From: Waldemar Kozaczuk <jwkozac...@gmail.com>
Committer: Nadav Har'El <n...@scylladb.com>
Branch: master
semaphores: fix sem_trywait
This patch fixes a subtle but critical bug in sem_trywait()
underlying implementation (semaphore.cc) which
for example prevented new version of Java 12 and above
hang on startup in infinite loop.
It also adds new unit test around sem_* functions.
Signed-off-by: Waldemar Kozaczuk <jwkozac...@gmail.com>
Message-Id: <20190810040911.13897-1-jwkozac...@gmail.com>
---
diff --git a/core/semaphore.cc b/core/semaphore.cc
--- a/core/semaphore.cc
+++ b/core/semaphore.cc
@@ -62,7 +62,7 @@ bool semaphore::trywait(unsigned units)
{
bool ok = false;
WITH_LOCK(_mtx) {
- if (_val > units) {
+ if (_val >= units) {
_val -= units;
ok = true;
}
diff --git a/modules/tests/Makefile b/modules/tests/Makefile
--- a/modules/tests/Makefile
+++ b/modules/tests/Makefile
@@ -128,7 +128,7 @@ tests := tst-pthread.so misc-ramdisk.so tst-vblk.so
tst-bsd-evh.so \
tst-ttyname.so tst-pthread-barrier.so tst-feexcept.so tst-math.so \
tst-sigaltstack.so tst-fread.so tst-tcp-cork.so tst-tcp-v6.so \
tst-calloc.so tst-crypt.so tst-non-fpic.so tst-small-malloc.so \
- tst-mmx-fpu.so tst-getopt.so tst-getopt-pie.so tst-non-pie.so
+ tst-mmx-fpu.so tst-getopt.so tst-getopt-pie.so tst-non-pie.so
tst-semaphore.so
# libstatic-thread-variable.so tst-static-thread-variable.so \
tests += testrunner.so
diff --git a/tests/tst-semaphore.c b/tests/tst-semaphore.c
--- a/tests/tst-semaphore.c
+++ b/tests/tst-semaphore.c
@@ -0,0 +1,59 @@
+/*
+ * Copyright (C) 2019 Waldemar Kozaczuk
+ *
+ * This work is open source software, licensed under the terms of the
+ * BSD license as described in the LICENSE file in the top-level directory.
+ */
+#include <stdio.h>
+#include <string.h>
+#include <stdlib.h>
+#include <pthread.h>
+#include <unistd.h>
+#include <semaphore.h>
+#include <assert.h>
+
+#define THREAD_NUMBER 10
+
+static sem_t sem_sync, sem_done;
+static int counter = 0;
+
+static void* threadfunc(void* arg) {
+ int *thread_number = (int*)arg;
+ for (int i = 0; i < 10; i++) {
+ assert(sem_wait(&sem_sync) == 0);
+ counter++;
+ assert(sem_post(&sem_sync) == 0);
+ printf("Thread %d: Incremented %dth\n", *thread_number, i + 1);
+ usleep(1000 * (counter % 5)); // Pseudo-randomly sleep between
0-4ms
+ }
+ assert(sem_post(&sem_done) == 0);
+ return NULL;
+}
+
+int main(void) {
+ pthread_t threads[THREAD_NUMBER];
+ int threads_numbers[THREAD_NUMBER];
+
+ assert(sem_init(&sem_sync, 0, 1) == 0);
+ assert(sem_init(&sem_done, 0, 0) == 0);
+
+ for (int t = 0; t < THREAD_NUMBER; t++) {
+ threads_numbers[t] = t + 1;
+ pthread_create(threads + t, NULL, &threadfunc, threads_numbers +
t);
+ }
+
+ for (int t = 0; t < THREAD_NUMBER; t++) {
+ while(sem_trywait(&sem_done));
+ }
+
+ assert(counter == 10 * THREAD_NUMBER);
+
+ for (int t = 0; t < THREAD_NUMBER; t++) {
+ pthread_join(threads[t], NULL);
+ }
+
+ assert(sem_destroy(&sem_sync) == 0);
+ assert(sem_destroy(&sem_done) == 0);
+
+ return 0;
+}
--
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