return 0;
}
+/* The cached PID, possible values:
+ *
+ * == UNSET [0] → cache not initialized yet
+ * == BUSY [-1] → some thread is initializing it at the moment
+ * any other → the cached PID
+ */
+
+#define CACHED_PID_UNSET ((pid_t) 0)
+#define CACHED_PID_BUSY ((pid_t) -1)
+
+static pid_t cached_pid = CACHED_PID_UNSET;
+
+static void reset_cached_pid(void) {
+ /* Invoked in the child after a fork(), i.e. at the first moment the PID changed */
+ cached_pid = CACHED_PID_UNSET;
+}
+
+/* We use glibc __register_atfork() + __dso_handle directly here, as they are not included in the glibc
+ * headers. __register_atfork() is mostly equivalent to pthread_atfork(), but doesn't require us to link against
+ * libpthread, as it is part of glibc anyway. */
+extern int __register_atfork(void (*prepare) (void), void (*parent) (void), void (*child) (void), void * __dso_handle);
+extern void* __dso_handle __attribute__ ((__weak__));
+
+pid_t getpid_cached(void) {
+ pid_t current_value;
+
+ /* getpid_cached() is much like getpid(), but caches the value in local memory, to avoid having to invoke a
+ * system call each time. This restores glibc behaviour from before 2.24, when getpid() was unconditionally
+ * cached. Starting with 2.24 getpid() started to become prohibitively expensive when used for detecting when
+ * objects were used across fork()s. With this caching the old behaviour is somewhat restored.
+ *
+ * https://bugzilla.redhat.com/show_bug.cgi?id=1443976
+ * https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=1d2bc2eae969543b89850e35e532f3144122d80a
+ */
+
+ current_value = __sync_val_compare_and_swap(&cached_pid, CACHED_PID_UNSET, CACHED_PID_BUSY);
+
+ switch (current_value) {
+
+ case CACHED_PID_UNSET: { /* Not initialized yet, then do so now */
+ pid_t new_pid;
+
+ new_pid = getpid();
+
+ if (__register_atfork(NULL, NULL, reset_cached_pid, __dso_handle) != 0) {
+ /* OOM? Let's try again later */
+ cached_pid = CACHED_PID_UNSET;
+ return new_pid;
+ }
+
+ cached_pid = new_pid;
+ return new_pid;
+ }
+
+ case CACHED_PID_BUSY: /* Somebody else is currently initializing */
+ return getpid();
+
+ default: /* Properly initialized */
+ return current_value;
+ }
+}
+
static const char *const ioprio_class_table[] = {
[IOPRIO_CLASS_NONE] = "none",
[IOPRIO_CLASS_RT] = "realtime",
test_rename_process_one("1234567", 1); /* should always fit */
}
+static void test_getpid_cached(void) {
+ siginfo_t si;
+ pid_t a, b, c, d, e, f, child;
+
+ a = raw_getpid();
+ b = getpid_cached();
+ c = getpid();
+
+ assert_se(a == b && a == c);
+
+ child = fork();
+ assert_se(child >= 0);
+
+ if (child == 0) {
+ /* In child */
+ a = raw_getpid();
+ b = getpid_cached();
+ c = getpid();
+
+ assert_se(a == b && a == c);
+ _exit(0);
+ }
+
+ d = raw_getpid();
+ e = getpid_cached();
+ f = getpid();
+
+ assert_se(a == d && a == e && a == f);
+
+ assert_se(wait_for_terminate(child, &si) >= 0);
+ assert_se(si.si_status == 0);
+ assert_se(si.si_code == CLD_EXITED);
+}
+
+#define MEASURE_ITERATIONS (10000000LLU)
+
+static void test_getpid_measure(void) {
+ unsigned long long i;
+ usec_t t, q;
+
+ t = now(CLOCK_MONOTONIC);
+ for (i = 0; i < MEASURE_ITERATIONS; i++)
+ (void) getpid();
+ q = now(CLOCK_MONOTONIC) - t;
+
+ log_info(" glibc getpid(): %llu/s\n", (unsigned long long) (MEASURE_ITERATIONS*USEC_PER_SEC/q));
+
+ t = now(CLOCK_MONOTONIC);
+ for (i = 0; i < MEASURE_ITERATIONS; i++)
+ (void) getpid_cached();
+ q = now(CLOCK_MONOTONIC) - t;
+
+ log_info("getpid_cached(): %llu/s\n", (unsigned long long) (MEASURE_ITERATIONS*USEC_PER_SEC/q));
+}
+
int main(int argc, char *argv[]) {
log_set_max_level(LOG_DEBUG);
test_personality();
test_get_process_cmdline_harder();
test_rename_process();
+ test_getpid_cached();
+ test_getpid_measure();
return 0;
}