ -94,6 +94,7 @@ typedef struct _tf_task_t
 
 	bool _activated;
 	bool _trusted;
+	bool _one_proc;
 	bool _killed;
 	int32_t _exitCode;
 	char _scriptName[256];
@@ -1620,9 +1621,9 @@ tf_task_t* tf_task_create()
 	return task;
 }
 
-void tf_task_configure_from_stdin(tf_task_t* task)
+void tf_task_configure_from_fd(tf_task_t* task, int fd)
 {
-	task->_parent = tf_taskstub_create_parent(task, STDIN_FILENO);
+	task->_parent = tf_taskstub_create_parent(task, fd);
 }
 
 static void _tf_task_trace_to_parent(tf_trace_t* trace, const char* buffer, size_t size, void* user_data)
@@ -1754,6 +1755,16 @@ void tf_task_run(tf_task_t* task)
 	} while (_tf_task_run_jobs(task));
 }
 
+bool tf_task_get_one_proc(tf_task_t* task)
+{
+	return task->_one_proc;
+}
+
+void tf_task_set_one_proc(tf_task_t* task, bool one_proc)
+{
+	task->_one_proc = one_proc;
+}
+
 void tf_task_set_trusted(tf_task_t* task, bool trusted)
 {
 	task->_trusted = trusted;
diff --git a/src/task.h b/src/task.h
index 021fe097..bd99afde 100644
--- a/src/task.h
+++ b/src/task.h
@@ -35,7 +35,7 @@ typedef enum _tf_task_message_t {
 } tf_task_message_t;
 
 tf_task_t* tf_task_create();
-void tf_task_configure_from_stdin(tf_task_t* task);
+void tf_task_configure_from_fd(tf_task_t* task, int fd);
 void tf_task_set_ssb_port(tf_task_t* task, int port);
 void tf_task_set_http_port(tf_task_t* task, int port);
 void tf_task_set_https_port(tf_task_t* task, int port);
@@ -43,6 +43,8 @@ void tf_task_set_db_path(tf_task_t* task, const char* path);
 void tf_task_set_zip_path(tf_task_t* task, const char* path);
 const char* tf_task_get_zip_path(tf_task_t* task);
 void tf_task_set_args(tf_task_t* task, const char* args);
+bool tf_task_get_one_proc(tf_task_t* task);
+void tf_task_set_one_proc(tf_task_t* task, bool one_proc);
 void tf_task_activate(tf_task_t* task);
 void tf_task_run(tf_task_t* task);
 int tf_task_execute(tf_task_t* task, const char* file);
diff --git a/src/taskstub.js.c b/src/taskstub.js.c
index a7379b18..56d61b6b 100644
--- a/src/taskstub.js.c
+++ b/src/taskstub.js.c
@@ -63,6 +63,16 @@ static JSValue _taskstub_loadFile(JSContext* context, JSValueConst this_val, int
 static void _taskstub_on_process_exit(uv_process_t* process, int64_t status, int terminationSignal);
 static void _taskstub_finalizer(JSRuntime *runtime, JSValue value);
 
+static void _tf_taskstub_run_sandbox_thread(void* data)
+{
+	uv_file fd = (uv_file)(intptr_t)data;
+	tf_task_t* task = tf_task_create();
+	tf_task_configure_from_fd(task, fd);
+	/* The caller will trigger tf_task_activate with a message. */
+	tf_task_run(task);
+	tf_task_destroy(task);
+}
+
 static JSValue _taskstub_create(JSContext* context, JSValueConst this_val, int argc, JSValueConst* argv)
 {
 	tf_task_t* parent = tf_task_get(context);
@@ -125,41 +135,73 @@ static JSValue _taskstub_create(JSContext* context, JSValueConst this_val, int a
 	char arg1[] = "sandbox";
 	char* command_argv[] = { _executable, arg1, 0 };
 
-	uv_pipe_t* pipe = tf_packetstream_get_pipe(stub->_stream);
-	memset(pipe, 0, sizeof(*pipe));
-	if (uv_pipe_init(tf_task_get_loop(parent), pipe, 1) != 0)
-	{
-		tf_printf("uv_pipe_init failed\n");
-	}
-
-	uv_stdio_container_t io[3];
-	io[0].flags = UV_CREATE_PIPE | UV_READABLE_PIPE | UV_WRITABLE_PIPE;
-	io[0].data.stream = (uv_stream_t*)pipe;
-	io[1].flags = UV_INHERIT_FD;
-	io[1].data.fd = STDOUT_FILENO;
-	io[2].flags = UV_INHERIT_FD;
-	io[2].data.fd = STDERR_FILENO;
-
-	uv_process_options_t options = {0};
-	options.args = command_argv;
-	options.exit_cb = _taskstub_on_process_exit;
-	options.stdio = io;
-	options.stdio_count = sizeof(io) / sizeof(*io);
-	options.file = command_argv[0];
-
 	JSValue result = JS_NULL;
-	stub->_process.data = stub;
-	int spawn_result = uv_spawn(tf_task_get_loop(parent), &stub->_process, &options);
-	if (spawn_result == 0)
+	if (tf_task_get_one_proc(parent))
 	{
+		uv_os_sock_t fds[2];
+		int pipe_result = uv_socketpair(SOCK_STREAM, AF_UNIX, fds, 0, 0);
+		if (pipe_result)
+		{
+			tf_printf("uv_socketpair failed: %s\n", uv_strerror(pipe_result));
+		}
+
+		uv_pipe_t* pipe = tf_packetstream_get_pipe(stub->_stream);
+		memset(pipe, 0, sizeof(*pipe));
+		pipe_result = uv_pipe_init(tf_task_get_loop(parent), pipe, 1);
+		if (pipe_result != 0)
+		{
+			tf_printf("uv_pipe_init failed: %s\n", uv_strerror(pipe_result));
+		}
+		pipe_result = uv_pipe_open(pipe, fds[0]);
+		if (pipe_result != 0)
+		{
+			tf_printf("uv_pipe_open failed: %s\n", uv_strerror(pipe_result));
+		}
+
+		uv_thread_t* thread = tf_malloc(sizeof(uv_thread_t));
+		uv_thread_create(thread, _tf_taskstub_run_sandbox_thread, (void*)(intptr_t)fds[1]);
+
 		tf_packetstream_set_on_receive(stub->_stream, tf_task_on_receive_packet, stub);
 		tf_packetstream_start(stub->_stream);
 		result = taskObject;
 	}
 	else
 	{
-		tf_printf("uv_spawn failed: %s\n", uv_strerror(spawn_result));
-		JS_FreeValue(context, taskObject);
+		uv_pipe_t* pipe = tf_packetstream_get_pipe(stub->_stream);
+		memset(pipe, 0, sizeof(*pipe));
+		if (uv_pipe_init(tf_task_get_loop(parent), pipe, 1) != 0)
+		{
+			tf_printf("uv_pipe_init failed\n");
+		}
+
+		uv_stdio_container_t io[3];
+		io[0].flags = UV_CREATE_PIPE | UV_READABLE_PIPE | UV_WRITABLE_PIPE;
+		io[0].data.stream = (uv_stream_t*)pipe;
+		io[1].flags = UV_INHERIT_FD;
+		io[1].data.fd = STDOUT_FILENO;
+		io[2].flags = UV_INHERIT_FD;
+		io[2].data.fd = STDERR_FILENO;
+
+		uv_process_options_t options = {0};
+		options.args = command_argv;
+		options.exit_cb = _taskstub_on_process_exit;
+		options.stdio = io;
+		options.stdio_count = sizeof(io) / sizeof(*io);
+		options.file = command_argv[0];
+
+		stub->_process.data = stub;
+		int spawn_result = uv_spawn(tf_task_get_loop(parent), &stub->_process, &options);
+		if (spawn_result == 0)
+		{
+			tf_packetstream_set_on_receive(stub->_stream, tf_task_on_receive_packet, stub);
+			tf_packetstream_start(stub->_stream);
+			result = taskObject;
+		}
+		else
+		{
+			tf_printf("uv_spawn failed: %s\n", uv_strerror(spawn_result));
+			JS_FreeValue(context, taskObject);
+		}
 	}
 	return result;
 }
@@ -230,9 +272,10 @@ tf_taskstub_t* tf_taskstub_create_parent(tf_task_t* task, uv_file file)
 		tf_printf("uv_pipe_init failed\n");
 	}
 	tf_packetstream_set_on_receive(parentStub->_stream, tf_task_on_receive_packet, parentStub);
-	if (uv_pipe_open(tf_packetstream_get_pipe(parentStub->_stream), file) != 0)
+	int result = uv_pipe_open(tf_packetstream_get_pipe(parentStub->_stream), file);
+	if (result != 0)
 	{
-		tf_printf("uv_pipe_open failed\n");
+		tf_printf("uv_pipe_open failed: %s\n", uv_strerror(result));
 	}
 	tf_packetstream_start(parentStub->_stream);