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thpool.c
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thpool.c
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/* thpool.c: implementation of thpool.h */
#include "thpool.h"
#include <stdlib.h>
#include <signal.h>
#include <pthread.h> // requires -lpthread at link time
#include <unistd.h>
#include <errno.h>
#include <setjmp.h>
#include <assert.h>
/* ========================================================================
* struct Threadpool definition
* ======================================================================== */
typedef struct {
void (*func) (void* arg);
void* arg;
} ThreadpoolJob;
#define THREADPOOL_MAX_JOB_NUM 65536
typedef struct {
uint64_t id; // id of the worker; also index of its Thread struct
// in the internal array of the Threadpool it belongs to
pthread_t pthread;
Threadpool* restrict pool;
jmp_buf* restrict envp; // for proper cleanup on hard shutdown
} Thread;
struct Threadpool {
pthread_mutex_t lock;
pthread_cond_t worker_event;
pthread_cond_t queue_not_full;
pthread_cond_t th_all_idle;
pthread_cond_t th_init_done;
volatile int64_t shutdown;
volatile int64_t pause;
volatile int64_t jobqueue_len;
volatile int64_t jobqueue_head;
volatile int64_t jobqueue_tail;
ThreadpoolJob jobqueue[THREADPOOL_MAX_JOB_NUM]; // circular queue
int64_t init_capacity;
volatile int64_t thnum_active;
volatile int64_t thnum_alive;
Thread threads[];
};
// Global handle to the threadpool; Necessary because it's not possible to pass
// extra arguments to signal handlers. Using a global handle restricts the
// number of Threadpool to only one. I.e. a process must not create multiple
// Threadpools.
static Threadpool* g_tp_handle;
/* ========================================================================
* function implementations
* ======================================================================== */
/* usage: given a threadpool, check if its jobqueue is full. This function
* may only be called when holding the mutex of the pool.
* params:
* tp: ptr to Threadpool
* return: true if full; false otherwise */
static inline bool
thpool_jobqueue_full(const Threadpool* tp) {
return tp->jobqueue_len == THREADPOOL_MAX_JOB_NUM;
}
/* usage: given a threadpool, check if its jobqueue is empty. This function
* may only be called when holding the mutex of the pool.
* params:
* tp: ptr to Threadpool
* return: true if empty; false otherwise */
static inline bool
thpool_jobqueue_empty(const Threadpool* tp) {
return tp->jobqueue_len == 0;
}
/* usage: given a threadpool and a job, store the job into its job queue. This
* function may only be called when holding the mutex of the pool, and
* when the job queue is not full.
* params:
* 1) tp: ptr to Threadpool
* 2) job: ptr to struct ThreadpoolJob
* return: void */
static inline void
thpool_job_enqueue(Threadpool* restrict tp, const ThreadpoolJob* restrict job) {
assert(!thpool_jobqueue_full(tp));
if(tp->jobqueue_head == -1)
tp->jobqueue_head = 0;
tp->jobqueue_tail = (tp->jobqueue_tail + 1) % THREADPOOL_MAX_JOB_NUM;
tp->jobqueue[tp->jobqueue_tail] = *job;
tp->jobqueue_len++;
assert(0 <= tp->jobqueue_len);
assert(tp->jobqueue_len <= THREADPOOL_MAX_JOB_NUM);
}
/* usage: given a threadpool, pop a job from its job queue. This function
* may only be called when holding the mutex of the pool, and when the job
* queue is not empty.
* params:
* 1) tp: ptr to Threadpool
* 2) job: ptr to struct ThreadpoolJob; container for the job
* return: void */
static inline void
thpool_job_dequeue(Threadpool* restrict tp, ThreadpoolJob* restrict job) {
assert(tp->jobqueue_head != -1);
assert(!thpool_jobqueue_empty(tp));
*job = tp->jobqueue[tp->jobqueue_head];
if(tp->jobqueue_head == tp->jobqueue_tail)
tp->jobqueue_head = tp->jobqueue_tail = -1;
else
tp->jobqueue_head = (tp->jobqueue_head + 1) % THREADPOOL_MAX_JOB_NUM;
tp->jobqueue_len--;
assert(0 <= tp->jobqueue_len);
assert(tp->jobqueue_len < THREADPOOL_MAX_JOB_NUM);
}
/* usage: given a threadpool, return the number of workers that are still alive
* in the pool.
* params:
* 1) tp: ptr to Threadpool
* return: the number of workers on success; negative value on error */
int64_t
thpool_alive_worker_num(Threadpool* tp) {
if(!tp)
return Threadpool_null;
if(pthread_mutex_lock(&tp->lock))
return Threadpool_lock_fail;
volatile int64_t num = tp->thnum_alive;
assert(tp->thnum_alive >= tp->thnum_active);
if(pthread_mutex_unlock(&tp->lock))
return Threadpool_lock_fail;
return num;
}
/* usage: signal handler for thpool_worker; on SIGUSR1, pause the thread */
static inline void
thpool_worker_sa_handler_pause(int sig_id) {
(void) sig_id; // get rid of 'unused param' warning from compiler
Threadpool* tp = g_tp_handle;
if(!tp)
return;
// NOTE: cannot use a condition variable because only async-signal-safe
// functions are allowed in a signal handler.
while(tp->pause)
sleep(1);
}
/* usage: signal handler for thpool_worker; on SIGUSR2, terminate the thread */
static inline void
thpool_worker_sa_handler_terminate(int sig_id) {
(void) sig_id; // get rid of 'unused param' warning from compiler
Threadpool* tp = g_tp_handle;
if(!tp)
return;
// find the Thread data structure for this thread; just do
// a linear search because there're not so many threads.
pthread_t own_pid = pthread_self();
int64_t idx = -1;
for(int64_t i = 0; i < tp->init_capacity; ++i) {
if(tp->threads[i].pthread == own_pid) {
idx = i;
break;
}
}
assert(idx != -1);
longjmp(*(tp->threads[idx].envp), 36); // NOTE: 2nd param can be anything
}
/* usage: internal worker that dequeue jobs from the jobqueue and execute them.
* params:
* 1) t: ptr to Thread storing info for the worker
* return : void*, as per requirement of pthread */
static inline void*
thpool_worker(Thread* t) {
// register signal handlers
struct sigaction sig_info;
sigset_t block_mask;
sigemptyset(&block_mask);
sigaddset(&block_mask, SIGUSR2); // block signals for hard shutdown
sig_info.sa_mask = block_mask;
sig_info.sa_flags = 0;
sig_info.sa_handler = thpool_worker_sa_handler_pause;
if(sigaction(SIGUSR1, &sig_info, NULL)) {
return NULL;
}
sigemptyset(&block_mask);
sigaddset(&block_mask, SIGUSR1); // block signals for pause
sig_info.sa_mask = block_mask;
sig_info.sa_handler = thpool_worker_sa_handler_terminate;
if(sigaction(SIGUSR2, &sig_info, NULL)) {
return NULL;
}
Threadpool* const tp = t->pool;
if(pthread_mutex_lock(&tp->lock))
return NULL;
tp->thnum_alive++;
if(pthread_cond_signal(&tp->th_init_done)) {
tp->thnum_alive--;
pthread_mutex_unlock(&tp->lock);
return NULL;
}
assert(tp->thnum_alive >= 0);
if(pthread_mutex_unlock(&tp->lock)) {
tp->thnum_alive--;
return NULL;
}
// set up a recovery point for hard shutdown
jmp_buf env;
t->envp = &env;
int jmp_v = setjmp(env);
if(jmp_v) { // return from signal handler for SIGUSR2
// try to release the lock in case this thread currently owns it. If the
// thread is not the owner, the function should only return EPERM since the
// lock is robust and should not trigger a deadlock. Note that this
// cannot be performed inside the signal handler because
// pthread_mutex_unlock() is not async-signal-safe.
int rv = pthread_mutex_unlock(&tp->lock);
if(rv && rv != EPERM)
return NULL;
}
while(!jmp_v) {
if(pthread_mutex_lock(&tp->lock)) {
// cannot update thnum_alive before returning
return NULL;
}
while(thpool_jobqueue_empty(tp) && !tp->shutdown) {
if(pthread_cond_wait(&tp->worker_event, &tp->lock)) {
tp->thnum_alive--;
pthread_mutex_unlock(&tp->lock);
return NULL;
}
}
if(tp->shutdown) {
if(pthread_mutex_unlock(&tp->lock)) {
tp->thnum_alive--;
return NULL;
} else
break;
}
if(thpool_jobqueue_full(tp) &&
pthread_cond_signal(&tp->queue_not_full)) {
tp->thnum_alive--;
pthread_mutex_unlock(&tp->lock);
return NULL;
}
ThreadpoolJob job; // small enough to use stack memory
thpool_job_dequeue(tp, &job);
assert(!thpool_jobqueue_full(tp));
tp->thnum_active++;
assert(tp->thnum_alive >= tp->thnum_active && tp->thnum_active >= 0);
if(pthread_mutex_unlock(&tp->lock)) {
tp->thnum_active--;
tp->thnum_alive--;
return NULL;
}
job.func(job.arg);
if(pthread_mutex_lock(&tp->lock)) {
// cannot update thnum_alive before returning
return NULL;
}
if(0 == --(tp->thnum_active) && thpool_jobqueue_empty(tp) &&
pthread_cond_signal(&tp->th_all_idle)) {
tp->thnum_alive--;
pthread_mutex_unlock(&tp->lock);
return NULL;
}
assert(tp->thnum_alive >= tp->thnum_active && tp->thnum_active >= 0);
if(pthread_mutex_unlock(&tp->lock)) {
tp->thnum_alive--;
return NULL;
}
}
if(pthread_mutex_lock(&tp->lock))
return NULL;
tp->thnum_alive--;
assert(tp->thnum_alive >= 0);
// terminating anyway; no need to check return value
pthread_mutex_unlock(&tp->lock);
return NULL;
}
/* usage: subroutine of thpool_create(). Wait until threads created earlier are
* initialized, then perform a soft shutdown.
* params:
* 1) tp: ptr to Threadpool
* 2) n: the number of threads that has been created
* return: 0 on success; non-zero on error */
static inline int
thpool_worker_init_abort(Threadpool* tp, int64_t n) {
if(!n)
return 0;
if(pthread_mutex_lock(&tp->lock))
return Threadpool_lock_fail;
while(tp->thnum_alive < n) {
if(pthread_cond_wait(&tp->th_init_done, &tp->lock)) {
pthread_mutex_unlock(&tp->lock);
return Threadpool_cond_fail;
}
}
tp->shutdown = 1; // do a soft shutdown
if(pthread_mutex_unlock(&tp->lock))
return Threadpool_lock_fail;
// wake up all workers
if(pthread_cond_broadcast(&tp->worker_event))
return Threadpool_cond_fail;
for(int64_t i = 0; i < n; ++i) {
if(pthread_join(tp->threads[i].pthread, NULL))
return Threadpool_join_fail;
}
assert(tp->thnum_alive == 0);
assert(tp->thnum_active == 0);
return 0;
}
/* usage: create and initialize a threadpool; A process may only create one
* Threadpool at a time.
* params:
* 1) n: number of worker threads to create in the threadpool
* return: a ptr to Threadpool on success; NULL on error */
Threadpool*
thpool_create(int64_t n) {
if(g_tp_handle) // there can only be 1 Threadpool at a time
return NULL;
if(n <= 0)
return NULL;
if(n > THREADPOOL_MAX_JOB_NUM)
n = THREADPOOL_MAX_JOB_NUM; // higher thread count makes no sense
Threadpool* tp = malloc(sizeof(Threadpool) + sizeof(Thread) * n);
if(!tp)
return NULL;
pthread_mutexattr_t lock_attr; // use a robust lock
if(pthread_mutexattr_init(&lock_attr)) {
free(tp);
return NULL;
}
if(pthread_mutexattr_setrobust(&lock_attr, PTHREAD_MUTEX_ROBUST) ||
pthread_mutex_init(&tp->lock, &lock_attr)) {
pthread_mutexattr_destroy(&lock_attr);
free(tp);
return NULL;
}
if(pthread_mutexattr_destroy(&lock_attr)) {
pthread_mutex_destroy(&tp->lock);
free(tp);
return NULL;
}
if(pthread_cond_init(&tp->worker_event, NULL)) {
pthread_mutex_destroy(&tp->lock);
free(tp);
return NULL;
}
if(pthread_cond_init(&tp->queue_not_full, NULL)) {
pthread_cond_destroy(&tp->worker_event);
pthread_mutex_destroy(&tp->lock);
free(tp);
return NULL;
}
if(pthread_cond_init(&tp->th_all_idle, NULL)) {
pthread_cond_destroy(&tp->queue_not_full);
pthread_cond_destroy(&tp->worker_event);
pthread_mutex_destroy(&tp->lock);
free(tp);
return NULL;
}
if(pthread_cond_init(&tp->th_init_done, NULL)) {
pthread_cond_destroy(&tp->th_all_idle);
pthread_cond_destroy(&tp->queue_not_full);
pthread_cond_destroy(&tp->worker_event);
pthread_mutex_destroy(&tp->lock);
free(tp);
return NULL;
}
tp->shutdown = 0;
tp->pause = 0;
tp->jobqueue_len = 0;
tp->jobqueue_head = -1;
tp->jobqueue_tail = -1;
tp->init_capacity = n;
tp->thnum_active = 0;
tp->thnum_alive = 0;
// init threads
for(int64_t i = 0; i < n; ++i) {
tp->threads[i].id = i;
tp->threads[i].pool = tp;
if(pthread_create(&tp->threads[i].pthread, NULL,
(void* (*) (void*)) thpool_worker,
(void*) (tp->threads + i))) {
if(thpool_worker_init_abort(tp, i)) {
// NOTE: cannot release lock and condition vars in this case
return NULL;
}
pthread_cond_destroy(&tp->th_init_done);
pthread_cond_destroy(&tp->th_all_idle);
pthread_cond_destroy(&tp->queue_not_full);
pthread_cond_destroy(&tp->worker_event);
pthread_mutex_destroy(&tp->lock);
free(tp);
return NULL;
}
}
if(pthread_mutex_lock(&tp->lock)) {
// fail to acquire the lock already, calling thpool_worker_init_abort()
// makes no sense
// NOTE: cannot destory the condition vars in this case
return NULL;
}
while(tp->thnum_alive != n) {
if(pthread_cond_wait(&tp->th_init_done, &tp->lock)) {
// th_init_done malfunctions already, calling
// thpool_worker_init_abort() makes no sense
pthread_mutex_unlock(&tp->lock);
return NULL;
}
}
if(pthread_mutex_unlock(&tp->lock)) {
// fail to unlock the lock already; cannot call
// thpool_worker_init_abort()
return NULL;
}
// update the global handle
g_tp_handle = tp;
return tp;
}
/* usage: given a threadpool, add a job to execute into the pool. This function
* blocks the calling thread if the job queue in the pool is full.
* params:
* 1) tp: ptr to Threadpool
* 2) func: function ptr to execute whose signature is void (*) (void*)
* 3) arg: ptr to void, which is the argument for the function ptr
* return: 0 if success; non-zero on error */
int
thpool_add_job(Threadpool* restrict tp, void (*f) (void*), void* restrict arg) {
if(!tp)
return Threadpool_null;
if(pthread_mutex_lock(&tp->lock))
return Threadpool_lock_fail;
while(thpool_jobqueue_full(tp) && !tp->shutdown) {
if(pthread_cond_wait(&tp->queue_not_full, &tp->lock)) {
pthread_mutex_unlock(&tp->lock);
return Threadpool_cond_fail;
}
}
if(tp->shutdown) {
if(pthread_mutex_unlock(&tp->lock))
return Threadpool_lock_fail;
return Threadpool_shutdown;
}
ThreadpoolJob job = { .func = f, .arg = arg };
thpool_job_enqueue(tp, &job);
if(pthread_mutex_unlock(&tp->lock))
return Threadpool_lock_fail;
if(pthread_cond_signal(&tp->worker_event))
return Threadpool_cond_fail;
return 0;
}
/* usage: given a threadpool, clear all queued jobs.
* params:
* 1) tp: ptr to Threadpool
* return: 0 on success; non-zero value on error */
int
thpool_clear_jobs(Threadpool* tp) {
if(!tp)
return Threadpool_null;
if(pthread_mutex_lock(&tp->lock))
return Threadpool_lock_fail;
tp->jobqueue_head = -1;
tp->jobqueue_tail = -1;
tp->jobqueue_len = 0;
if(pthread_mutex_unlock(&tp->lock))
return Threadpool_lock_fail;
if(pthread_cond_broadcast(&tp->queue_not_full)) {
return Threadpool_cond_fail;
}
return 0;
}
/* usage: Given a threadpool; check if all queued jobs are done
* and all workers are idle
* params:
* 1) tp: ptr to Threadpool
* return: 1 if idle; 0 if not; negative value on error */
int
thpool_idle(Threadpool* tp) {
if(!tp)
return Threadpool_null;
if(pthread_mutex_lock(&tp->lock))
return Threadpool_lock_fail;
int rv = thpool_jobqueue_empty(tp) && (tp->thnum_active == 0);
if(pthread_mutex_unlock(&tp->lock))
return Threadpool_lock_fail;
return rv;
}
/* usage: Given a threadpool, block the calling thread until all
* queued jobs are finished
* params:
* 1) tp: ptr to Threadpool
* return: 0 on success; non-zero value on error */
int
thpool_wait_jobs(Threadpool* tp) {
if(!tp)
return Threadpool_null;
if(pthread_mutex_lock(&tp->lock))
return Threadpool_lock_fail;
while(!tp->shutdown && (!thpool_jobqueue_empty(tp) || tp->thnum_active)) {
if(pthread_cond_wait(&tp->th_all_idle, &tp->lock)) {
pthread_mutex_unlock(&tp->lock);
return Threadpool_cond_fail;
}
}
int rv = tp->shutdown ? Threadpool_shutdown : 0;
if(pthread_mutex_unlock(&tp->lock))
return Threadpool_lock_fail;
return rv;
}
/* usage: Given a threadpool, pause all its workers. This function does nothing
* if the threadpool has been shut down.
* params:
* 1) tp: ptr to threadpool
* return: 0 on success; non-zero value on error */
int
thpool_pause(Threadpool* tp) {
if(!tp)
return Threadpool_null;
if(pthread_mutex_lock(&tp->lock))
return Threadpool_lock_fail;
volatile int64_t shutdown = tp->shutdown;
if(pthread_mutex_unlock(&tp->lock))
return Threadpool_lock_fail;
if(shutdown)
return Threadpool_shutdown;
if(pthread_mutex_lock(&tp->lock))
return Threadpool_lock_fail;
tp->pause = 1; // NOTE: the workers do not modify it
if(pthread_mutex_unlock(&tp->lock))
return Threadpool_lock_fail;
for(int64_t i = 0; i < tp->init_capacity; ++i) {
int rv = pthread_kill(tp->threads[i].pthread, SIGUSR1);
if(rv == ESRCH) // the thread has joined
continue;
else if(rv)
return Threadpool_kill_fail;
}
return 0;
}
/* usage: Given a threadpool, resume all its workers. This function does nothing
* if the threadpool has been shut down.
* params:
* 1) tp: ptr to threadpool
* return: 0 on success; non-zero value on error */
int
thpool_resume(Threadpool* tp) {
if(!tp)
return Threadpool_null;
if(pthread_mutex_lock(&tp->lock))
return Threadpool_lock_fail;
volatile int64_t shutdown = tp->shutdown;
if(pthread_mutex_unlock(&tp->lock))
return Threadpool_lock_fail;
if(shutdown)
return Threadpool_shutdown;
if(pthread_mutex_lock(&tp->lock))
return Threadpool_lock_fail;
tp->pause = 0; // NOTE: the workers do not modify it
if(pthread_mutex_unlock(&tp->lock))
return Threadpool_lock_fail;
return 0;
}
/* usage: Given a threadpool, kill all its workers. Note that there might be
* unexecuted jobs left in the pool and the states of resouces (e.g. mutex
* and condition variable) accessed in the job can be undefined.
*
* If this function encounter errors when killing the workers, it returns a
* non-zero value and may leave some workers alive.
*
* The threadpool becomes inoperable after this function returns and the
* only valid function call left is thpool_destroy().
*
* If the workers are paused and not yet resumed, this function will
* resume the workers before killing them.
* params:
* 1) tp: ptr to threadpool
* return : 0 on success; non-zero value on error */
int
thpool_hard_shutdown(Threadpool* tp) {
if(!tp)
return Threadpool_null;
// wake up paused workers (if any) first, otherwise SIGUSR2 will be blocked
int rv = thpool_resume(tp);
if(rv)
return rv;
// first try a soft shutdown
if(pthread_mutex_lock(&tp->lock))
return Threadpool_lock_fail;
if(tp->shutdown) { // already shutdown
pthread_mutex_unlock(&tp->lock);
return Threadpool_shutdown;
}
tp->shutdown = 1;
if(pthread_mutex_unlock(&tp->lock))
return Threadpool_lock_fail;
// wake up all workers and threads blocking on the pool
if(pthread_cond_broadcast(&tp->worker_event) ||
pthread_cond_broadcast(&tp->queue_not_full) ||
pthread_cond_broadcast(&tp->th_all_idle))
return Threadpool_cond_fail;
// TODO: do we need this?
if(usleep(5000)) // wait for (some) threads to terminate properly
return Threadpool_sleep_fail;
// check if there's still worker alive
volatile int tnum = (int) thpool_alive_worker_num(tp);
if(tnum < 0)
return tnum;
// then perform the hard shutdown if necessary
if(tnum > 0) {
for(int64_t i = 0; i < tp->init_capacity; ++i) {
int rv = pthread_kill(tp->threads[i].pthread, SIGUSR2);
if(rv == ESRCH) // the thread has joined
continue;
else if(rv)
return Threadpool_kill_fail;
}
}
for(int64_t i = 0; i < tp->init_capacity; ++i) {
if(pthread_join(tp->threads[i].pthread, NULL)) {
return Threadpool_join_fail;
}
}
tp->thnum_active = 0;
tp->thnum_alive = 0;
return 0;
}
/* usage: Given a threadpool, wait until all the workers finish their current
* jobs, and then terminate workers in the threadpool. The threadpool
* becomes inoperable after this function returns and the only valid
* function call left is thpool_destroy().
*
* If the workers are paused and not yet resumed, this function will
* resume the workers before shutting them down.
* params:
* 1) tp: ptr to threadpool
* return: 0 on success; non-zero value on error */
static inline int
thpool_soft_shutdown(Threadpool* tp) {
if(!tp)
return Threadpool_null;
// wake up paused workers (if any) first
int rv = thpool_resume(tp);
if(rv)
return rv;
if(pthread_mutex_lock(&tp->lock))
return Threadpool_lock_fail;
if(tp->shutdown) { // already shutdown
pthread_mutex_unlock(&tp->lock);
return Threadpool_shutdown;
}
tp->shutdown = 1;
if(pthread_mutex_unlock(&tp->lock))
return Threadpool_lock_fail;
// wake up all workers and threads blocking on the pool
if(pthread_cond_broadcast(&tp->worker_event) ||
pthread_cond_broadcast(&tp->queue_not_full) ||
pthread_cond_broadcast(&tp->th_all_idle))
return Threadpool_cond_fail;
for(int64_t i = 0; i < tp->init_capacity; ++i) {
if(pthread_join(tp->threads[i].pthread, NULL))
return Threadpool_join_fail;
}
assert(tp->thnum_alive == 0);
assert(tp->thnum_active == 0);
return 0;
}
/* usage: Given a threadpool, terminate all its workers and release its
* resources. The terminination can be soft or hard:
*
* soft: wait until all workers finish their current jobs
* hard: terminate the workers immediately without waiting
*
* Hard terminination might leave system resources accessed or allocated
* in user supplied jobs in an undefined state, and should be used as a
* last resort.
*
* This function will simply release resources of the threadpool if a
* shutdown has been performed.
* params:
* 1) tp: ptr to Threadpool
* 2) type: false for hard terminination, true for soft terminination
* return: 0 on success; non-zero value on error */
int
thpool_destroy(Threadpool* tp, bool type) {
if(!tp)
return Threadpool_null;
if(pthread_mutex_lock(&tp->lock))
return Threadpool_lock_fail;
volatile int64_t shutdown = tp->shutdown;
if(pthread_mutex_unlock(&tp->lock))
return Threadpool_lock_fail;
if(!shutdown) {
int rv = type ? thpool_soft_shutdown(tp) : thpool_hard_shutdown(tp);
if(rv)
return rv;
}
assert(tp->shutdown == 1);
assert(tp->thnum_alive == 0);
assert(tp->thnum_active == 0);
// NOTE: destroying locked mutex and condition var is undefined behavior
if(pthread_mutex_destroy(&tp->lock) ||
pthread_cond_destroy(&tp->worker_event) ||
pthread_cond_destroy(&tp->queue_not_full) ||
pthread_cond_destroy(&tp->th_all_idle) ||
pthread_cond_destroy(&tp->th_init_done))
return Threadpool_free_fail;
g_tp_handle = NULL; // reset the global handle
free(tp);
return 0;
}