Lakka-LibreELEC/packages/devel/tbb/patches/tbb-999.01-PR824-retry-if-pthread_create-fails-with-EAGAIN.patch

From 3a8bc6478654afcbd219f45e7ea01353c2d57eb6 Mon Sep 17 00:00:00 2001
From: Rui Ueyama <ruiu@cs.stanford.edu>
Date: Sat, 7 May 2022 19:55:24 +0800
Subject: [PATCH] Retry if pthread_create fails with EAGAIN

On many Unix-like systems, pthread_create can fail spuriously even if
the running machine has enough resources to spawn a new thread.
Therefore, if EAGAIN is returned from pthread_create, we actually have
to try again.

I observed this issue when running the mold linker
(https://github.com/rui314/mold) under a heavy load. mold uses OneTBB
for parallelization.

As another data point, Go has the same logic to retry on EAGAIN:
https://go-review.googlesource.com/c/go/+/33894/

nanosleep is defined in POSIX 2001, so I believe that all Unix-like
systems support it.

Signed-off-by: Rui Ueyama <ruiu@cs.stanford.edu>
---
 src/tbb/rml_thread_monitor.h     | 30 +++++++++++++++-
 test/CMakeLists.txt              |  3 ++
 test/tbb/test_pthread_create.cpp | 59 ++++++++++++++++++++++++++++++++
 3 files changed, 91 insertions(+), 1 deletion(-)
 create mode 100644 test/tbb/test_pthread_create.cpp

diff --git a/src/tbb/rml_thread_monitor.h b/src/tbb/rml_thread_monitor.h
index 13b556380..dc046ba00 100644
--- a/src/tbb/rml_thread_monitor.h
+++ b/src/tbb/rml_thread_monitor.h
@@ -31,6 +31,7 @@
 #include <pthread.h>
 #include <cstring>
 #include <cstdlib>
+#include <time.h>
 #else
 #error Unsupported platform
 #endif
@@ -183,6 +184,32 @@ inline void thread_monitor::check( int error_code, const char* routine ) {
     }
 }
 
+// pthread_create(2) can spuriously fail on Linux. This is a function
+// to wrap pthread_create(2) to retry if it fails with EAGAIN.
+inline void do_pthread_create(pthread_t *handle, pthread_attr_t *s, void* (*thread_routine)(void*), void* arg) {
+#ifdef __linux__
+  int tries = 0;
+  const int max_num_tries = 20;
+
+  for (;;) {
+    int error_code = pthread_create(handle, s, thread_routine, arg);
+    if (!error_code)
+      break;
+    if (error_code != EAGAIN || tries++ > max_num_tries) {
+      handle_perror(error_code, "pthread_create has failed");
+      break;
+    }
+
+    // Retry after tries * 1 millisecond.
+    struct timespec ts = {0, tries * 1000 * 1000};
+    nanosleep(&ts, NULL);
+  }
+#else
+  if (int error_code = pthread_create(handle, s, thread_routine, arg))
+    handle_perror(error_code, "pthread_create has failed");
+#endif
+}
+
 inline thread_monitor::handle_type thread_monitor::launch( void* (*thread_routine)(void*), void* arg, std::size_t stack_size ) {
     // FIXME - consider more graceful recovery than just exiting if a thread cannot be launched.
     // Note that there are some tricky situations to deal with, such that the thread is already
@@ -191,8 +218,9 @@ inline thread_monitor::handle_type thread_monitor::launch( void* (*thread_routin
     check(pthread_attr_init( &s ), "pthread_attr_init has failed");
     if( stack_size>0 )
         check(pthread_attr_setstacksize( &s, stack_size ), "pthread_attr_setstack_size has failed" );
+
     pthread_t handle;
-    check( pthread_create( &handle, &s, thread_routine, arg ), "pthread_create has failed" );
+    do_pthread_create(&handle, &s, thread_routine, arg);
     check( pthread_attr_destroy( &s ), "pthread_attr_destroy has failed" );
     return handle;
 }
diff --git a/test/CMakeLists.txt b/test/CMakeLists.txt
index f15679e83..92802b015 100644
--- a/test/CMakeLists.txt
+++ b/test/CMakeLists.txt
@@ -373,6 +373,9 @@ if (TARGET TBB::tbb)
     if (APPLE OR ANDROID_PLATFORM)
         target_link_libraries(test_dynamic_link PRIVATE -rdynamic) # for the test_dynamic_link
     endif()
+    if (UNIX AND NOT APPLE)
+      tbb_add_test(SUBDIR tbb NAME test_pthread_create DEPENDENCIES TBB::tbb)
+    endif()
     tbb_add_test(SUBDIR tbb NAME test_collaborative_call_once DEPENDENCIES TBB::tbb)
     tbb_add_test(SUBDIR tbb NAME test_concurrent_lru_cache DEPENDENCIES TBB::tbb)
     tbb_add_test(SUBDIR tbb NAME test_concurrent_unordered_map DEPENDENCIES TBB::tbb)
diff --git a/test/tbb/test_pthread_create.cpp b/test/tbb/test_pthread_create.cpp
new file mode 100644
index 000000000..4cb1f4ea5
--- /dev/null
+++ b/test/tbb/test_pthread_create.cpp
@@ -0,0 +1,59 @@
+/*
+    Copyright (c) 2005-2022 Intel Corporation
+
+    Licensed under the Apache License, Version 2.0 (the "License");
+    you may not use this file except in compliance with the License.
+    You may obtain a copy of the License at
+
+        http://www.apache.org/licenses/LICENSE-2.0
+
+    Unless required by applicable law or agreed to in writing, software
+    distributed under the License is distributed on an "AS IS" BASIS,
+    WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+    See the License for the specific language governing permissions and
+    limitations under the License.
+*/
+
+#include "common/test.h"
+#include "common/utils.h"
+
+#include <atomic>
+#include <sys/types.h>
+#include <sys/wait.h>
+#include <tbb/global_control.h>
+#include <tbb/parallel_for.h>
+#include <thread>
+#include <unistd.h>
+
+//! Test that thread pool creation won't be affected with a spurious failure of pthread_create().
+//! \brief \ref error_guessing
+TEST_CASE("pthread_create is not affected by fork") {
+    std::atomic_bool done;
+
+    std::thread thr([&]() {
+        while (!done) {
+            pid_t pid = fork();
+            CHECK(pid != -1);
+
+            if (pid == 0) {
+                // child
+              _exit(0);
+            } else {
+                int wstatus;
+                do {
+                  pid_t pid2 = waitpid(pid, &wstatus, 0);
+                  CHECK(pid2 != -1);
+                } while (!WIFEXITED(wstatus) && !WIFSIGNALED(wstatus));
+            }
+        }
+    });
+
+    for (int i = 0; i < 50; i++) {
+        tbb::task_scheduler_handle handle{tbb::attach{}};
+        tbb::parallel_for(0, 10000, [](int) {});
+        tbb::finalize(handle);
+    }
+
+    done = true;
+    thr.join();
+}