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oxen-pyoxenmq
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Fix crash: don't create py::bytes inside request callback 

Requests were crashing and returning strange results because the GIL
wasn't held in the callback that was creating python `bytes` instances
in the callback.  Actually acquiring the gil, however, deadlocks.

So instead this keeps the future result as a C++ type and converts it to
python types when `get()` is called from Python.
This commit is contained in:
Jason Rhinelander 2020-08-19 18:24:23 -03:00
parent 08b2780df1
commit 9465aef0d6
1 changed files with 22 additions and 17 deletions
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39
pylokimq/lokimq.cpp
View File

@ -10,7 +10,7 @@
namespace lokimq
{
template <typename... Options>
std::future<std::vector<py::bytes>> LokiMQ_start_request(
std::future<std::vector<std::string>> LokiMQ_start_request(
LokiMQ& lmq,
ConnectionID conn,
std::string name,
@ -22,19 +22,13 @@ namespace lokimq
for (auto& b : byte_args)
args.push_back(b);
auto result = std::make_shared<std::promise<std::vector<py::bytes>>>();
auto result = std::make_shared<std::promise<std::vector<std::string>>>();
auto fut = result->get_future();
lmq.request(conn, std::move(name),
[result=std::move(result)](bool success, std::vector<std::string> value)
{
if (success)
{
std::vector<py::bytes> byte_values;
byte_values.reserve(value.size());
for (auto& v : value)
byte_values.emplace_back(std::move(v));
result->set_value(std::move(byte_values));
}
result->set_value(std::move(value));
else
{
std::string err;
@ -51,11 +45,13 @@ namespace lokimq
return fut;
}
template <typename F>
void bind_future(py::module& m, std::string class_name)
// Binds a stl future. `Conv` is a lambda that converts the future's .get() value into something
// Python-y (it can be the value directly, if the value is convertible to Python already).
template <typename F, typename Conv>
void bind_future(py::module& m, std::string class_name, Conv conv)
{
py::class_<F>(m, class_name.c_str())
.def("get", &F::get,
.def("get", [conv=std::move(conv)](F& f) { return conv(f.get()); },
"Gets the result (or raises an exception if the result set an exception); must only be called once")
.def("valid", [](F& f) { return f.valid(); },
"Returns true if the result is available")
@ -88,7 +84,13 @@ namespace lokimq
.value("deferred", std::future_status::deferred)
.value("ready", std::future_status::ready)
.value("timeout", std::future_status::timeout);
bind_future<std::future<std::vector<py::bytes>>>(mod, "ResultFuture");
bind_future<std::future<std::vector<std::string>>>(mod, "ResultFuture",
[](std::vector<std::string> bytes) {
py::list l;
for (const auto& v : bytes)
l.append(py::bytes(v));
return l;
});
py::class_<LokiMQ>(mod, "LokiMQ")
.def(py::init<>())
@ -176,11 +178,14 @@ namespace lokimq
ConnectionID conn,
std::string name,
std::vector<py::bytes> args,
std::optional<double> timeout) -> std::vector<py::bytes>
std::optional<double> timeout) -> py::list
{
return LokiMQ_start_request(self, conn, std::move(name), std::move(args),
py::list l;
for (auto& s : LokiMQ_start_request(self, conn, std::move(name), std::move(args),
lokimq::send_option::request_timeout{timeout ? std::chrono::milliseconds(long(*timeout * 1000)) : DEFAULT_REQUEST_TIMEOUT}
).get();
).get())
l.append(py::bytes(s));
return l;
},
"conn"_a, "name"_a, "args"_a = std::vector<py::bytes>{}, "timeout"_a = py::none{})
.def("request_future",
@ -188,7 +193,7 @@ namespace lokimq
ConnectionID conn,
std::string name,
std::vector<py::bytes> args,
std::optional<double> timeout) -> std::future<std::vector<py::bytes>>
std::optional<double> timeout) -> std::future<std::vector<std::string>>
{
return LokiMQ_start_request(self, conn, std::move(name), std::move(args),
lokimq::send_option::request_timeout{timeout ? std::chrono::milliseconds(long(*timeout * 1000)) : DEFAULT_REQUEST_TIMEOUT}