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/**
* Copyright Amazon.com, Inc. or its affiliates. All Rights Reserved.
* SPDX-License-Identifier: Apache-2.0.
*/
#include <aws/common/private/thread_shared.h>
#include <aws/common/clock.h>
#include <aws/common/condition_variable.h>
#include <aws/common/linked_list.h>
#include <aws/common/mutex.h>
/*
* lock guarding the unjoined thread count and pending join list
*/
static struct aws_mutex s_managed_thread_lock = AWS_MUTEX_INIT;
static struct aws_condition_variable s_managed_thread_signal = AWS_CONDITION_VARIABLE_INIT;
static uint64_t s_default_managed_join_timeout_ns = 0;
/*
* The number of successfully launched managed threads (or event loop threads which participate by inc/dec) that
* have not been joined yet.
*/
static uint32_t s_unjoined_thread_count = 0;
/*
* A list of thread_wrapper structs for threads whose thread function has finished but join has not been called
* yet for the thread.
*
* This list is only ever at most length one.
*/
static struct aws_linked_list s_pending_join_managed_threads;
void aws_thread_increment_unjoined_count(void) {
aws_mutex_lock(&s_managed_thread_lock);
++s_unjoined_thread_count;
aws_mutex_unlock(&s_managed_thread_lock);
}
void aws_thread_decrement_unjoined_count(void) {
aws_mutex_lock(&s_managed_thread_lock);
--s_unjoined_thread_count;
aws_mutex_unlock(&s_managed_thread_lock);
aws_condition_variable_notify_one(&s_managed_thread_signal);
}
size_t aws_thread_get_managed_thread_count(void) {
size_t thread_count = 0;
aws_mutex_lock(&s_managed_thread_lock);
thread_count = s_unjoined_thread_count;
aws_mutex_unlock(&s_managed_thread_lock);
return thread_count;
}
static bool s_one_or_fewer_managed_threads_unjoined(void *context) {
(void)context;
return s_unjoined_thread_count <= 1;
}
void aws_thread_set_managed_join_timeout_ns(uint64_t timeout_in_ns) {
aws_mutex_lock(&s_managed_thread_lock);
s_default_managed_join_timeout_ns = timeout_in_ns;
aws_mutex_unlock(&s_managed_thread_lock);
}
int aws_thread_join_all_managed(void) {
struct aws_linked_list join_list;
aws_mutex_lock(&s_managed_thread_lock);
uint64_t timeout_in_ns = s_default_managed_join_timeout_ns;
aws_mutex_unlock(&s_managed_thread_lock);
uint64_t now_in_ns = 0;
uint64_t timeout_timestamp_ns = 0;
if (timeout_in_ns > 0) {
aws_sys_clock_get_ticks(&now_in_ns);
timeout_timestamp_ns = now_in_ns + timeout_in_ns;
}
bool successful = true;
bool done = false;
while (!done) {
aws_mutex_lock(&s_managed_thread_lock);
/*
* We lazily join old threads as newer ones finish their thread function. This means that when called from
* the main thread, there will always be one last thread (whichever completion serialized last) that is our
* responsibility to join (as long as at least one managed thread was created). So we wait for a count <= 1
* rather than what you'd normally expect (0).
*
* Absent a timeout, we only terminate if there are no threads left so it is possible to spin-wait a while
* if there is a single thread still running.
*/
if (timeout_timestamp_ns > 0) {
uint64_t wait_ns = 0;
/*
* now_in_ns is always refreshed right before this either outside the loop before the first iteration or
* after the previous wait when the overall timeout was checked.
*/
if (now_in_ns <= timeout_timestamp_ns) {
wait_ns = timeout_timestamp_ns - now_in_ns;
}
aws_condition_variable_wait_for_pred(
&s_managed_thread_signal,
&s_managed_thread_lock,
wait_ns,
s_one_or_fewer_managed_threads_unjoined,
NULL);
} else {
aws_condition_variable_wait_pred(
&s_managed_thread_signal, &s_managed_thread_lock, s_one_or_fewer_managed_threads_unjoined, NULL);
}
done = s_unjoined_thread_count == 0;
aws_sys_clock_get_ticks(&now_in_ns);
if (timeout_timestamp_ns != 0 && now_in_ns >= timeout_timestamp_ns) {
done = true;
successful = false;
}
aws_linked_list_init(&join_list);
aws_linked_list_swap_contents(&join_list, &s_pending_join_managed_threads);
aws_mutex_unlock(&s_managed_thread_lock);
/*
* Join against any finished threads. These threads are guaranteed to:
* (1) Not be the current thread
* (2) Have already ran to user thread_function completion
*
* The number of finished threads on any iteration is at most one.
*/
aws_thread_join_and_free_wrapper_list(&join_list);
}
return successful ? AWS_OP_SUCCESS : AWS_OP_ERR;
}
void aws_thread_pending_join_add(struct aws_linked_list_node *node) {
struct aws_linked_list join_list;
aws_linked_list_init(&join_list);
aws_mutex_lock(&s_managed_thread_lock);
/*
* Swap out the pending join threads before adding this, otherwise we'd join against ourselves which won't work
*/
aws_linked_list_swap_contents(&join_list, &s_pending_join_managed_threads);
aws_linked_list_push_back(&s_pending_join_managed_threads, node);
aws_mutex_unlock(&s_managed_thread_lock);
/*
* Join against any finished threads. This thread (it's only ever going to be at most one)
* is guaranteed to:
* (1) Not be the current thread
* (2) Has already ran to user thread_function completion
*/
aws_thread_join_and_free_wrapper_list(&join_list);
}
void aws_thread_initialize_thread_management(void) {
aws_linked_list_init(&s_pending_join_managed_threads);
}
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