The following example proves that the man page
pthread_attr_setschedparam.3 is incorrect when it claims that the
pthread_attr_setschedparam function always succeeds on linux:
#include <pthread.h>
#include <errno.h>
int main() {
pthread_attr_t attr;
struct sched_param p = {-1}; /* invalid priority */
if (pthread_attr_init(&attr) == 0)
if (pthread_attr_setschedpolicy(&attr, SCHED_OTHER) == 0)
if (pthread_attr_setschedparam(&attr, &p) == EINVAL)
return 1;
return 0;
}
The program exits with exit code 1, therefore pthread_attr_setschedparam
has returned error code EINVAL.
I could evoke this error on ubuntu 14.04, and verify it by examining the
eglibc-2.19 source code. The function is implemented in file
fbtl/pthread_attr_setschedparam.c. For error checking, it calls the
helper function check_sched_priority_attr which is implemented inline in
file ./fbtl/pthreadP.h. This function returns EINVAL if a range check fails.
The attached patch corrects the man page. The patch is against the
current git master, 298f72af973e4bf3975d6a84369286b548e6fb63
diff --git a/man3/pthread_attr_setschedparam.3 b/man3/pthread_attr_setschedparam.3
index f3db870..8ea4f47 100644
--- a/man3/pthread_attr_setschedparam.3
+++ b/man3/pthread_attr_setschedparam.3
@@ -86,15 +86,22 @@ to
On success, these functions return 0;
on error, they return a nonzero error number.
.SH ERRORS
-POSIX.1 documents
+.BR pthread_attr_setschedparam ()
+can fail with the following error:
+.TP
.B EINVAL
-and
+the priority specified in
+.I param
+does not make sense for the current scheduling policy of
+.IR attr .
+.PP
+POSIX.1 also documents an
.B ENOTSUP
-errors for
+error for
.BR pthread_attr_setschedparam ().
-On Linux these functions always succeed
+This value is never returned on Linux
(but portable and future-proof applications should nevertheless
-handle a possible error return).
+handle this error return value).
.\" .SH VERSIONS
.\" Available since glibc 2.0.
.SH ATTRIBUTES
