FIX #294: make OpenBLAS thread-pool resilient to fork via pthread_atfork

driver/others/blas_server.c

@@ -74,6 +74,21 @@ USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 #include <sys/resource.h>
 #endif
 
+#ifndef likely
+#ifdef __GNUC__
+#define likely(x) __builtin_expect(!!(x), 1)
+#else
+#define likely(x) (x)
+#endif
+#endif
+#ifndef unlikely
+#ifdef __GNUC__
+#define unlikely(x) __builtin_expect(!!(x), 0)
+#else
+#define unlikely(x) (x)
+#endif
+#endif
+
 #ifdef SMP_SERVER
 
 #undef MONITOR
@@ -584,6 +599,10 @@ static BLASULONG exec_queue_lock = 0;
 
 int exec_blas_async(BLASLONG pos, blas_queue_t *queue){
 
+#ifdef SMP_SERVER
+  // Handle lazy re-init of the thread-pool after a POSIX fork
+  if (unlikely(blas_server_avail == 0)) blas_thread_init();
+#endif
   BLASLONG i = 0;
   blas_queue_t *current = queue;
 #if defined(OS_LINUX) && !defined(NO_AFFINITY) && !defined(PARAMTEST)
@@ -708,7 +727,11 @@ int exec_blas_async_wait(BLASLONG num, blas_queue_t *queue){
 /* Execute Threads */
 int exec_blas(BLASLONG num, blas_queue_t *queue){
 
-   int (*routine)(blas_arg_t *, void *, void *, double *, double *, BLASLONG);
+#ifdef SMP_SERVER
+  // Handle lazy re-init of the thread-pool after a POSIX fork
+  if (unlikely(blas_server_avail == 0)) blas_thread_init();
+#endif
+  int (*routine)(blas_arg_t *, void *, void *, double *, double *, BLASLONG);
 
 #ifdef TIMING_DEBUG
   BLASULONG start, stop;

driver/others/memory.c

@@ -143,6 +143,8 @@ USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 gotoblas_t *gotoblas = NULL;
 #endif
 
+extern void openblas_warning(int verbose, const char * msg);
+
 #ifndef SMP
 
 #define blas_cpu_number 1
@@ -253,6 +255,21 @@ int  goto_get_num_procs  (void) {
   return blas_cpu_number;
 }
 
+void openblas_fork_handler()
+{
+  // This handler shuts down the OpenBLAS-managed PTHREAD pool when OpenBLAS is
+  // built with "make USE_OPENMP=0".
+  // Hanging can still happen when OpenBLAS is built against the libgomp
+  // implementation of OpenMP. The problem is tracked at:
+  //   http://gcc.gnu.org/bugzilla/show_bug.cgi?id=60035
+  // In the mean time build with USE_OPENMP=0 or link against another
+  // implementation of OpenMP.
+  int err;
+  err = pthread_atfork (BLASFUNC(blas_thread_shutdown), NULL, NULL);
+  if(err != 0)
+    openblas_warning(0, "OpenBLAS Warning ... cannot install fork handler. You may meet hang after fork.\n");
+}
+
 int blas_get_cpu_number(void){
   char *p;
 #if defined(OS_LINUX) || defined(OS_WINDOWS) || defined(OS_FREEBSD) || defined(OS_DARWIN)
@@ -1268,6 +1285,9 @@ void CONSTRUCTOR gotoblas_init(void) {
 
   if (gotoblas_initialized) return;
 
+#ifdef SMP
+  openblas_fork_handler();
+#endif
 
 #ifdef PROFILE
    moncontrol (0);

utest/Makefile

@@ -11,7 +11,7 @@ CUNIT_LIB=$(CUNIT_DIR)/lib/libcunit.a
 
 CFLAGS+=-I$(CUNIT_DIR)/include
 
-OBJS=main.o test_rot.o test_swap.o test_axpy.o test_dotu.o test_rotmg.o test_dsdot.o test_amax.o
+OBJS=main.o test_rot.o test_swap.o test_axpy.o test_dotu.o test_rotmg.o test_dsdot.o test_amax.o test_fork.o
 
 all : run_test
 

utest/common_utest.h

@@ -63,4 +63,6 @@ void test_dsdot_n_1(void);
 
 void test_samax(void);
 
+void test_fork_safety(void);
+
 #endif

utest/main.c

@@ -60,6 +60,14 @@ CU_TestInfo test_level1[]={
 	{"Testing dsdot with n == 1",test_dsdot_n_1},
 
 	{"Testing samax", test_samax},
+
+#if !defined(USE_OPENMP) && !defined(OS_WINDOWS)
+	// The GNU OpenMP implementation libgomp is not fork-safe (as of 4.8.2):
+	// http://gcc.gnu.org/bugzilla/show_bug.cgi?id=60035
+	// Hence skip this test when OpenBLAS is built with OpenMP.
+	{"Testing fork safety", test_fork_safety},
+#endif
+
 	CU_TEST_INFO_NULL,
 };
 

utest/test_fork.c

@@ -0,0 +1,122 @@
+/*****************************************************************************
+Copyright (c) 2014, Lab of Parallel Software and Computational Science,ICSAS
+All rights reserved.
+
+Redistribution and use in source and binary forms, with or without
+modification, are permitted provided that the following conditions are
+met:
+
+   1. Redistributions of source code must retain the above copyright
+      notice, this list of conditions and the following disclaimer.
+
+   2. Redistributions in binary form must reproduce the above copyright
+      notice, this list of conditions and the following disclaimer in
+      the documentation and/or other materials provided with the
+      distribution.
+   3. Neither the name of the ISCAS nor the names of its contributors may
+      be used to endorse or promote products derived from this software
+      without specific prior written permission.
+
+THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
+LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE
+USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+**********************************************************************************/
+
+#include "common_utest.h"
+#include <sys/wait.h>
+#include <cblas.h>
+
+void* xmalloc(size_t n)
+{
+    void* tmp;
+    tmp = malloc(n);
+    if (tmp == NULL) {
+        fprintf(stderr, "You are about to die\n");
+        exit(1);
+    } else {
+        return tmp;
+    }
+}
+
+void check_dgemm(double *a, double *b, double *result, double *expected, int n)
+{
+    int i;
+    cblas_dgemm(CblasRowMajor, CblasNoTrans, CblasNoTrans, n, n, n,
+        1.0, a, n, b, n, 0.0, result, n);
+    for(i = 0; i < n * n; ++i) {
+        CU_ASSERT_DOUBLE_EQUAL(expected[i], result[i], CHECK_EPS);
+    }
+}
+
+
+void test_fork_safety(void)
+{
+    int n = 1000;
+    int i;
+     
+    double *a, *b, *c, *d;
+    size_t n_bytes;
+     
+    pid_t fork_pid;
+    pid_t fork_pid_nested;
+
+    n_bytes = sizeof(*a) * n * n;
+     
+    a = xmalloc(n_bytes);
+    b = xmalloc(n_bytes);
+    c = xmalloc(n_bytes);
+    d = xmalloc(n_bytes);
+    
+    // Put ones in a and b
+    for(i = 0; i < n * n; ++i) {
+        a[i] = 1;
+        b[i] = 1;
+    }
+
+    // Compute a DGEMM product in the parent process prior to forking to
+    // ensure that the OpenBLAS thread pool is initialized.
+    cblas_dgemm(CblasRowMajor, CblasNoTrans, CblasNoTrans, n, n, n,
+       1.0, a, n, b, n, 0.0, c, n);
+
+    fork_pid = fork();
+    if (fork_pid == -1) {
+        CU_FAIL("Failed to fork process.");
+    } else if (fork_pid == 0) {
+        // Compute a DGEMM product in the child process to check that the
+        // thread pool as been properly been reinitialized after the fork.
+        check_dgemm(a, b, d, c, n);
+
+        // Nested fork to check that the pthread_atfork protection can work
+        // recursively
+        fork_pid_nested = fork();
+        if (fork_pid_nested == -1) {
+            CU_FAIL("Failed to fork process.");
+            exit(1);
+        } else if (fork_pid_nested == 0) {
+            check_dgemm(a, b, d, c, n);
+            exit(0);
+        } else {
+            check_dgemm(a, b, d, c, n);
+            int child_status = 0;
+            pid_t wait_pid = wait(&child_status);
+            CU_ASSERT(wait_pid == fork_pid_nested);
+            CU_ASSERT(WEXITSTATUS (child_status) == 0);
+            exit(0);
+        }
+    } else {
+        check_dgemm(a, b, d, c, n);
+        // Wait for the child to finish and check the exit code.
+        int child_status = 0;
+        pid_t wait_pid = wait(&child_status);
+        CU_ASSERT(wait_pid == fork_pid);
+        CU_ASSERT(WEXITSTATUS (child_status) == 0);
+    }
+}