I'm having trouble terminating my server in my multithreaded program (one server, multiple clients).
When the variable global_var, which counts the number of currently connected clients, gets set to 0, the server should terminate, but it doesn't.
What I think is happening is since accept() is blocking , the code never reaches the break condition in main loop.
It's breaking correctly out of thread_func but then it blocks inside the while loop, just before the accept() call and after printing "Exiting thread_func".
volatile int finished = 0; // Gets set to 1 by catching SIGINT/SIGSTOP
int global_var = 0; // When it gets to 0, server should terminate
int server_fd;
void * thread_func(void* arg)
{
do_some_pre_stuff();
while(1)
{
if(!global_var)
{
close(server_fd);
finished = 1;
break;
}
if(recv(...) > 0)
{
do_more_stuff()
}
else
{
disconnect_client();
global_var--;
break;
}
}
free_more_ressources();
return NULL;
}
int main()
{
do_initial_stuff();
init_socket();
listen();
while (!finished)
{
if( (fd = accept(server_fd,...)) == -1)
exit(-1);
global_var++;
/* Some intermediate code */
if(!global_var)
break;
// Thread for the newly connected player
if(pthread_create(&thread_id[...], NULL, thread_func, (void*)some_arg)
exit(-1);
}
free_resources();
puts("Exiting thread_func");
}
I tried the advice listed here without success (except the pipe answer, not trying to mess with pipes).
I'm new to socket programming but what I tried so far looked correct but none of the solutions worked (including semaphores, pthread_cancel,etc)
PS: synchronization has been implemented, just omitted here for readability
After installing zmq and czmq with brew, I tried to compile and play the Asynchronous-Majordomo-Pattern but it did not work as it requires czmq v3. As far as I understood, I tried to update it to the v4, using zactor because
zthread is deprecated in favor of zactor http://czmq.zeromq.org/czmq3-0:zthread
So right now the following code looks fine to me as updated async-majordomo pattern, but it does not work as expected, It does not create any thread when I run it via my terminal.
// Round-trip demonstrator
// While this example runs in a single process, that is just to make
// it easier to start and stop the example. The client task signals to
// main when it's ready.
#include "czmq.h"
#include <stdlib.h>
void dbg_write_in_file(char * txt, int nb_request) {
FILE * pFile;
pFile = fopen ("myfile.txt","a");
if (pFile!=NULL)
{
fputs (txt, pFile);
char str_nb_request[12];
sprintf(str_nb_request, "%d", nb_request);
fputs (str_nb_request, pFile);
fputs ("\n", pFile);
fclose (pFile);
}
}
static void
client_task (zsock_t *pipe, void *args)
{
zsock_t *client = zsock_new (ZMQ_DEALER);
zsock_connect (client, "tcp://localhost:5555");
printf ("Setting up test...\n");
zclock_sleep (100);
printf("child 1: parent: %i\n\n", getppid());
printf("child 1: my pid: %i\n\n", getpid());
int requests;
int64_t start;
printf ("Synchronous round-trip test...\n");
start = zclock_time ();
for (requests = 0; requests < 10000; requests++) {
zstr_send (client, "hello");
// stuck here /!\
char *reply = zstr_recv (client);
zstr_free (&reply);
// check if it does something
dbg_write_in_file("sync round-trip requests : ", requests);
// end check
}
printf (" %d calls/second\n",
(1000 * 10000) / (int) (zclock_time () - start));
printf ("Asynchronous round-trip test...\n");
start = zclock_time ();
for (requests = 0; requests < 100000; requests++) {
zstr_send (client, "hello");
// check if it does something
dbg_write_in_file("async round-trip send requests : ", requests);
// end check
}
for (requests = 0; requests < 100000; requests++) {
char *reply = zstr_recv (client);
zstr_free (&reply);
// check if it does something
dbg_write_in_file("async round-trip rec requests : ", requests);
// end check
}
printf (" %d calls/second\n",
(1000 * 100000) / (int) (zclock_time () - start));
zstr_send (pipe, "done");
}
// Here is the worker task. All it does is receive a message, and
// bounce it back the way it came:
static void
worker_task (zsock_t *pipe, void *args)
{
printf("child 2: parent: %i\n\n", getppid());
printf("child 2: my pid: %i\n\n", getpid());
zsock_t *worker = zsock_new (ZMQ_DEALER);
zsock_connect (worker, "tcp://localhost:5556");
while (true) {
zmsg_t *msg = zmsg_recv (worker);
zmsg_send (&msg, worker);
}
zsock_destroy (&worker);
}
// Here is the broker task. It uses the zmq_proxy function to switch
// messages between frontend and backend:
static void
broker_task (zsock_t *pipe, void *args)
{
printf("child 3: parent: %i\n\n", getppid());
printf("child 3: my pid: %i\n\n", getpid());
// Prepare our sockets
zsock_t *frontend = zsock_new (ZMQ_DEALER);
zsock_bind (frontend, "tcp://localhost:5555");
zsock_t *backend = zsock_new (ZMQ_DEALER);
zsock_bind (backend, "tcp://localhost:5556");
zmq_proxy (frontend, backend, NULL);
zsock_destroy (&frontend);
zsock_destroy (&backend);
}
// Finally, here's the main task, which starts the client, worker, and
// broker, and then runs until the client signals it to stop:
int main (void)
{
// Create threads
zactor_t *client = zactor_new (client_task, NULL);
assert (client);
zactor_t *worker = zactor_new (worker_task, NULL);
assert (worker);
zactor_t *broker = zactor_new (broker_task, NULL);
assert (broker);
// Wait for signal on client pipe
char *signal = zstr_recv (client);
zstr_free (&signal);
zactor_destroy (&client);
zactor_destroy (&worker);
zactor_destroy (&broker);
return 0;
}
When I run it, it looks like the program is stuck at the comment
// stuck here /!\
Then when I kill it as it does not finish, or print anything at all, I need to press five time Ctrl+C ( ^C ). Only then, it looks more verbose on the console, like it was indeed running. => Note that I delete all my printf() steps' outputs, as it was really messy to read.
When it runs, it does not write anything to the file, called by the dbg_write_in_file() function, only after sending five Ctrl+C ( ^C ).
Both client worker and broker task return the same getppid number ( my terminal ) and getpid as the program itself.
I use gcc trippingv4.c -o trippingv4 -L/usr/local/lib -lzmq -lczmq to compile.
When I try to kill it :
./trippingv4
Setting up test...
child 1: parent: 60967
child 1: my pid: 76853
Synchronous round-trip test...
^Cchild 2: parent: 60967
child 2: my pid: 76853
^Cchild 3: parent: 60967
child 3: my pid: 76853
^C^C^CE: 18-02-28 00:16:37 [76853]dangling 'PAIR' socket created at src/zsys.c:471
E: 18-02-28 00:16:37 [76853]dangling 'DEALER' socket created at trippingv4.c:29
E: 18-02-28 00:16:37 [76853]dangling 'PAIR' socket created at src/zsys.c:471
E: 18-02-28 00:16:37 [76853]dangling 'DEALER' socket created at trippingv4.c:89
Update
Thanks for the detailed answer #user3666197. In first part, the compiler does not compile the assert call so I just show the value instead and compare visually, they are the same.
int czmqMAJOR,
czmqMINOR,
czmqPATCH;
zsys_version ( &czmqMAJOR, &czmqMINOR, &czmqPATCH );
printf( "INF: detected CZMQ ( %d, %d, %d ) -version\n",
czmqMAJOR,
czmqMINOR,
czmqPATCH
);
printf( "INF: CZMQ_VERSION_MAJOR %d, CZMQ_VERSION_MINOR %d, CZMQ_VERSION_PATCH %d\n",
CZMQ_VERSION_MAJOR,
CZMQ_VERSION_MINOR,
CZMQ_VERSION_PATCH
);
Output :
INF: detected CZMQ ( 4, 1, 0 ) -version
INF: CZMQ_VERSION_MAJOR 4, CZMQ_VERSION_MINOR 1, CZMQ_VERSION_PATCH 0
The zsys_info call does compile but does not show anything on the terminal, even with a fflush(stdout) just in case so I just used printf :
INF: This system's Context() limit is 65535 ZeroMQ socketsINF: current state of the global Context()-instance has:
( 1 )-IO-threads ready
( 1 )-ZMQ_BLOCKY state
Then I changed the global context thread value with zsys_set_io_threads(2) and/or zmq_ctx_set (aGlobalCONTEXT, ZMQ_BLOCKY, false);, still blocked. It looks like zactor does not works with systems threads as zthread was... or does not gives a similar behavior. Given my experience in zeromq (also zero) probably I trying something that can't be achieved.
Update solved but unproper
My main error was to not have properly initiate zactor instance
An actor function MUST call zsock_signal (pipe) when initialized and MUST listen to pipe and exit on $TERM command.
And to not have blocked the zactor's proxy execution before it called zactor_destroy (&proxy);
I let the final code below but you still need to exit at the end with Ctrl+C because I did not figure it out how to manage $TERM signal properly. Also, zactor still appears to not use system theads. It's probably design like this but I don't know how it's work behind the wood.
// Round-trip demonstrator
// While this example runs in a single process, that is just to make
// it easier to start and stop the example. The client task signals to
// main when it's ready.
#include <czmq.h>
static void
client_task (zsock_t *pipe, void *args)
{
assert (streq ((char *) args, "Hello, Client"));
zsock_signal (pipe, 0);
zsock_t *client = zsock_new (ZMQ_DEALER);
zsock_connect (client, "tcp://127.0.0.1:5555");
printf ("Setting up test...\n");
zclock_sleep (100);
int requests;
int64_t start;
printf ("Synchronous round-trip test...\n");
start = zclock_time ();
for (requests = 0; requests < 10000; requests++) {
zstr_send (client, "hello");
zmsg_t *msgh = zmsg_recv (client);
zmsg_destroy (&msgh);
}
printf (" %d calls/second\n",
(1000 * 10000) / (int) (zclock_time () - start));
printf ("Asynchronous round-trip test...\n");
start = zclock_time ();
for (requests = 0; requests < 100000; requests++) {
zstr_send (client, "hello");
}
for (requests = 0; requests < 100000; requests++) {
char *reply = zstr_recv (client);
zstr_free (&reply);
}
printf (" %d calls/second\n",
(1000 * 100000) / (int) (zclock_time () - start));
zstr_send (pipe, "done");
printf("send 'done' to pipe\n");
}
// Here is the worker task. All it does is receive a message, and
// bounce it back the way it came:
static void
worker_task (zsock_t *pipe, void *args)
{
assert (streq ((char *) args, "Hello, Worker"));
zsock_signal (pipe, 0);
zsock_t *worker = zsock_new (ZMQ_DEALER);
zsock_connect (worker, "tcp://127.0.0.1:5556");
bool terminated = false;
while (!terminated) {
zmsg_t *msg = zmsg_recv (worker);
zmsg_send (&msg, worker);
// zstr_send (worker, "hello back"); // Give better perf I don't know why
}
zsock_destroy (&worker);
}
// Here is the broker task. It uses the zmq_proxy function to switch
// messages between frontend and backend:
static void
broker_task (zsock_t *pipe, void *args)
{
assert (streq ((char *) args, "Hello, Task"));
zsock_signal (pipe, 0);
// Prepare our proxy and its sockets
zactor_t *proxy = zactor_new (zproxy, NULL);
zstr_sendx (proxy, "FRONTEND", "DEALER", "tcp://127.0.0.1:5555", NULL);
zsock_wait (proxy);
zstr_sendx (proxy, "BACKEND", "DEALER", "tcp://127.0.0.1:5556", NULL);
zsock_wait (proxy);
bool terminated = false;
while (!terminated) {
zmsg_t *msg = zmsg_recv (pipe);
if (!msg)
break; // Interrupted
char *command = zmsg_popstr (msg);
if (streq (command, "$TERM")) {
terminated = true;
printf("broker received $TERM\n");
}
freen (command);
zmsg_destroy (&msg);
}
zactor_destroy (&proxy);
}
// Finally, here's the main task, which starts the client, worker, and
// broker, and then runs until the client signals it to stop:
int main (void)
{
// Create threads
zactor_t *client = zactor_new (client_task, "Hello, Client");
assert (client);
zactor_t *worker = zactor_new (worker_task, "Hello, Worker");
assert (worker);
zactor_t *broker = zactor_new (broker_task, "Hello, Task");
assert (broker);
char *signal = zstr_recv (client);
printf("signal %s\n", signal);
zstr_free (&signal);
zactor_destroy (&client);
printf("client done\n");
zactor_destroy (&worker);
printf("worker done\n");
zactor_destroy (&broker);
printf("broker done\n");
return 0;
}
Let's diagnose the as-is state, going step by step:
int czmqMAJOR,
czmqMINOR,
czmqPATCH;
zsys_version ( &czmqMAJOR, &czmqMINOR, &czmqPATCH );
printf( "INF: detected CZMQ( %d, %d, %d )-version",
czmqMAJOR,
czmqMINOR,
czmqPATCH
);
assert ( czmqMAJOR == CZMQ_VERSION_MAJOR & "Major: does not match\n" );
assert ( czmqMINOR == CZMQ_VERSION_MINOR & "Minor: does not match\n" );
assert ( czmqPATCH == CZMQ_VERSION_PATCH & "Patch: does not match\n" );
if this matches your expectations, you may hope the DLL-versions are both matching and found in proper locations.
Next:
may test the whole circus run in a non-blocking mode, to prove, there is no other blocker, but as briefly inspected, I have not found such option exposed in CZMQ-API, the native API allows one to flag a NOBLOCK option on { _send() | _recv() }-operations, which prevents them from remaining blocked ( which may be the case for DEALER socket instance in cases on _send()-s, when there are not yet any counterparty with a POSACK-ed .bind()/.connect() state ).
Here I did not find some tools to do this as fast as expected in native API. Maybe you will have more luck on going through this.
Test the presence of a global Context() instance, if it is ready:
add before a first socket instantiation, to be sure we are before any and all socket-generation and their respective _bind()/_connect() operation a following self-reporting row, using:
zsys_info ( "INF: This system's Context() limit is %zu ZeroMQ sockets",
zsys_socket_limit ()
);
One may also enforce the Context() instantiation manually:
so as to be sure the global Context() instance is up and running, before any higher abstracted instances ask if for implementing additional internalities ( sockets, counters, handlers, port-management, etc. )
// Initialize CZMQ zsys layer; this happens automatically when you create
// a socket or an actor; however this call lets you force initialization
// earlier, so e.g. logging is properly set-up before you start working.
// Not threadsafe, so call only from main thread. Safe to call multiple
// times. Returns global CZMQ context.
CZMQ_EXPORT void *
zsys_init (void);
// Optionally shut down the CZMQ zsys layer; this normally happens automatically
// when the process exits; however this call lets you force a shutdown
// earlier, avoiding any potential problems with atexit() ordering, especially
// with Windows dlls.
CZMQ_EXPORT void
zsys_shutdown (void);
and possibly better tune IO-performance, using this right at the initialisation state:
// Configure the number of I/O threads that ZeroMQ will use. A good
// rule of thumb is one thread per gigabit of traffic in or out. The
// default is 1, sufficient for most applications. If the environment
// variable ZSYS_IO_THREADS is defined, that provides the default.
// Note that this method is valid only before any socket is created.
CZMQ_EXPORT void
zsys_set_io_threads (size_t io_threads);
This manual instantiation gives one an additional benefit, from having the instance-handle void pointer, so that one can inspect it's current state and shape by zmq_ctx_get() tools:
void *aGlobalCONTEXT = zsys_init();
printf( "INF: current state of the global Context()-instance has:\n" );
printf( " ( %d )-IO-threads ready\n", zmq_ctx_get( aGlobalCONTEXT,
ZMQ_IO_THREADS
)
);
printf( " ( %d )-ZMQ_BLOCKY state\n", zmq_ctx_get( aGlobalCONTEXT,
ZMQ_BLOCKY
)
); // may generate -1 in case DLL is << 4.2+
...
If unhappy with signal-handling, one may design and use another one:
// Set interrupt handler; this saves the default handlers so that a
// zsys_handler_reset () can restore them. If you call this multiple times
// then the last handler will take affect. If handler_fn is NULL, disables
// default SIGINT/SIGTERM handling in CZMQ.
CZMQ_EXPORT void
zsys_handler_set (zsys_handler_fn *handler_fn);
where
// Callback for interrupt signal handler
typedef void (zsys_handler_fn) (int signal_value);
Here is a simple program using libevent on linux, it tracks the stdout fd, when it's writable, the callback will print some info to stdout.
Code
hello_libevent.c:
// libevent hello
#include <stdio.h>
#include <string.h>
#include <errno.h>
#include <unistd.h>
#include <event2/event.h>
#include <event2/thread.h>
void event_callback(evutil_socket_t fd, short events, void *arg) {
if(events | EV_WRITE) {
write(fd, "hello\n", 7);
}
sleep(1);
}
int libevent_test() {
int opr;
// enable pthread
if(evthread_use_pthreads() == -1) {
printf("error while evthread_use_pthreads(): %s\n", strerror(errno));
return -1;
}
// create event_base
struct event_base* eb;
if((eb = event_base_new()) == NULL) {
printf("error while event_base_new(): %s\n", strerror(errno));
return -1;
}
// create event
int fd_stdout = fileno(stdout);
struct event* event_stdout;
event_stdout = event_new(eb, fd_stdout, EV_WRITE, &event_callback, NULL);
// add event as pending
struct timeval timeout = {10, 0};
if(event_add(event_stdout, &timeout) == -1) {
printf("error while event_add(): %s\n", strerror(errno));
return -1;
}
// dispatch
if((opr = event_base_loop(eb, EVLOOP_NONBLOCK)) == -1) {
printf("error while event_base_dispatch(): %s\n", strerror(errno));
return -1;
} else if(opr == 1) {
printf("no more events\n");
} else {
printf("exit normally\n");
}
// free event
event_free(event_stdout);
return 0;
}
int main(int argc, char * argv[]) {
return libevent_test();
}
Compile:
gcc -Wall hello_libevent.c -levent -levent_pthreads
Execution result:
hello
no more events
Questions:
In the test, event only occur once, is that the expected behavior? Or it should loop to get more event until timeout?
How to make it get event continuously? Is it necessary to call event_base_loop within a loop, while it's already a loop?
I think the event flag EV_PERSIST mentioned in event.h File Reference might help.
Persistent event: won't get removed automatically when activated.
When a persistent event with a timeout becomes activated, its timeout is reset to 0.
Instead of
//...
event_stdout = event_new(eb, fd_stdout, EV_WRITE, &event_callback, NULL);
//...
you can pass this flag to event_new
//...
event_stdout = event_new(eb, fd_stdout, EV_WRITE|EV_PERSIST, &event_callback, NULL);
//...
and the other parts of code remain unchanged. At this time you create and add an event once and there's no need to call event_base_loop within a loop.
The compiled program just keeps printing lines of "hello" until it is terminated.
By the way, I noticed that changing
write(fd, "hello\n", 7);
into
write(fd, "hello\n", 6);
eliminates the leading character '\0' of each line.
From http://www.wangafu.net/~nickm/libevent-book/Ref3_eventloop.html it looks like you can call event_base_loop or event_base_dispatch from within a loop.
while (1) {
/* This schedules an exit ten seconds from now. */
event_base_loopexit(base, &ten_sec);``
event_base_dispatch(base);
puts("Tick");
}
The main purpose of events is to inform some busy thread about some event that happened elsewhere. So, this looks logical.
I'm trying to find out how to fix these memory leaks I'm getting while running this program with Valgrind. The leaks occur with the two allocations in nShell_client_main. But I'm not
sure how to properly free them.
I've tried freeing them at nShell_Connect, but it's causing libUV to abort the program. I've tried freeing them at the end of nShell_client_main, but then I get read/write errors when closing the loop. Does anyone know how I'm supposed to close these handles? I've read this, which got me started. But, it seams out-dated because uv_ip4_addr has a different prototype in the latest version.
(nShell_main is the "entry" point)
#include "nPort.h"
#include "nShell-main.h"
void nShell_Close(
uv_handle_t * term_handle
){
}
void nShell_Connect(uv_connect_t * term_handle, int status){
uv_close((uv_handle_t *) term_handle, 0);
}
nError * nShell_client_main(nShell * n_shell, uv_loop_t * n_shell_loop){
int uv_error = 0;
nError * n_error = 0;
uv_tcp_t * n_shell_socket = 0;
uv_connect_t * n_shell_connect = 0;
struct sockaddr_in dest_addr;
n_shell_socket = malloc(sizeof(uv_tcp_t));
if (!n_shell_socket){
// handle error
}
uv_error = uv_tcp_init(n_shell_loop, n_shell_socket);
if (uv_error){
// handle error
}
uv_error = uv_ip4_addr("127.0.0.1", NPORT, &dest_addr);
if (uv_error){
// handle error
}
n_shell_connect = malloc(sizeof(uv_connect_t));
if (!n_shell_connect){
// handle error
}
uv_error = uv_tcp_connect(n_shell_connect, n_shell_socket, (struct sockaddr *) &dest_addr, nShell_Connect);
if (uv_error){
// handle error
}
uv_error = uv_run(n_shell_loop, UV_RUN_DEFAULT);
if (uv_error){
// handle error
}
return 0;
}
nError * nShell_loop_main(nShell * n_shell){
int uv_error = 0;
nError * n_error = 0;
uv_loop_t * n_shell_loop = 0;
n_shell_loop = malloc(sizeof(uv_loop_t));
if (!n_shell_loop){
// handle error
}
uv_error = uv_loop_init(n_shell_loop);
if (uv_error){
// handle error
}
n_error = nShell_client_main(n_shell, n_shell_loop);
if (n_error){
// handle error
}
uv_loop_close(n_shell_loop);
free(n_shell_loop);
return 0;
}
The assertion is happening at the end of the switch statement in this excerpt of code (taken from Joyent's libUV page on Github):
void uv_close(uv_handle_t* handle, uv_close_cb close_cb) {
assert(!(handle->flags & (UV_CLOSING | UV_CLOSED)));
handle->flags |= UV_CLOSING;
handle->close_cb = close_cb;
switch (handle->type) {
case UV_NAMED_PIPE:
uv__pipe_close((uv_pipe_t*)handle);
break;
case UV_TTY:
uv__stream_close((uv_stream_t*)handle);
break;
case UV_TCP:
uv__tcp_close((uv_tcp_t*)handle);
break;
case UV_UDP:
uv__udp_close((uv_udp_t*)handle);
break;
case UV_PREPARE:
uv__prepare_close((uv_prepare_t*)handle);
break;
case UV_CHECK:
uv__check_close((uv_check_t*)handle);
break;
case UV_IDLE:
uv__idle_close((uv_idle_t*)handle);
break;
case UV_ASYNC:
uv__async_close((uv_async_t*)handle);
break;
case UV_TIMER:
uv__timer_close((uv_timer_t*)handle);
break;
case UV_PROCESS:
uv__process_close((uv_process_t*)handle);
break;
case UV_FS_EVENT:
uv__fs_event_close((uv_fs_event_t*)handle);
break;
case UV_POLL:
uv__poll_close((uv_poll_t*)handle);
break;
case UV_FS_POLL:
uv__fs_poll_close((uv_fs_poll_t*)handle);
break;
case UV_SIGNAL:
uv__signal_close((uv_signal_t*) handle);
/* Signal handles may not be closed immediately. The signal code will */
/* itself close uv__make_close_pending whenever appropriate. */
return;
default:
assert(0); // assertion is happening here
}
uv__make_close_pending(handle);
}
I could call uv__tcp_close manually, but it's not in the public headers (and probably not the right solution anyway).
libuv is not done with a handle until it's close callback is called. That is the exact moment when you can free the handle.
I see you call uv_loop_close, but you don't check for the return value. If there are still pending handles, it will return UV_EBUSY, so you should check for that.
If you want to close a loop and close all handles, you need to do the following:
Use uv_stop to stop the loop
Use uv_walk and call uv_close on all handles which are not closing
Run the loop again with uv_run so all close callbacks are called and you can free the memory in the callbacks
Call uv_loop_close, it should return 0 now
I finally figured out how to stop a loop and clean up all handles.
I created a bunch of handles and SIGINT signal handle:
uv_signal_t *sigint = new uv_signal_t;
uv_signal_init(uv_default_loop(), sigint);
uv_signal_start(sigint, on_sigint_received, SIGINT);
When SIGINT is received (Ctrl+C in console is pressed) the on_sigint_received callback is called.
The on_sigint_received looks like:
void on_sigint_received(uv_signal_t *handle, int signum)
{
int result = uv_loop_close(handle->loop);
if (result == UV_EBUSY)
{
uv_walk(handle->loop, on_uv_walk, NULL);
}
}
It triggers a call back function on_uv_walk:
void on_uv_walk(uv_handle_t* handle, void* arg)
{
uv_close(handle, on_uv_close);
}
It tries to close each opened libuv handle.
Note: that I do not call uv_stop before uv_walk, as mentioned saghul.
After on_sigint_received function is called libuv loop continuous the execution and on the next iteration calls on_uv_close for each opened handle. If you call the uv_stop function, then the on_uv_close callback will not be called.
void on_uv_close(uv_handle_t* handle)
{
if (handle != NULL)
{
delete handle;
}
}
After that libuv do not have opened handles and finishes the loop (exits from uv_run):
uv_run(uv_default_loop(), UV_RUN_DEFAULT);
int result = uv_loop_close(uv_default_loop());
if (result)
{
cerr << "failed to close libuv loop: " << uv_err_name(result) << endl;
}
else
{
cout << "libuv loop is closed successfully!\n";
}
I like the solution given by Konstantin Gindemit
I did run into a couple of problems however. His on_uv_close() function ends with a core dump. Also the uv_signal_t variable was causing valgrind to report a "definitely lost" memory leak.
I am using his code with fixes for these 2 situations.
void on_uv_walk(uv_handle_t* handle, void* arg) {
uv_close(handle, NULL);
}
void on_sigint_received(uv_signal_t *handle, int signum) {
int result = uv_loop_close(handle->loop);
if(result == UV_EBUSY) {
uv_walk(handle->loop, on_uv_walk, NULL);
}
}
int main(int argc, char *argv[]) {
uv_signal_t *sigint = new uv_signal_t;
uv_signal_init(uv_default_loop(), sigint);
uv_signal_start(sigint, on_sigint_received, SIGINT);
uv_loop_t* main_loop = uv_default_loop();
...
uv_run(main_loop, UV_RUN_DEFAULT));
uv_loop_close(uv_default_loop());
delete sigint;
return 0;
}
I have a worker thread processing a queue of work items.
//producer
void push_into_queue(char *item) {
pthread_mutex_lock (&queueMutex);
if(workQueue.full) { // full }
else{
add_item_into_queue(item);
pthread_cond_signal (&queueSignalPush);
}
pthread_mutex_unlock(&queueMutex);
}
// consumer1
void* worker(void* arg) {
while(true) {
pthread_mutex_lock(&queueMutex);
while(workQueue.empty)
pthread_cond_wait(&queueSignalPush, &queueMutex);
item = workQueue.front; // pop from queue
add_item_into_list(item);
// do I need another signal here for thread2?
pthread_cond_signal(&queueSignalPop);
pthread_mutex_unlock(&queueMutex);
}
return NULL;
}
pthread_create (&thread1, NULL, (void *) &worker, NULL);
Now I would like to have thread2 consume the data inserted in add_item_into_list() but only if items have been added to the list. Note that the list is permanent and can't be emptied nor freed for the entire duration of the program.
So my question is: do I need another pthread_cond_signal?, if yes, where would this signal go? and how my other worker would look like (canonical form)?
I see 2 possible ways of solving the problem:
a. Introduce another condition variable (e.g. signalList) for the list, so that consumer2 thread would wait for events on it. In this case consumer1 have to signal twice: once on queueSignalPop and once on signalList:
// consumer1
void* worker(void* arg) {
while(true) {
// ...
pthread_cond_signal(&queueSignalPop);
pthread_cond_signal(&signalList);
pthread_mutex_unlock(&queueMutex);
}
return NULL;
}
b. Use existing condition queueSignalPop variable inside consumer2 to wait for events, and use broadcast instead of signal inside consumer1. Broadcast means all the waiting threads on condition variable will wake up:
// consumer1
void* worker(void* arg) {
while(true) {
// ...
pthread_cond_broadcast(&queueSignalPop);
pthread_mutex_unlock(&queueMutex);
}
return NULL;
}
// consumer2
void* worker2(void* arg) {
while(true) {
while(list.empty)
pthread_cond_wait(&queueSignalPop, &queueMutex);
// ...
}
return NULL;
}
I would propose to go for the first approach, since it better distinguish the purpose of each condition variable.