2021-07-30 15:39:02

by Riccardo Mancini

[permalink] [raw]
Subject: [RFC PATCH v2 03/10] perf workqueue: add threadpool start and stop functions

This patch adds the start and stop functions, alongside the thread
function.
Each thread will run until a stop signal is received.
Furthermore, start and stop are added to the test.

Thread management is based on the prototype from Alexey:
https://lore.kernel.org/lkml/[email protected]/

Suggested-by: Alexey Bayduraev <[email protected]>
Signed-off-by: Riccardo Mancini <[email protected]>
---
tools/perf/tests/workqueue.c | 13 +
tools/perf/util/workqueue/threadpool.c | 328 ++++++++++++++++++++++++-
tools/perf/util/workqueue/threadpool.h | 9 +
3 files changed, 347 insertions(+), 3 deletions(-)

diff --git a/tools/perf/tests/workqueue.c b/tools/perf/tests/workqueue.c
index fb0e86390d466677..767e4fb60be4b190 100644
--- a/tools/perf/tests/workqueue.c
+++ b/tools/perf/tests/workqueue.c
@@ -11,16 +11,29 @@ struct threadpool_test_args_t {

static int __threadpool__prepare(struct threadpool **pool, int pool_size)
{
+ int ret;
+
*pool = threadpool__new(pool_size);
TEST_ASSERT_VAL("threadpool creation failure", !IS_ERR(*pool));
TEST_ASSERT_VAL("threadpool size is wrong",
threadpool__size(*pool) == pool_size);

+ ret = threadpool__start(*pool);
+ TEST_ASSERT_VAL("threadpool start failure", ret == 0);
+ TEST_ASSERT_VAL("threadpool is not ready", threadpool__is_ready(*pool));
+
return TEST_OK;
}

static int __threadpool__teardown(struct threadpool *pool)
{
+ int ret;
+
+ ret = threadpool__stop(pool);
+ TEST_ASSERT_VAL("threadpool stop failure", ret == 0);
+ TEST_ASSERT_VAL("stopped threadpool is ready",
+ !threadpool__is_ready(pool));
+
threadpool__delete(pool);

return TEST_OK;
diff --git a/tools/perf/util/workqueue/threadpool.c b/tools/perf/util/workqueue/threadpool.c
index 0004ce606d5fa73d..850ef7e110566536 100644
--- a/tools/perf/util/workqueue/threadpool.c
+++ b/tools/perf/util/workqueue/threadpool.c
@@ -4,20 +4,38 @@
#include <unistd.h>
#include <errno.h>
#include <string.h>
+#include <pthread.h>
+#include <signal.h>
+#include <syscall.h>
#include "debug.h"
#include <asm/bug.h>
#include <linux/zalloc.h>
#include <linux/string.h>
#include <linux/err.h>
#include <linux/kernel.h>
+#include <internal/lib.h>
#include "threadpool.h"

+#ifndef HAVE_GETTID
+static inline pid_t gettid(void)
+{
+ return (pid_t)syscall(__NR_gettid);
+}
+#endif
+
enum threadpool_status {
THREADPOOL_STATUS__STOPPED, /* no threads */
+ THREADPOOL_STATUS__READY, /* threads are ready but idle */
THREADPOOL_STATUS__ERROR, /* errors */
THREADPOOL_STATUS__MAX
};

+static const char * const threadpool_status_tags[] = {
+ "stopped",
+ "ready",
+ "error"
+};
+
struct threadpool {
int nr_threads; /* number of threads in the pool */
struct threadpool_entry *threads; /* array of threads in the pool */
@@ -35,6 +53,29 @@ struct threadpool_entry {
} pipes;
};

+enum threadpool_msg {
+ THREADPOOL_MSG__UNDEFINED = 0,
+ THREADPOOL_MSG__ACK, /* from th: create and exit ack */
+ THREADPOOL_MSG__WAKE, /* to th: wake up */
+ THREADPOOL_MSG__STOP, /* to th: exit */
+ THREADPOOL_MSG__MAX
+};
+
+static const char * const threadpool_msg_tags[] = {
+ "undefined",
+ "ack",
+ "wake",
+ "stop"
+};
+
+static const char * const threadpool_errno_str[] = {
+ "Error calling sigprocmask",
+ "Error receiving message from thread",
+ "Error sending message to thread",
+ "Thread sent unexpected message",
+ "This operation is not allowed in this state"
+};
+
/**
* threadpool_entry__init_pipes - initialize all pipes of @thread
*/
@@ -93,6 +134,130 @@ static void threadpool_entry__close_pipes(struct threadpool_entry *thread)
}
}

+/**
+ * threadpool__wait_thread - receive ack from thread
+ *
+ * NB: call only from main thread!
+ */
+static int threadpool__wait_thread(struct threadpool_entry *thread)
+{
+ int res;
+ enum threadpool_msg msg = THREADPOOL_MSG__UNDEFINED;
+
+ res = readn(thread->pipes.ack[0], &msg, sizeof(msg));
+ if (res < 0) {
+ pr_debug2("threadpool: failed to recv msg from tid=%d: %s\n",
+ thread->tid, strerror(errno));
+ return -THREADPOOL_ERROR__READPIPE;
+ }
+ if (msg != THREADPOOL_MSG__ACK) {
+ pr_debug2("threadpool: received unexpected msg from tid=%d: %s\n",
+ thread->tid, threadpool_msg_tags[msg]);
+ return -THREADPOOL_ERROR__INVALIDMSG;
+ }
+
+ pr_debug2("threadpool: received ack from tid=%d\n", thread->tid);
+
+ return 0;
+}
+
+/**
+ * threadpool__terminate_thread - send stop signal to thread and wait for ack
+ *
+ * NB: call only from main thread!
+ */
+static int threadpool__terminate_thread(struct threadpool_entry *thread)
+{
+ int res;
+ enum threadpool_msg msg = THREADPOOL_MSG__STOP;
+
+ res = writen(thread->pipes.cmd[1], &msg, sizeof(msg));
+ if (res < 0) {
+ pr_debug2("threadpool: error sending stop msg to tid=%d: %s\n",
+ thread->tid, strerror(errno));
+ return -THREADPOOL_ERROR__WRITEPIPE;
+ }
+
+ return threadpool__wait_thread(thread);
+}
+
+/**
+ * threadpool_entry__function - send ack to main thread
+ */
+static int threadpool_entry__send_ack(struct threadpool_entry *thread)
+{
+ enum threadpool_msg msg = THREADPOOL_MSG__ACK;
+ int ret = writen(thread->pipes.ack[1], &msg, sizeof(msg));
+
+ if (ret < 0) {
+ pr_debug("threadpool[%d]: failed to send ack: %s\n",
+ thread->tid, strerror(errno));
+ return -THREADPOOL_ERROR__WRITEPIPE;
+ }
+
+ return 0;
+}
+
+/**
+ * threadpool_entry__recv_cmd - receive command from main thread
+ */
+static int threadpool_entry__recv_cmd(struct threadpool_entry *thread,
+ enum threadpool_msg *cmd)
+{
+ int ret;
+
+ *cmd = THREADPOOL_MSG__UNDEFINED;
+ ret = readn(thread->pipes.cmd[0], cmd, sizeof(*cmd));
+ if (ret < 0) {
+ pr_debug("threadpool[%d]: error receiving command: %s\n",
+ thread->tid, strerror(errno));
+ return -THREADPOOL_ERROR__READPIPE;
+ }
+
+ if (*cmd != THREADPOOL_MSG__WAKE && *cmd != THREADPOOL_MSG__STOP) {
+ pr_debug("threadpool[%d]: received unexpected command: %s\n",
+ thread->tid, threadpool_msg_tags[*cmd]);
+ return -THREADPOOL_ERROR__INVALIDMSG;
+ }
+
+ return 0;
+}
+
+/**
+ * threadpool_entry__function - function running on thread
+ *
+ * This function waits for a signal from main thread to start executing
+ * a task.
+ * On completion, it will go back to sleep, waiting for another signal.
+ * Signals are delivered through pipes.
+ */
+static void *threadpool_entry__function(void *args)
+{
+ struct threadpool_entry *thread = (struct threadpool_entry *) args;
+ enum threadpool_msg cmd;
+
+ thread->tid = gettid();
+
+ pr_debug2("threadpool[%d]: started\n", thread->tid);
+
+ for (;;) {
+ if (threadpool_entry__send_ack(thread))
+ break;
+
+ if (threadpool_entry__recv_cmd(thread, &cmd))
+ break;
+
+ if (cmd == THREADPOOL_MSG__STOP)
+ break;
+ }
+
+ pr_debug2("threadpool[%d]: exit\n", thread->tid);
+
+ threadpool_entry__send_ack(thread);
+
+ return NULL;
+}
+
/**
* threadpool__new - create a fixed threadpool with @n_threads threads
*/
@@ -161,12 +326,30 @@ struct threadpool *threadpool__new(int n_threads)
*
* Buffer size should be at least THREADPOOL_STRERR_BUFSIZE bytes.
*/
-int threadpool__strerror(struct threadpool *pool __maybe_unused, int err, char *buf, size_t size)
+int threadpool__strerror(struct threadpool *pool, int err, char *buf, size_t size)
{
char sbuf[STRERR_BUFSIZE], *emsg;
+ const char *status_str, *errno_str;

- emsg = str_error_r(err, sbuf, sizeof(sbuf));
- return scnprintf(buf, size, "Error: %s.\n", emsg);
+ status_str = IS_ERR_OR_NULL(pool) ? "error" : threadpool_status_tags[pool->status];
+
+ switch (err) {
+ case -THREADPOOL_ERROR__SIGPROCMASK:
+ case -THREADPOOL_ERROR__READPIPE:
+ case -THREADPOOL_ERROR__WRITEPIPE:
+ emsg = str_error_r(errno, sbuf, sizeof(sbuf));
+ errno_str = threadpool_errno_str[-err-THREADPOOL_ERROR__OFFSET];
+ return scnprintf(buf, size, "%s: %s.\n", errno_str, emsg);
+ case -THREADPOOL_ERROR__INVALIDMSG:
+ errno_str = threadpool_errno_str[-err-THREADPOOL_ERROR__OFFSET];
+ return scnprintf(buf, size, "%s.\n", errno_str);
+ case -THREADPOOL_ERROR__NOTALLOWED:
+ return scnprintf(buf, size, "%s (%s).\n",
+ threadpool_errno_str[-err], status_str);
+ default:
+ emsg = str_error_r(err, sbuf, sizeof(sbuf));
+ return scnprintf(buf, size, "Error: %s", emsg);
+ }
}

/**
@@ -206,3 +389,142 @@ int threadpool__size(struct threadpool *pool)
{
return pool->nr_threads;
}
+
+/**
+ * __threadpool__start - start all threads in the pool.
+ *
+ * NB: use threadpool_start. This function does not change @pool->status.
+ */
+static int __threadpool__start(struct threadpool *pool)
+{
+ int t, tt, ret, err = 0, nr_threads = pool->nr_threads;
+ sigset_t full, mask;
+ pthread_t handle;
+ pthread_attr_t attrs;
+
+ sigfillset(&full);
+ if (sigprocmask(SIG_SETMASK, &full, &mask)) {
+ pr_debug2("Failed to block signals on threads start: %s\n", strerror(errno));
+ return -THREADPOOL_ERROR__SIGPROCMASK;
+ }
+
+ pthread_attr_init(&attrs);
+ pthread_attr_setdetachstate(&attrs, PTHREAD_CREATE_DETACHED);
+
+ for (t = 0; t < nr_threads; t++) {
+ struct threadpool_entry *thread = &pool->threads[t];
+
+ ret = pthread_create(&handle, &attrs, threadpool_entry__function, thread);
+ if (ret) {
+ err = ret;
+ pr_debug2("Failed to start threads: %s\n", strerror(errno));
+ break;
+ }
+ }
+
+ /**
+ * Wait for all threads that we managed to run.
+ * In case of further errors, continue to terminate possibly not
+ * failing threads.
+ */
+ for (tt = 0; tt < t; tt++) {
+ struct threadpool_entry *thread = &pool->threads[tt];
+
+ ret = threadpool__wait_thread(thread);
+ if (ret)
+ err = ret;
+ }
+
+ /**
+ * In case of errors, terminate all threads that we managed to run.
+ */
+ if (err) {
+ for (tt = 0; tt < t; tt++)
+ threadpool__terminate_thread(&pool->threads[tt]);
+ }
+
+ pthread_attr_destroy(&attrs);
+
+ if (sigprocmask(SIG_SETMASK, &mask, NULL)) {
+ pr_debug2("Failed to unblock signals on threads start: %s\n", strerror(errno));
+ err = -THREADPOOL_ERROR__SIGPROCMASK;
+ }
+
+ return err;
+}
+
+/**
+ * threadpool__start - start all threads in the pool.
+ *
+ * The function blocks until all threads are up and running.
+ */
+int threadpool__start(struct threadpool *pool)
+{
+ int ret;
+
+ if (pool->status != THREADPOOL_STATUS__STOPPED) {
+ pr_debug2("threadpool: starting not stopped pool\n");
+ return -THREADPOOL_ERROR__NOTALLOWED;
+ }
+
+ ret = __threadpool__start(pool);
+ if (ret) {
+ pool->status = THREADPOOL_STATUS__ERROR;
+ return ret;
+ }
+ pool->status = THREADPOOL_STATUS__READY;
+ return 0;
+}
+
+/**
+ * __threadpool__stop - stop all threads in the pool.
+ *
+ * NB: use threadpool_stop. This function does not change @pool->status.
+ */
+static int __threadpool__stop(struct threadpool *pool)
+{
+ int t, ret, err = 0;
+
+ for (t = 0; t < pool->nr_threads; t++) {
+ /**
+ * Even if a termination fails, we should continue to terminate
+ * all other threads.
+ */
+ ret = threadpool__terminate_thread(&pool->threads[t]);
+ if (ret)
+ err = ret;
+ }
+
+ return err;
+}
+
+/**
+ * threadpool__stop - stop all threads in the pool.
+ *
+ * This function blocks waiting for ack from all threads.
+ */
+int threadpool__stop(struct threadpool *pool)
+{
+ int ret;
+
+ if (pool->status != THREADPOOL_STATUS__READY) {
+ pr_debug2("threadpool: stopping not ready pool\n");
+ return -THREADPOOL_ERROR__NOTALLOWED;
+ }
+
+ ret = __threadpool__stop(pool);
+ if (ret) {
+ pool->status = THREADPOOL_STATUS__ERROR;
+ return ret;
+ }
+ pool->status = THREADPOOL_STATUS__STOPPED;
+ return 0;
+}
+
+/**
+ * threadpool__is_ready - check if the threads are running
+ */
+bool threadpool__is_ready(struct threadpool *pool)
+{
+ return pool->status == THREADPOOL_STATUS__READY;
+}
diff --git a/tools/perf/util/workqueue/threadpool.h b/tools/perf/util/workqueue/threadpool.h
index fb18aa32fb64f671..7d56e5450fac605b 100644
--- a/tools/perf/util/workqueue/threadpool.h
+++ b/tools/perf/util/workqueue/threadpool.h
@@ -21,9 +21,18 @@ extern int threadpool__execute(struct threadpool *pool, struct task_struct *task
extern int threadpool__wait(struct threadpool *pool);

extern int threadpool__size(struct threadpool *pool);
+extern bool threadpool__is_ready(struct threadpool *pool);

/* Error management */
#define THREADPOOL_STRERR_BUFSIZE (128+STRERR_BUFSIZE)
+#define THREADPOOL_ERROR__OFFSET 512
+enum {
+ THREADPOOL_ERROR__SIGPROCMASK = THREADPOOL_ERROR__OFFSET,
+ THREADPOOL_ERROR__READPIPE,
+ THREADPOOL_ERROR__WRITEPIPE,
+ THREADPOOL_ERROR__INVALIDMSG,
+ THREADPOOL_ERROR__NOTALLOWED
+};
extern int threadpool__strerror(struct threadpool *pool, int err, char *buf, size_t size);
extern int threadpool__new_strerror(struct threadpool *err_ptr, char *buf, size_t size);

--
2.31.1



2021-08-07 02:45:14

by Namhyung Kim

[permalink] [raw]
Subject: Re: [RFC PATCH v2 03/10] perf workqueue: add threadpool start and stop functions

On Fri, Jul 30, 2021 at 8:34 AM Riccardo Mancini <[email protected]> wrote:
>
> This patch adds the start and stop functions, alongside the thread
> function.
> Each thread will run until a stop signal is received.
> Furthermore, start and stop are added to the test.
>
> Thread management is based on the prototype from Alexey:
> https://lore.kernel.org/lkml/[email protected]/
>
> Suggested-by: Alexey Bayduraev <[email protected]>
> Signed-off-by: Riccardo Mancini <[email protected]>
> ---

[SNIP]
> @@ -93,6 +134,130 @@ static void threadpool_entry__close_pipes(struct threadpool_entry *thread)
> }
> }
>
> +/**
> + * threadpool__wait_thread - receive ack from thread
> + *
> + * NB: call only from main thread!
> + */
> +static int threadpool__wait_thread(struct threadpool_entry *thread)

If you wanted to differentiate APIs for main thread, I think it's better
to pass the pool struct (according to the name) and the index like:

int threadpool__wait_thread(struct threadpool *pool, int idx)

Then it can get a pointer to the entry easily.

> +{
> + int res;
> + enum threadpool_msg msg = THREADPOOL_MSG__UNDEFINED;
> +
> + res = readn(thread->pipes.ack[0], &msg, sizeof(msg));
> + if (res < 0) {
> + pr_debug2("threadpool: failed to recv msg from tid=%d: %s\n",
> + thread->tid, strerror(errno));
> + return -THREADPOOL_ERROR__READPIPE;
> + }
> + if (msg != THREADPOOL_MSG__ACK) {
> + pr_debug2("threadpool: received unexpected msg from tid=%d: %s\n",
> + thread->tid, threadpool_msg_tags[msg]);
> + return -THREADPOOL_ERROR__INVALIDMSG;
> + }
> +
> + pr_debug2("threadpool: received ack from tid=%d\n", thread->tid);
> +
> + return 0;
> +}
> +
> +/**
> + * threadpool__terminate_thread - send stop signal to thread and wait for ack
> + *
> + * NB: call only from main thread!
> + */
> +static int threadpool__terminate_thread(struct threadpool_entry *thread)

Ditto.

> +{
> + int res;
> + enum threadpool_msg msg = THREADPOOL_MSG__STOP;
> +
> + res = writen(thread->pipes.cmd[1], &msg, sizeof(msg));
> + if (res < 0) {
> + pr_debug2("threadpool: error sending stop msg to tid=%d: %s\n",
> + thread->tid, strerror(errno));
> + return -THREADPOOL_ERROR__WRITEPIPE;
> + }
> +
> + return threadpool__wait_thread(thread);
> +}
> +

[SNIP]
> @@ -161,12 +326,30 @@ struct threadpool *threadpool__new(int n_threads)
> *
> * Buffer size should be at least THREADPOOL_STRERR_BUFSIZE bytes.
> */
> -int threadpool__strerror(struct threadpool *pool __maybe_unused, int err, char *buf, size_t size)
> +int threadpool__strerror(struct threadpool *pool, int err, char *buf, size_t size)
> {
> char sbuf[STRERR_BUFSIZE], *emsg;
> + const char *status_str, *errno_str;
>
> - emsg = str_error_r(err, sbuf, sizeof(sbuf));
> - return scnprintf(buf, size, "Error: %s.\n", emsg);
> + status_str = IS_ERR_OR_NULL(pool) ? "error" : threadpool_status_tags[pool->status];
> +
> + switch (err) {
> + case -THREADPOOL_ERROR__SIGPROCMASK:
> + case -THREADPOOL_ERROR__READPIPE:
> + case -THREADPOOL_ERROR__WRITEPIPE:
> + emsg = str_error_r(errno, sbuf, sizeof(sbuf));
> + errno_str = threadpool_errno_str[-err-THREADPOOL_ERROR__OFFSET];
> + return scnprintf(buf, size, "%s: %s.\n", errno_str, emsg);
> + case -THREADPOOL_ERROR__INVALIDMSG:
> + errno_str = threadpool_errno_str[-err-THREADPOOL_ERROR__OFFSET];
> + return scnprintf(buf, size, "%s.\n", errno_str);
> + case -THREADPOOL_ERROR__NOTALLOWED:
> + return scnprintf(buf, size, "%s (%s).\n",
> + threadpool_errno_str[-err], status_str);

s/-err/-err-THREADPOOL_ERROR__OFFSET/ ?

It'd be nice if you calculate the index once.

> + default:
> + emsg = str_error_r(err, sbuf, sizeof(sbuf));

I'm confused whether the 'err' is negative or positive?

Thanks,
Namhyung


> + return scnprintf(buf, size, "Error: %s", emsg);
> + }
> }
>

2021-08-09 10:50:53

by Riccardo Mancini

[permalink] [raw]
Subject: Re: [RFC PATCH v2 03/10] perf workqueue: add threadpool start and stop functions

Hi,

On Fri, 2021-08-06 at 19:43 -0700, Namhyung Kim wrote:
> On Fri, Jul 30, 2021 at 8:34 AM Riccardo Mancini <[email protected]> wrote:
> >
> > This patch adds the start and stop functions, alongside the thread
> > function.
> > Each thread will run until a stop signal is received.
> > Furthermore, start and stop are added to the test.
> >
> > Thread management is based on the prototype from Alexey:
> > https://lore.kernel.org/lkml/[email protected]/
> >
> > Suggested-by: Alexey Bayduraev <[email protected]>
> > Signed-off-by: Riccardo Mancini <[email protected]>
> > ---
>
> [SNIP]
> > @@ -93,6 +134,130 @@ static void threadpool_entry__close_pipes(struct
> > threadpool_entry *thread)
> >         }
> >  }
> >
> > +/**
> > + * threadpool__wait_thread - receive ack from thread
> > + *
> > + * NB: call only from main thread!
> > + */
> > +static int threadpool__wait_thread(struct threadpool_entry *thread)
>
> If you wanted to differentiate APIs for main thread, I think it's better
> to pass the pool struct (according to the name) and the index like:
>
>   int threadpool__wait_thread(struct threadpool *pool, int idx)
>
> Then it can get a pointer to the entry easily.

Agree. 
I also need to more clearly separate those APIs too.

>
> > +{
> > +       int res;
> > +       enum threadpool_msg msg = THREADPOOL_MSG__UNDEFINED;
> > +
> > +       res = readn(thread->pipes.ack[0], &msg, sizeof(msg));
> > +       if (res < 0) {
> > +               pr_debug2("threadpool: failed to recv msg from tid=%d:
> > %s\n",
> > +                      thread->tid, strerror(errno));
> > +               return -THREADPOOL_ERROR__READPIPE;
> > +       }
> > +       if (msg != THREADPOOL_MSG__ACK) {
> > +               pr_debug2("threadpool: received unexpected msg from tid=%d:
> > %s\n",
> > +                      thread->tid, threadpool_msg_tags[msg]);
> > +               return -THREADPOOL_ERROR__INVALIDMSG;
> > +       }
> > +
> > +       pr_debug2("threadpool: received ack from tid=%d\n", thread->tid);
> > +
> > +       return 0;
> > +}
> > +
> > +/**
> > + * threadpool__terminate_thread - send stop signal to thread and wait for
> > ack
> > + *
> > + * NB: call only from main thread!
> > + */
> > +static int threadpool__terminate_thread(struct threadpool_entry *thread)
>
> Ditto.

ack

>
> > +{
> > +       int res;
> > +       enum threadpool_msg msg = THREADPOOL_MSG__STOP;
> > +
> > +       res = writen(thread->pipes.cmd[1], &msg, sizeof(msg));
> > +       if (res < 0) {
> > +               pr_debug2("threadpool: error sending stop msg to tid=%d:
> > %s\n",
> > +                       thread->tid, strerror(errno));
> > +               return -THREADPOOL_ERROR__WRITEPIPE;
> > +       }
> > +
> > +       return threadpool__wait_thread(thread);
> > +}
> > +
>
> [SNIP]
> > @@ -161,12 +326,30 @@ struct threadpool *threadpool__new(int n_threads)
> >   *
> >   * Buffer size should be at least THREADPOOL_STRERR_BUFSIZE bytes.
> >   */
> > -int threadpool__strerror(struct threadpool *pool __maybe_unused, int err,
> > char *buf, size_t size)
> > +int threadpool__strerror(struct threadpool *pool, int err, char *buf,
> > size_t size)
> >  {
> >         char sbuf[STRERR_BUFSIZE], *emsg;
> > +       const char *status_str, *errno_str;
> >
> > -       emsg = str_error_r(err, sbuf, sizeof(sbuf));
> > -       return scnprintf(buf, size, "Error: %s.\n", emsg);
> > +       status_str = IS_ERR_OR_NULL(pool) ? "error" :
> > threadpool_status_tags[pool->status];
> > +
> > +       switch (err) {
> > +       case -THREADPOOL_ERROR__SIGPROCMASK:
> > +       case -THREADPOOL_ERROR__READPIPE:
> > +       case -THREADPOOL_ERROR__WRITEPIPE:
> > +               emsg = str_error_r(errno, sbuf, sizeof(sbuf));
> > +               errno_str = threadpool_errno_str[-err-
> > THREADPOOL_ERROR__OFFSET];
> > +               return scnprintf(buf, size, "%s: %s.\n", errno_str, emsg);
> > +       case -THREADPOOL_ERROR__INVALIDMSG:
> > +               errno_str = threadpool_errno_str[-err-
> > THREADPOOL_ERROR__OFFSET];
> > +               return scnprintf(buf, size, "%s.\n", errno_str);
> > +       case -THREADPOOL_ERROR__NOTALLOWED:
> > +               return scnprintf(buf, size, "%s (%s).\n",
> > +                       threadpool_errno_str[-err], status_str);
>
> s/-err/-err-THREADPOOL_ERROR__OFFSET/ ?
>
> It'd be nice if you calculate the index once.

agreed

>
> > +       default:
> > +               emsg = str_error_r(err, sbuf, sizeof(sbuf));
>
> I'm confused whether the 'err' is negative or positive?

It's negative, so it needs to be inverted in this case.

Thanks,
Riccardo

>
> Thanks,
> Namhyung
>
>
> > +               return scnprintf(buf, size, "Error: %s", emsg);
> > +       }
> >  }
> >