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Add max connections to prevent fds from hitting the limit #1217

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ad74430
#1188 fix: Add max connections to prevent fds from hitting the limit
aonq Aug 11, 2026
8d9745c
Use size_t with default 0 for max connections
aonq Aug 12, 2026
395667d
Update ssl_server initialization with max_connections
gittiver Aug 13, 2026
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14 changes: 11 additions & 3 deletions include/crow/app.h
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Original file line number Diff line number Diff line change
Expand Up @@ -464,6 +464,13 @@ namespace crow
return concurrency_;
}

/// \brief Set the maximum number of concurrent connections (default is unlimited with value 0)
self_t& max_connections(size_t size)
{
max_connections_ = size;
return *this;
}

/// \brief Set the server's log level
///
/// Possible values are:
Expand Down Expand Up @@ -639,7 +646,7 @@ namespace crow
}
tcp::endpoint endpoint(addr, port_);
router_.using_ssl = true;
ssl_server_ = std::move(std::unique_ptr<ssl_server_t>(new ssl_server_t(this, endpoint, server_name_, &middlewares_, concurrency_, timeout_, &ssl_context_, tcp_socket_options_)));
ssl_server_ = std::move(std::unique_ptr<ssl_server_t>(new ssl_server_t(this, endpoint, server_name_, &middlewares_, concurrency_, max_connections_, timeout_, &ssl_context_, tcp_socket_options_)));
ssl_server_->set_tick_function(tick_interval_, tick_function_);
ssl_server_->signal_clear();
for (auto snum : signals_)
Expand All @@ -655,7 +662,7 @@ namespace crow
if (use_unix_)
{
UnixSocketAcceptor::endpoint endpoint(bindaddr_);
unix_server_ = std::move(std::unique_ptr<unix_server_t>(new unix_server_t(this, endpoint, server_name_, &middlewares_, concurrency_, timeout_, nullptr)));
unix_server_ = std::move(std::unique_ptr<unix_server_t>(new unix_server_t(this, endpoint, server_name_, &middlewares_, concurrency_, max_connections_, timeout_, nullptr)));
unix_server_->set_tick_function(tick_interval_, tick_function_);
for (auto snum : signals_)
{
Expand All @@ -673,7 +680,7 @@ namespace crow
return;
}
TCPAcceptor::endpoint endpoint(addr, port_);
server_ = std::move(std::unique_ptr<server_t>(new server_t(this, endpoint, server_name_, &middlewares_, concurrency_, timeout_, nullptr, tcp_socket_options_)));
server_ = std::move(std::unique_ptr<server_t>(new server_t(this, endpoint, server_name_, &middlewares_, concurrency_, max_connections_, timeout_, nullptr, tcp_socket_options_)));
server_->set_tick_function(tick_interval_, tick_function_);
for (auto snum : signals_)
{
Expand Down Expand Up @@ -912,6 +919,7 @@ namespace crow
std::uint8_t timeout_{5};
uint16_t port_ = 80;
unsigned int concurrency_ = 2;
size_t max_connections_{};
std::atomic_bool is_bound_ = false;
uint64_t max_payload_{UINT64_MAX};
std::string server_name_ = std::string("Crow/") + VERSION;
Expand Down
12 changes: 10 additions & 2 deletions include/crow/http_server.h
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Original file line number Diff line number Diff line change
Expand Up @@ -22,6 +22,7 @@
#include <memory>
#include <thread>
#include <vector>
#include <optional>

#include "crow/version.h"
#include "crow/http_connection.h"
Expand Down Expand Up @@ -51,11 +52,13 @@ namespace crow // NOTE: Already documented in "crow/app.h"
std::string server_name = std::string("Crow/") + VERSION,
std::tuple<Middlewares...>* middlewares = nullptr,
unsigned int concurrency = 1,
size_t max_connections = 0,
uint8_t timeout = 5,
typename Adaptor::context* adaptor_ctx = nullptr,
detail::socket::tcp_socket_options tcp_socket_options = {}):
concurrency_(concurrency),
task_queue_length_pool_(concurrency_ - 1),
max_task_queue_length_(max_connections),
acceptor_(io_context_),
signals_(io_context_),
tick_timer_(io_context_),
Expand Down Expand Up @@ -318,8 +321,12 @@ namespace crow // NOTE: Already documented in "crow/app.h"

acceptor_.raw_acceptor().async_accept(
p->socket(),
[this, p, &ic](error_code ec) {
if (!ec)
[this, p, &ic, context_idx](error_code ec) {
if(max_task_queue_length_ > 0 && task_queue_length_pool_[context_idx] > max_task_queue_length_)
{
CROW_LOG_DEBUG << "Too many queued tasks for io context " << &ic << " {" << context_idx << "}, rejecting connection. Queue length: " << task_queue_length_pool_[context_idx];
}
else if (!ec)
{
detail::socket::apply_tcp_socket_options(p->socket(), tcp_socket_options_);
asio::post(ic,
Expand All @@ -343,6 +350,7 @@ namespace crow // NOTE: Already documented in "crow/app.h"
private:
unsigned int concurrency_{2};
std::vector<std::atomic<unsigned int>> task_queue_length_pool_;
size_t max_task_queue_length_{};
std::vector<std::unique_ptr<asio::io_context>> io_context_pool_;
asio::io_context io_context_;
std::vector<detail::task_timer*> task_timer_pool_;
Expand Down
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