[libc-commits] [libc] 6e25eae - [libc] Implement pthread_attr_[gs]etschedpolicy (#222682)
via libc-commits
libc-commits at lists.llvm.org
Fri Sep 11 01:54:53 PDT 2026
Author: Pavel Labath
Date: 2026-09-11T10:54:48+02:00
New Revision: 6e25eaedeee9ee4845565514dce823988ac7f23c
URL: https://github.com/llvm/llvm-project/commit/6e25eaedeee9ee4845565514dce823988ac7f23c
DIFF: https://github.com/llvm/llvm-project/commit/6e25eaedeee9ee4845565514dce823988ac7f23c.diff
LOG: [libc] Implement pthread_attr_[gs]etschedpolicy (#222682)
This patch implements pthread_attr_setschedpolicy and
pthread_attr_getschedpolicy.
This commit only operates on the pthread_attr_t object. It does not
attempt to install the scheduling policy when creating a new thread. I'm
leaving that for a separate patch as it requires a moderately
complicated startup dance to ensure that the scheduling policy takes
effect before the startup code runs.
The validation of inputs in pthread_attr_setschedpolicy is an
interesting question. Glibc accepts only policies explicitly declared in
POSIX, while other implementations let the user pass anything, and rely
on the kernel to validate the arguments. Interestingly, even glibc does
not validate the arguments in pthread_setschedparam.
For llvm-libc, I chose not to validate the arguments either. This is
*mostly* consistent with POSIX, which says (emphasis mine):
> The supported values of policy shall *include* SCHED_FIFO, SCHED_RR,
and
> SCHED_OTHER, which are defined in the <sched.h> header.
I say mostly, because the spec does say we should return ENOTSUP if "an
attempt was made to set the attribute to an unsupported value", but I'm
not sure that's worthwhile, as it means we would need to update our list
of supported policies whenever the kernel adds a new one (and anyway, we
cannot be sure that our understanding of supported policies matches what
the running kernel actually supports).
Assisted-by: Gemini
Added:
libc/src/pthread/pthread_attr_getschedpolicy.cpp
libc/src/pthread/pthread_attr_getschedpolicy.h
libc/src/pthread/pthread_attr_setschedpolicy.cpp
libc/src/pthread/pthread_attr_setschedpolicy.h
Modified:
libc/config/linux/aarch64/entrypoints.txt
libc/config/linux/riscv/entrypoints.txt
libc/config/linux/x86_64/entrypoints.txt
libc/include/llvm-libc-types/pthread_attr_t.h
libc/include/pthread.yaml
libc/src/pthread/CMakeLists.txt
libc/src/pthread/pthread_attr_init.cpp
libc/test/src/pthread/CMakeLists.txt
libc/test/src/pthread/pthread_attr_test.cpp
Removed:
################################################################################
diff --git a/libc/config/linux/aarch64/entrypoints.txt b/libc/config/linux/aarch64/entrypoints.txt
index c0f06e70ac671..f7b2c3059df43 100644
--- a/libc/config/linux/aarch64/entrypoints.txt
+++ b/libc/config/linux/aarch64/entrypoints.txt
@@ -1119,11 +1119,13 @@ if(LLVM_LIBC_FULL_BUILD)
libc.src.pthread.pthread_attr_destroy
libc.src.pthread.pthread_attr_getdetachstate
libc.src.pthread.pthread_attr_getguardsize
+ libc.src.pthread.pthread_attr_getschedpolicy
libc.src.pthread.pthread_attr_getstack
libc.src.pthread.pthread_attr_getstacksize
libc.src.pthread.pthread_attr_init
libc.src.pthread.pthread_attr_setdetachstate
libc.src.pthread.pthread_attr_setguardsize
+ libc.src.pthread.pthread_attr_setschedpolicy
libc.src.pthread.pthread_attr_setstack
libc.src.pthread.pthread_attr_setstacksize
libc.src.pthread.pthread_condattr_destroy
diff --git a/libc/config/linux/riscv/entrypoints.txt b/libc/config/linux/riscv/entrypoints.txt
index 1eab33b2ff94f..2cabbc7031f22 100644
--- a/libc/config/linux/riscv/entrypoints.txt
+++ b/libc/config/linux/riscv/entrypoints.txt
@@ -1305,11 +1305,13 @@ if(LLVM_LIBC_FULL_BUILD)
libc.src.pthread.pthread_attr_destroy
libc.src.pthread.pthread_attr_getdetachstate
libc.src.pthread.pthread_attr_getguardsize
+ libc.src.pthread.pthread_attr_getschedpolicy
libc.src.pthread.pthread_attr_getstack
libc.src.pthread.pthread_attr_getstacksize
libc.src.pthread.pthread_attr_init
libc.src.pthread.pthread_attr_setdetachstate
libc.src.pthread.pthread_attr_setguardsize
+ libc.src.pthread.pthread_attr_setschedpolicy
libc.src.pthread.pthread_attr_setstack
libc.src.pthread.pthread_attr_setstacksize
libc.src.pthread.pthread_condattr_destroy
diff --git a/libc/config/linux/x86_64/entrypoints.txt b/libc/config/linux/x86_64/entrypoints.txt
index d9c027dfc2511..bba74cf8907f9 100644
--- a/libc/config/linux/x86_64/entrypoints.txt
+++ b/libc/config/linux/x86_64/entrypoints.txt
@@ -1316,11 +1316,13 @@ if(LLVM_LIBC_FULL_BUILD)
libc.src.pthread.pthread_attr_destroy
libc.src.pthread.pthread_attr_getdetachstate
libc.src.pthread.pthread_attr_getguardsize
+ libc.src.pthread.pthread_attr_getschedpolicy
libc.src.pthread.pthread_attr_getstack
libc.src.pthread.pthread_attr_getstacksize
libc.src.pthread.pthread_attr_init
libc.src.pthread.pthread_attr_setdetachstate
libc.src.pthread.pthread_attr_setguardsize
+ libc.src.pthread.pthread_attr_setschedpolicy
libc.src.pthread.pthread_attr_setstack
libc.src.pthread.pthread_attr_setstacksize
libc.src.pthread.pthread_condattr_destroy
diff --git a/libc/include/llvm-libc-types/pthread_attr_t.h b/libc/include/llvm-libc-types/pthread_attr_t.h
index e686ac91a6fe5..e974e2d218f03 100644
--- a/libc/include/llvm-libc-types/pthread_attr_t.h
+++ b/libc/include/llvm-libc-types/pthread_attr_t.h
@@ -13,6 +13,7 @@
typedef struct {
int __detachstate;
+ int __schedpolicy;
void *__stack;
size_t __stacksize;
size_t __guardsize;
diff --git a/libc/include/pthread.yaml b/libc/include/pthread.yaml
index 784b1c207b9f7..0059eab00f2f7 100644
--- a/libc/include/pthread.yaml
+++ b/libc/include/pthread.yaml
@@ -97,6 +97,11 @@ functions:
arguments:
- type: const pthread_attr_t *__restrict
- type: struct sched_param *__restrict
+ - name: pthread_attr_getschedpolicy
+ return_type: int
+ arguments:
+ - type: const pthread_attr_t *__restrict
+ - type: int *__restrict
- name: pthread_attr_getstack
return_type: int
arguments:
@@ -127,6 +132,11 @@ functions:
arguments:
- type: pthread_attr_t *__restrict
- type: const struct sched_param *__restrict
+ - name: pthread_attr_setschedpolicy
+ return_type: int
+ arguments:
+ - type: pthread_attr_t *
+ - type: int
- name: pthread_attr_setstack
return_type: int
arguments:
diff --git a/libc/src/pthread/CMakeLists.txt b/libc/src/pthread/CMakeLists.txt
index 846a524f436c0..06bea3bb9887f 100644
--- a/libc/src/pthread/CMakeLists.txt
+++ b/libc/src/pthread/CMakeLists.txt
@@ -6,6 +6,7 @@ add_entrypoint_object(
pthread_attr_init.h
DEPENDS
libc.include.pthread
+ libc.hdr.sched_macros
)
add_entrypoint_object(
@@ -70,6 +71,19 @@ add_entrypoint_object(
libc.include.pthread
)
+add_entrypoint_object(
+ pthread_attr_getschedpolicy
+ SRCS
+ pthread_attr_getschedpolicy.cpp
+ HDRS
+ pthread_attr_getschedpolicy.h
+ DEPENDS
+ libc.hdr.types.pthread_attr_t
+ libc.src.__support.common
+ libc.src.__support.macros.config
+ libc.src.__support.macros.null_check
+)
+
add_entrypoint_object(
pthread_attr_setschedparam
SRCS
@@ -80,6 +94,19 @@ add_entrypoint_object(
libc.include.pthread
)
+add_entrypoint_object(
+ pthread_attr_setschedpolicy
+ SRCS
+ pthread_attr_setschedpolicy.cpp
+ HDRS
+ pthread_attr_setschedpolicy.h
+ DEPENDS
+ libc.hdr.types.pthread_attr_t
+ libc.src.__support.common
+ libc.src.__support.macros.config
+ libc.src.__support.macros.null_check
+)
+
add_entrypoint_object(
pthread_attr_getstacksize
SRCS
diff --git a/libc/src/pthread/pthread_attr_getschedpolicy.cpp b/libc/src/pthread/pthread_attr_getschedpolicy.cpp
new file mode 100644
index 0000000000000..149e9b2886e03
--- /dev/null
+++ b/libc/src/pthread/pthread_attr_getschedpolicy.cpp
@@ -0,0 +1,31 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+///
+/// \file
+/// Implementation of pthread_attr_getschedpolicy.
+///
+//===----------------------------------------------------------------------===//
+
+#include "pthread_attr_getschedpolicy.h"
+#include "src/__support/common.h"
+#include "src/__support/macros/config.h"
+#include "src/__support/macros/null_check.h"
+
+namespace LIBC_NAMESPACE_DECL {
+
+LLVM_LIBC_FUNCTION(int, pthread_attr_getschedpolicy,
+ (const pthread_attr_t *__restrict attr,
+ int *__restrict policy)) {
+ LIBC_CRASH_ON_NULLPTR(attr);
+ LIBC_CRASH_ON_NULLPTR(policy);
+
+ *policy = attr->__schedpolicy;
+ return 0;
+}
+
+} // namespace LIBC_NAMESPACE_DECL
diff --git a/libc/src/pthread/pthread_attr_getschedpolicy.h b/libc/src/pthread/pthread_attr_getschedpolicy.h
new file mode 100644
index 0000000000000..8cf3c4cb57e5e
--- /dev/null
+++ b/libc/src/pthread/pthread_attr_getschedpolicy.h
@@ -0,0 +1,27 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+///
+/// \file
+/// Implementation header for pthread_attr_getschedpolicy.
+///
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_LIBC_SRC_PTHREAD_PTHREAD_ATTR_GETSCHEDPOLICY_H
+#define LLVM_LIBC_SRC_PTHREAD_PTHREAD_ATTR_GETSCHEDPOLICY_H
+
+#include "hdr/types/pthread_attr_t.h"
+#include "src/__support/macros/config.h"
+
+namespace LIBC_NAMESPACE_DECL {
+
+int pthread_attr_getschedpolicy(const pthread_attr_t *__restrict attr,
+ int *__restrict policy);
+
+} // namespace LIBC_NAMESPACE_DECL
+
+#endif // LLVM_LIBC_SRC_PTHREAD_PTHREAD_ATTR_GETSCHEDPOLICY_H
diff --git a/libc/src/pthread/pthread_attr_init.cpp b/libc/src/pthread/pthread_attr_init.cpp
index 1fc6430058f68..843dca69adc3c 100644
--- a/libc/src/pthread/pthread_attr_init.cpp
+++ b/libc/src/pthread/pthread_attr_init.cpp
@@ -8,6 +8,7 @@
#include "pthread_attr_init.h"
+#include "hdr/sched_macros.h"
#include "src/__support/common.h"
#include "src/__support/macros/config.h"
#include "src/__support/threads/thread.h" // For thread::DEFAULT_*
@@ -19,6 +20,7 @@ namespace LIBC_NAMESPACE_DECL {
LLVM_LIBC_FUNCTION(int, pthread_attr_init, (pthread_attr_t * attr)) {
*attr = pthread_attr_t{
PTHREAD_CREATE_JOINABLE, // Not detached
+ SCHED_OTHER, // Default scheduling policy
nullptr, // Let the thread manage its stack
Thread::DEFAULT_STACKSIZE, // stack size.
Thread::DEFAULT_GUARDSIZE, // Default page size for the guard size.
diff --git a/libc/src/pthread/pthread_attr_setschedpolicy.cpp b/libc/src/pthread/pthread_attr_setschedpolicy.cpp
new file mode 100644
index 0000000000000..6410339cd4c56
--- /dev/null
+++ b/libc/src/pthread/pthread_attr_setschedpolicy.cpp
@@ -0,0 +1,28 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+///
+/// \file
+/// Implementation of pthread_attr_setschedpolicy.
+///
+//===----------------------------------------------------------------------===//
+
+#include "pthread_attr_setschedpolicy.h"
+#include "src/__support/common.h"
+#include "src/__support/macros/config.h"
+#include "src/__support/macros/null_check.h"
+
+namespace LIBC_NAMESPACE_DECL {
+
+LLVM_LIBC_FUNCTION(int, pthread_attr_setschedpolicy,
+ (pthread_attr_t * attr, int policy)) {
+ LIBC_CRASH_ON_NULLPTR(attr);
+ attr->__schedpolicy = policy;
+ return 0;
+}
+
+} // namespace LIBC_NAMESPACE_DECL
diff --git a/libc/src/pthread/pthread_attr_setschedpolicy.h b/libc/src/pthread/pthread_attr_setschedpolicy.h
new file mode 100644
index 0000000000000..cc1ac5b67cd1e
--- /dev/null
+++ b/libc/src/pthread/pthread_attr_setschedpolicy.h
@@ -0,0 +1,26 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+///
+/// \file
+/// Implementation header for pthread_attr_setschedpolicy.
+///
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_LIBC_SRC_PTHREAD_PTHREAD_ATTR_SETSCHEDPOLICY_H
+#define LLVM_LIBC_SRC_PTHREAD_PTHREAD_ATTR_SETSCHEDPOLICY_H
+
+#include "hdr/types/pthread_attr_t.h"
+#include "src/__support/macros/config.h"
+
+namespace LIBC_NAMESPACE_DECL {
+
+int pthread_attr_setschedpolicy(pthread_attr_t *attr, int policy);
+
+} // namespace LIBC_NAMESPACE_DECL
+
+#endif // LLVM_LIBC_SRC_PTHREAD_PTHREAD_ATTR_SETSCHEDPOLICY_H
diff --git a/libc/test/src/pthread/CMakeLists.txt b/libc/test/src/pthread/CMakeLists.txt
index a4bbf21953653..391a634036226 100644
--- a/libc/test/src/pthread/CMakeLists.txt
+++ b/libc/test/src/pthread/CMakeLists.txt
@@ -18,7 +18,10 @@ add_libc_test(
libc.src.pthread.pthread_attr_setguardsize
libc.src.pthread.pthread_attr_setstacksize
libc.src.pthread.pthread_attr_setstack
+ libc.src.pthread.pthread_attr_getschedpolicy
+ libc.src.pthread.pthread_attr_setschedpolicy
libc.hdr.errno_macros
+ libc.hdr.sched_macros
)
add_libc_test(
diff --git a/libc/test/src/pthread/pthread_attr_test.cpp b/libc/test/src/pthread/pthread_attr_test.cpp
index bee9a1ca4f893..db1dcc0a4866c 100644
--- a/libc/test/src/pthread/pthread_attr_test.cpp
+++ b/libc/test/src/pthread/pthread_attr_test.cpp
@@ -7,14 +7,17 @@
//===----------------------------------------------------------------------===//
#include "hdr/errno_macros.h"
+#include "hdr/sched_macros.h"
#include "src/pthread/pthread_attr_destroy.h"
#include "src/pthread/pthread_attr_getdetachstate.h"
#include "src/pthread/pthread_attr_getguardsize.h"
+#include "src/pthread/pthread_attr_getschedpolicy.h"
#include "src/pthread/pthread_attr_getstack.h"
#include "src/pthread/pthread_attr_getstacksize.h"
#include "src/pthread/pthread_attr_init.h"
#include "src/pthread/pthread_attr_setdetachstate.h"
#include "src/pthread/pthread_attr_setguardsize.h"
+#include "src/pthread/pthread_attr_setschedpolicy.h"
#include "src/pthread/pthread_attr_setstack.h"
#include "src/pthread/pthread_attr_setstacksize.h"
@@ -117,3 +120,36 @@ TEST(LlvmLibcPThreadattrTest, SetAndGetStack) {
ASSERT_EQ(LIBC_NAMESPACE::pthread_attr_destroy(&attr), 0);
}
+
+TEST(LlvmLibcPThreadattrTest, SetAndGetSchedPolicy) {
+ pthread_attr_t attr;
+ ASSERT_EQ(LIBC_NAMESPACE::pthread_attr_init(&attr), 0);
+
+ int policy;
+ ASSERT_EQ(LIBC_NAMESPACE::pthread_attr_getschedpolicy(&attr, &policy), 0);
+ ASSERT_EQ(policy, SCHED_OTHER);
+
+ ASSERT_EQ(LIBC_NAMESPACE::pthread_attr_setschedpolicy(&attr, SCHED_FIFO), 0);
+ ASSERT_EQ(LIBC_NAMESPACE::pthread_attr_getschedpolicy(&attr, &policy), 0);
+ ASSERT_EQ(policy, SCHED_FIFO);
+
+ ASSERT_EQ(LIBC_NAMESPACE::pthread_attr_setschedpolicy(&attr, SCHED_RR), 0);
+ ASSERT_EQ(LIBC_NAMESPACE::pthread_attr_getschedpolicy(&attr, &policy), 0);
+ ASSERT_EQ(policy, SCHED_RR);
+
+ ASSERT_EQ(LIBC_NAMESPACE::pthread_attr_setschedpolicy(&attr, SCHED_OTHER), 0);
+ ASSERT_EQ(LIBC_NAMESPACE::pthread_attr_getschedpolicy(&attr, &policy), 0);
+ ASSERT_EQ(policy, SCHED_OTHER);
+
+ // We do not attempt to validate scheduling policies here. The OS will do that
+ // when starting a thread.
+ ASSERT_EQ(LIBC_NAMESPACE::pthread_attr_setschedpolicy(&attr, 0xBAD), 0);
+ ASSERT_EQ(LIBC_NAMESPACE::pthread_attr_getschedpolicy(&attr, &policy), 0);
+ ASSERT_EQ(policy, 0xBAD);
+
+ ASSERT_EQ(LIBC_NAMESPACE::pthread_attr_setschedpolicy(&attr, -1), 0);
+ ASSERT_EQ(LIBC_NAMESPACE::pthread_attr_getschedpolicy(&attr, &policy), 0);
+ ASSERT_EQ(policy, -1);
+
+ ASSERT_EQ(LIBC_NAMESPACE::pthread_attr_destroy(&attr), 0);
+}
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