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Address #1125 - fix ev/select to only take and release locks once.

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By take and releasing locks twice per channel in the case where nothing
is reading, there was an opportunity for ev/select to hang in the
multithreaded case. Also silence valgrind/helgrind errors.
This commit is contained in:
Calvin Rose
2023-05-07 11:52:11 -05:00
parent cabbaded68
commit 2360164e4f
1 changed files with 56 additions and 29 deletions
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87
src/core/ev.c
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@@ -672,19 +672,6 @@ static void janet_chan_init(JanetChannel *chan, int32_t limit, int threaded) {
janet_os_mutex_init((JanetOSMutex *) &chan->lock);
}
static void janet_chan_deinit(JanetChannel *chan) {
janet_q_deinit(&chan->read_pending);
janet_q_deinit(&chan->write_pending);
if (janet_chan_is_threaded(chan)) {
Janet item;
while (!janet_q_pop(&chan->items, &item, sizeof(item))) {
janet_chan_unpack(chan, &item, 1);
}
}
janet_q_deinit(&chan->items);
janet_os_mutex_deinit((JanetOSMutex *) &chan->lock);
}
static void janet_chan_lock(JanetChannel *chan) {
if (!janet_chan_is_threaded(chan)) return;
janet_os_mutex_lock((JanetOSMutex *) &chan->lock);
@@ -695,6 +682,25 @@ static void janet_chan_unlock(JanetChannel *chan) {
janet_os_mutex_unlock((JanetOSMutex *) &chan->lock);
}
static void janet_chan_deinit(JanetChannel *chan) {
if (janet_chan_is_threaded(chan)) {
Janet item;
janet_chan_lock(chan);
janet_q_deinit(&chan->read_pending);
janet_q_deinit(&chan->write_pending);
while (!janet_q_pop(&chan->items, &item, sizeof(item))) {
janet_chan_unpack(chan, &item, 1);
}
janet_q_deinit(&chan->items);
janet_chan_unlock(chan);
} else {
janet_q_deinit(&chan->read_pending);
janet_q_deinit(&chan->write_pending);
janet_q_deinit(&chan->items);
}
janet_os_mutex_deinit((JanetOSMutex *) &chan->lock);
}
/*
* Janet Channel abstract type
*/
@@ -771,6 +777,7 @@ static void janet_thread_chan_cb(JanetEVGenericMessage msg) {
int mode = msg.tag;
JanetChannel *channel = (JanetChannel *) msg.argp;
Janet x = msg.argj;
janet_chan_lock(channel);
if (fiber->sched_id == sched_id) {
if (mode == JANET_CP_MODE_CHOICE_READ) {
janet_assert(!janet_chan_unpack(channel, &x, 0), "packing error");
@@ -791,7 +798,6 @@ static void janet_thread_chan_cb(JanetEVGenericMessage msg) {
int is_read = (mode == JANET_CP_MODE_CHOICE_READ) || (mode == JANET_CP_MODE_READ);
if (is_read) {
JanetChannelPending reader;
janet_chan_lock(channel);
if (!janet_q_pop(&channel->read_pending, &reader, sizeof(reader))) {
JanetVM *vm = reader.thread;
JanetEVGenericMessage msg;
@@ -802,10 +808,8 @@ static void janet_thread_chan_cb(JanetEVGenericMessage msg) {
msg.argj = x;
janet_ev_post_event(vm, janet_thread_chan_cb, msg);
}
janet_chan_unlock(channel);
} else {
JanetChannelPending writer;
janet_chan_lock(channel);
if (!janet_q_pop(&channel->write_pending, &writer, sizeof(writer))) {
JanetVM *vm = writer.thread;
JanetEVGenericMessage msg;
@@ -816,21 +820,21 @@ static void janet_thread_chan_cb(JanetEVGenericMessage msg) {
msg.argj = janet_wrap_nil();
janet_ev_post_event(vm, janet_thread_chan_cb, msg);
}
}
}
janet_chan_unlock(channel);
}
}
}
/* Push a value to a channel, and return 1 if channel should block, zero otherwise.
* If the push would block, will add to the write_pending queue in the channel.
* Handles both threaded and unthreaded channels. */
static int janet_channel_push(JanetChannel *channel, Janet x, int mode) {
static int janet_channel_push_with_lock(JanetChannel *channel, Janet x, int mode) {
JanetChannelPending reader;
int is_empty;
if (janet_chan_pack(channel, &x)) {
janet_chan_unlock(channel);
janet_panicf("failed to pack value for channel: %v", x);
}
janet_chan_lock(channel);
if (channel->closed) {
janet_chan_unlock(channel);
janet_panic("cannot write to closed channel");
@@ -891,12 +895,16 @@ static int janet_channel_push(JanetChannel *channel, Janet x, int mode) {
return 0;
}
static int janet_channel_push(JanetChannel *channel, Janet x, int mode) {
janet_chan_lock(channel);
return janet_channel_push_with_lock(channel, x, mode);
}
/* Pop from a channel - returns 1 if item was obtained, 0 otherwise. The item
* is returned by reference. If the pop would block, will add to the read_pending
* queue in the channel. */
static int janet_channel_pop(JanetChannel *channel, Janet *item, int is_choice) {
static int janet_channel_pop_with_lock(JanetChannel *channel, Janet *item, int is_choice) {
JanetChannelPending writer;
janet_chan_lock(channel);
if (channel->closed) {
janet_chan_unlock(channel);
*item = janet_wrap_nil();
@@ -941,6 +949,11 @@ static int janet_channel_pop(JanetChannel *channel, Janet *item, int is_choice)
return 1;
}
static int janet_channel_pop(JanetChannel *channel, Janet *item, int is_choice) {
janet_chan_lock(channel);
return janet_channel_pop_with_lock(channel, item, is_choice);
}
JanetChannel *janet_channel_unwrap(void *abstract) {
return abstract;
}
@@ -983,6 +996,20 @@ JANET_CORE_FN(cfun_channel_pop,
janet_await();
}
static void chan_unlock_args(const Janet *argv, int32_t n) {
for (int32_t i = 0; i < n; i++) {
int32_t len;
const Janet *data;
JanetChannel *chan;
if (janet_indexed_view(argv[i], &data, &len) && len == 2) {
chan = janet_getchannel(data, 0);
} else {
chan = janet_getchannel(argv, i);
}
janet_chan_unlock(chan);
}
}
JANET_CORE_FN(cfun_channel_choice,
"(ev/select & clauses)",
"Block until the first of several channel operations occur. Returns a tuple of the form [:give chan], [:take chan x], or [:close chan], where "
@@ -1002,29 +1029,29 @@ JANET_CORE_FN(cfun_channel_choice,
janet_chan_lock(chan);
if (chan->closed) {
janet_chan_unlock(chan);
chan_unlock_args(argv, i);
return make_close_result(chan);
}
if (janet_q_count(&chan->items) < chan->limit) {
janet_chan_unlock(chan);
janet_channel_push(chan, data[1], 1);
janet_channel_push_with_lock(chan, data[1], 1);
chan_unlock_args(argv, i);
return make_write_result(chan);
}
janet_chan_unlock(chan);
} else {
/* Read */
JanetChannel *chan = janet_getchannel(argv, i);
janet_chan_lock(chan);
if (chan->closed) {
janet_chan_unlock(chan);
chan_unlock_args(argv, i);
return make_close_result(chan);
}
if (chan->items.head != chan->items.tail) {
Janet item;
janet_chan_unlock(chan);
janet_channel_pop(chan, &item, 1);
janet_channel_pop_with_lock(chan, &item, 1);
chan_unlock_args(argv, i);
return make_read_result(chan, item);
}
janet_chan_unlock(chan);
}
}
@@ -1033,12 +1060,12 @@ JANET_CORE_FN(cfun_channel_choice,
if (janet_indexed_view(argv[i], &data, &len) && len == 2) {
/* Write */
JanetChannel *chan = janet_getchannel(data, 0);
janet_channel_push(chan, data[1], 1);
janet_channel_push_with_lock(chan, data[1], 1);
} else {
/* Read */
Janet item;
JanetChannel *chan = janet_getchannel(argv, i);
janet_channel_pop(chan, &item, 1);
janet_channel_pop_with_lock(chan, &item, 1);
}
}