From 508138b7947291e4805f5b0e77e3a78e44b16e58 Mon Sep 17 00:00:00 2001
From: Vladimir Davydov <vdavydov@tarantool.org>
Date: Fri, 21 Oct 2022 13:38:51 +0300
Subject: [PATCH] fiber: initialize thread-local cord on demand
We're planning to introduce a basic C API for user read views (EE-only).
Like all other box C API functions, the new API functions will use the
existing box error C API for reporting errors. The problem is that
a read view created using C API should be usable from user threads
(started with the pthread lib) while the box error C API doesn't work
in user threads, because those threads don't have the cord pointer
initialized (a diagnostic area is stored in a cord object).
To address this issue, let's create a new cord object automatically on
first use of cord() if it wasn't created explicitly. Automatically
created object is destroyed at thread exit (to achieve that, we use
the C++ RAII concept).
Closes #7814
NO_DOC=The C API documentation doesn't say anything about threads.
Let's keep it this way for now. We're planning to introduce
a new C API to work with threads in C modules. We'll update
the doc when it's ready.
---
.../unreleased/gh-7814-box-error-in-thread.md | 4 ++
src/lib/core/CMakeLists.txt | 1 +
src/lib/core/cord_on_demand.cc | 53 +++++++++++++++++++
src/lib/core/cord_on_demand.h | 25 +++++++++
src/lib/core/fiber.c | 2 +-
src/lib/core/fiber.h | 15 +++++-
test/unit/error.c | 39 +++++++++++++-
7 files changed, 136 insertions(+), 3 deletions(-)
create mode 100644 changelogs/unreleased/gh-7814-box-error-in-thread.md
create mode 100644 src/lib/core/cord_on_demand.cc
create mode 100644 src/lib/core/cord_on_demand.h
diff --git a/changelogs/unreleased/gh-7814-box-error-in-thread.md b/changelogs/unreleased/gh-7814-box-error-in-thread.md
new file mode 100644
index 0000000000..eb1026fa32
--- /dev/null
+++ b/changelogs/unreleased/gh-7814-box-error-in-thread.md
@@ -0,0 +1,4 @@
+## feature/core
+
+* The box error C API (`box_error_set()`, `box_error_last()`, etc) can now be
+ used in threads started by user modules with the pthread library (gh-7814).
diff --git a/src/lib/core/CMakeLists.txt b/src/lib/core/CMakeLists.txt
index 8c0ee829a2..9aff018f74 100644
--- a/src/lib/core/CMakeLists.txt
+++ b/src/lib/core/CMakeLists.txt
@@ -43,6 +43,7 @@ set(core_sources
tt_sigaction.c
tt_strerror.c
mp_util.c
+ cord_on_demand.cc
)
if (ENABLE_BACKTRACE)
diff --git a/src/lib/core/cord_on_demand.cc b/src/lib/core/cord_on_demand.cc
new file mode 100644
index 0000000000..a47b3b313e
--- /dev/null
+++ b/src/lib/core/cord_on_demand.cc
@@ -0,0 +1,53 @@
+/*
+ * SPDX-License-Identifier: BSD-2-Clause
+ *
+ * Copyright 2010-2022, Tarantool AUTHORS, please see AUTHORS file.
+ */
+
+#include "cord_on_demand.h"
+
+#include <stdlib.h>
+
+#include "fiber.h"
+#include "trivia/util.h"
+
+/**
+ * RAII wrapper around a cord object.
+ *
+ * A thread-local cord object is created on the first call to the get() method
+ * and destroyed when the thread exits.
+ */
+class CordOnDemand final {
+public:
+ static cord *get() noexcept
+ {
+ thread_local CordOnDemand singleton;
+ return singleton.cord_ptr;
+ }
+
+private:
+ struct cord *cord_ptr;
+
+ CordOnDemand() noexcept
+ {
+ cord_ptr = static_cast<struct cord *>(
+ xcalloc(1, sizeof(*cord_ptr)));
+ cord_create(cord_ptr, "unknown");
+ }
+
+ ~CordOnDemand()
+ {
+ cord_exit(cord_ptr);
+ cord_destroy(cord_ptr);
+ free(cord_ptr);
+ }
+
+ CordOnDemand(CordOnDemand &other) = delete;
+ CordOnDemand &operator=(CordOnDemand &other) = delete;
+};
+
+struct cord *
+cord_on_demand(void)
+{
+ return CordOnDemand::get();
+}
diff --git a/src/lib/core/cord_on_demand.h b/src/lib/core/cord_on_demand.h
new file mode 100644
index 0000000000..c0491c7341
--- /dev/null
+++ b/src/lib/core/cord_on_demand.h
@@ -0,0 +1,25 @@
+/*
+ * SPDX-License-Identifier: BSD-2-Clause
+ *
+ * Copyright 2010-2022, Tarantool AUTHORS, please see AUTHORS file.
+ */
+
+#pragma once
+
+#ifdef __cplusplus
+extern "C" {
+#endif /* __cplusplus */
+
+struct cord;
+
+/**
+ * On the first call, creates and returns a new thread-local cord object.
+ * On all subsequent calls in the same thread, returns the object created
+ * earlier. The cord object is destroyed at thread exit.
+ */
+struct cord *
+cord_on_demand(void);
+
+#ifdef __cplusplus
+} /* extern "C" */
+#endif /* __cplusplus */
diff --git a/src/lib/core/fiber.c b/src/lib/core/fiber.c
index d8ccac4f9f..aceb2c7520 100644
--- a/src/lib/core/fiber.c
+++ b/src/lib/core/fiber.c
@@ -1481,7 +1481,7 @@ box_region_truncate(size_t size)
void
cord_create(struct cord *cord, const char *name)
{
- cord() = cord;
+ cord_ptr = cord;
slab_cache_set_thread(&cord()->slabc);
cord->id = pthread_self();
diff --git a/src/lib/core/fiber.h b/src/lib/core/fiber.h
index 282c732448..694cebb602 100644
--- a/src/lib/core/fiber.h
+++ b/src/lib/core/fiber.h
@@ -36,6 +36,7 @@
#include <stdint.h>
#include "tt_pthread.h"
#include <tarantool_ev.h>
+#include "cord_on_demand.h"
#include "diag.h"
#include "trivia/util.h"
#include "small/mempool.h"
@@ -783,7 +784,19 @@ struct cord {
extern __thread struct cord *cord_ptr;
-#define cord() cord_ptr
+/**
+ * Returns a thread-local cord object.
+ *
+ * If the cord object wasn't initialized at thread start (cord_create()
+ * wasn't called), a cord object is created automatically and destroyed
+ * at thread exit.
+ */
+#define cord() ({ \
+ if (unlikely(cord_ptr == NULL)) \
+ cord_ptr = cord_on_demand(); \
+ cord_ptr; \
+})
+
#define fiber() cord()->fiber
#define loop() (cord()->loop)
diff --git a/test/unit/error.c b/test/unit/error.c
index 9bed7df07d..b1f5e908e0 100644
--- a/test/unit/error.c
+++ b/test/unit/error.c
@@ -18,6 +18,7 @@
#include "unit.h"
#include <float.h>
+#include <pthread.h>
static void
test_payload_field_str(void)
@@ -481,11 +482,46 @@ test_error_code(void)
footer();
}
+static void *
+test_pthread_f(void *arg)
+{
+ (void)arg;
+ is(box_error_last(), NULL, "last error before set");
+ box_error_raise(ER_ILLEGAL_PARAMS, "Test %d", 42);
+ box_error_t *err = box_error_last();
+ isnt(err, NULL, "last error after set");
+ is(strcmp(box_error_type(err), "ClientError"), 0, "last error type");
+ is(box_error_code(err), ER_ILLEGAL_PARAMS, "last error code");
+ is(strcmp(box_error_message(err), "Test 42"), 0, "last error message");
+ box_error_clear();
+ is(box_error_last(), NULL, "last error after clear");
+ return NULL;
+}
+
+static void
+test_pthread(void)
+{
+ header();
+ plan(6);
+
+ pthread_attr_t attr;
+ fail_unless(pthread_attr_init(&attr) == 0);
+ fail_unless(pthread_attr_setdetachstate(
+ &attr, PTHREAD_CREATE_JOINABLE) == 0);
+
+ pthread_t thread;
+ fail_unless(pthread_create(&thread, &attr, test_pthread_f, NULL) == 0);
+ fail_unless(pthread_join(thread, NULL) == 0);
+
+ check_plan();
+ footer();
+}
+
int
main(void)
{
header();
- plan(10);
+ plan(11);
random_init();
memory_init();
@@ -501,6 +537,7 @@ main(void)
test_payload_clear();
test_payload_move();
test_error_code();
+ test_pthread();
fiber_free();
memory_free();
--
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