Fix busy loop when FDs are exhausted

cybozu/tcp.cpp

@@ -484,7 +484,8 @@ bool tcp_server_socket::on_readable() {
                 continue;
             if( errno == EMFILE || errno == ENFILE ) {
                 logger::error() << "accept: Too many open files.";
-                continue;
+                m_reactor->add_readable(*this);
+                break;
             }
             if( errno == EAGAIN || errno == EWOULDBLOCK )
                 break;

test/tcp.cpp

@@ -0,0 +1,82 @@
+#include <cybozu/reactor.hpp>
+#include <cybozu/signal.hpp>
+#include <cybozu/tcp.hpp>
+#include <cybozu/test.hpp>
+
+#include <arpa/inet.h>
+#include <sys/resource.h>
+#include <sys/socket.h>
+#include <sys/types.h>
+#include <signal.h>
+
+#include <atomic>
+#include <cstdlib>
+#include <memory>
+#include <thread>
+
+AUTOTEST(fd_exhausted) {
+    pid_t pid = ::fork();
+    if( pid == 0 ) { 
+        // server process
+
+        struct rlimit limit = {100, 100};
+        int e = ::setrlimit(RLIMIT_NOFILE, &limit);
+        if( e < 0 ) {
+            std::cout << "e = " << e << ", err = '" << strerror(errno) << "'\n";
+            cybozu_fail("setrlimit failed");
+            ::exit(1);
+        }
+
+        cybozu::reactor r;
+
+        auto sh = cybozu::signal_setup({SIGTERM});
+        sh->set_handler([](const struct signalfd_siginfo& si, cybozu::reactor& r) {
+            std::cerr << "got signal (signo=" << si.ssi_signo << ").";
+            r.quit();
+        });
+        r.add_resource(std::move(sh), cybozu::reactor::EVENT_IN);
+
+        struct dummy_socket : public cybozu::tcp_socket {
+            dummy_socket(int s): cybozu::tcp_socket(s) {}
+            virtual bool on_readable() override { return true; }
+        };
+        auto on_accept = [](int s, const cybozu::ip_address addr) {
+            return std::unique_ptr<cybozu::tcp_socket>(new dummy_socket(s));
+        };
+        r.add_resource(
+            std::unique_ptr<cybozu::resource>(
+                new cybozu::tcp_server_socket(nullptr, 11214, on_accept, false)
+            ),
+            cybozu::reactor::EVENT_IN);
+
+        r.run([](cybozu::reactor& r){});
+    } else {
+        // client process
+
+        ::sleep(1); // wait for server to start
+        for( int i = 0; i < 200; ++i ) {
+            int sockfd = ::socket(AF_INET, SOCK_STREAM, 0);
+            if( sockfd < 0 ) {
+                std::cout << "sockfd = " << sockfd << ", err = '" << strerror(errno) << "'\n";
+                cybozu_fail("failed to create client socket");
+                ::kill(pid, SIGKILL);
+                ::exit(1);
+            }
+            cybozu_assert( sockfd >= 0 );
+            struct sockaddr_in addr = {};
+            addr.sin_family = AF_INET;
+            ::inet_aton("127.0.0.1", &addr.sin_addr);
+            addr.sin_port = ::htons(11214);
+            int e = ::connect(sockfd, (struct sockaddr*)&addr, sizeof(addr));
+            if( e < 0 ) {
+                std::cout << "i = " << i << ", e = " << e << ", err = '" << strerror(errno) << "'\n";
+                cybozu_fail("failed to connect");
+                ::kill(pid, SIGKILL);
+                ::exit(1);
+            }
+        }
+        ::sleep(3);
+        // Cannot handle this signal if the reactor thread is in a busy loop.
+        ::kill(pid, SIGTERM);
+    }
+}