[systemd-devel] [PATCH] __thread --> thread_local for C11 compat

Lennart Poettering lennart at poettering.net
Sun Dec 15 13:56:15 PST 2013


On Sun, 15.12.13 13:19, Shawn Landden (shawn at churchofgit.com) wrote:

> also make thread_local available w/o including <threads.h>

Hmm, that looks a bit too early, no? Does gcc even support this? glibc
doesn't support threads.h afaics... I couldn't find anything in
particular regarding C11 TLS support in gcc with google, any link you
can recommend? Apparently C++11 support is somewhat more existant, but
C11 support regarding threads appears to be very limited?

My glibc certainly doesn't ship thread.h. Given that gcc __thread and C11
thread_local appear to have different semantics regarding initialization
I am also a bit afraid of just defining one to the other already at this
point in time... 

> ---
>  src/libsystemd-bus/sd-bus.c     |  4 ++--
>  src/libsystemd-bus/sd-event.c   |  2 +-
>  src/libsystemd-id128/sd-id128.c |  8 ++++----
>  src/login/logind-inhibit.c      |  2 +-
>  src/shared/capability.c         |  4 ++--
>  src/shared/cgroup-util.c        |  2 +-
>  src/shared/macro.h              | 10 ++++++++++
>  src/shared/util.c               |  6 +++---
>  src/shared/virt.c               |  8 ++++----
>  9 files changed, 28 insertions(+), 18 deletions(-)
> 
> diff --git a/src/libsystemd-bus/sd-bus.c b/src/libsystemd-bus/sd-bus.c
> index 4eaceef..64cd663 100644
> --- a/src/libsystemd-bus/sd-bus.c
> +++ b/src/libsystemd-bus/sd-bus.c
> @@ -2815,13 +2815,13 @@ static int bus_default(int (*bus_open)(sd_bus **), sd_bus **default_bus, sd_bus
>  }
>  
>  _public_ int sd_bus_default_system(sd_bus **ret) {
> -        static __thread sd_bus *default_system_bus = NULL;
> +        static thread_local sd_bus *default_system_bus = NULL;
>  
>          return bus_default(sd_bus_open_system, &default_system_bus, ret);
>  }
>  
>  _public_ int sd_bus_default_user(sd_bus **ret) {
> -        static __thread sd_bus *default_user_bus = NULL;
> +        static thread_local sd_bus *default_user_bus = NULL;
>  
>          return bus_default(sd_bus_open_user, &default_user_bus, ret);
>  }
> diff --git a/src/libsystemd-bus/sd-event.c b/src/libsystemd-bus/sd-event.c
> index 06c84d7..727528b 100644
> --- a/src/libsystemd-bus/sd-event.c
> +++ b/src/libsystemd-bus/sd-event.c
> @@ -2116,7 +2116,7 @@ _public_ int sd_event_get_now_monotonic(sd_event *e, uint64_t *usec) {
>  
>  _public_ int sd_event_default(sd_event **ret) {
>  
> -        static __thread sd_event *default_event = NULL;
> +        static thread_local sd_event *default_event = NULL;
>          sd_event *e;
>          int r;
>  
> diff --git a/src/libsystemd-id128/sd-id128.c b/src/libsystemd-id128/sd-id128.c
> index 07d2415..9ee40ab 100644
> --- a/src/libsystemd-id128/sd-id128.c
> +++ b/src/libsystemd-id128/sd-id128.c
> @@ -104,8 +104,8 @@ static sd_id128_t make_v4_uuid(sd_id128_t id) {
>  }
>  
>  _public_ int sd_id128_get_machine(sd_id128_t *ret) {
> -        static __thread sd_id128_t saved_machine_id;
> -        static __thread bool saved_machine_id_valid = false;
> +        static thread_local sd_id128_t saved_machine_id;
> +        static thread_local bool saved_machine_id_valid = false;
>          _cleanup_close_ int fd = -1;
>          char buf[33];
>          ssize_t k;
> @@ -153,8 +153,8 @@ _public_ int sd_id128_get_machine(sd_id128_t *ret) {
>  }
>  
>  _public_ int sd_id128_get_boot(sd_id128_t *ret) {
> -        static __thread sd_id128_t saved_boot_id;
> -        static __thread bool saved_boot_id_valid = false;
> +        static thread_local sd_id128_t saved_boot_id;
> +        static thread_local bool saved_boot_id_valid = false;
>          _cleanup_close_ int fd = -1;
>          char buf[36];
>          ssize_t k;
> diff --git a/src/login/logind-inhibit.c b/src/login/logind-inhibit.c
> index ec6a722..042586d 100644
> --- a/src/login/logind-inhibit.c
> +++ b/src/login/logind-inhibit.c
> @@ -413,7 +413,7 @@ bool manager_is_inhibited(
>  }
>  
>  const char *inhibit_what_to_string(InhibitWhat w) {
> -        static __thread char buffer[97];
> +        static thread_local char buffer[97];
>          char *p;
>  
>          if (w < 0 || w >= _INHIBIT_WHAT_MAX)
> diff --git a/src/shared/capability.c b/src/shared/capability.c
> index 3219520..f34f6ba 100644
> --- a/src/shared/capability.c
> +++ b/src/shared/capability.c
> @@ -55,8 +55,8 @@ int have_effective_cap(int value) {
>  }
>  
>  unsigned long cap_last_cap(void) {
> -        static __thread unsigned long saved;
> -        static __thread bool valid = false;
> +        static thread_local unsigned long saved;
> +        static thread_local bool valid = false;
>          unsigned long p;
>  
>          if (valid)
> diff --git a/src/shared/cgroup-util.c b/src/shared/cgroup-util.c
> index 2c2ffc5..309f65d 100644
> --- a/src/shared/cgroup-util.c
> +++ b/src/shared/cgroup-util.c
> @@ -480,7 +480,7 @@ static int join_path(const char *controller, const char *path, const char *suffi
>  
>  int cg_get_path(const char *controller, const char *path, const char *suffix, char **fs) {
>          const char *p;
> -        static __thread bool good = false;
> +        static thread_local bool good = false;
>  
>          assert(fs);
>  
> diff --git a/src/shared/macro.h b/src/shared/macro.h
> index fd3762e..c0597fa 100644
> --- a/src/shared/macro.h
> +++ b/src/shared/macro.h
> @@ -27,6 +27,16 @@
>  #include <sys/uio.h>
>  #include <inttypes.h>
>  
> +#if __STDC_VERSION__ >= 201112L && !defined(__STDC_NO_THREADS__)
> +#else
> +#  define _Thread_local __thread
> +#endif
> +
> +/* make thread_local available w/o including <threads.h> */
> +#ifndef thread_local
> +# define thread_local _Thread_local
> +#endif
> +
>  #define _printf_(a,b) __attribute__ ((format (printf, a, b)))
>  #define _alloc_(...) __attribute__ ((alloc_size(__VA_ARGS__)))
>  #define _sentinel_ __attribute__ ((sentinel))
> diff --git a/src/shared/util.c b/src/shared/util.c
> index 7c73074..0ce6f70 100644
> --- a/src/shared/util.c
> +++ b/src/shared/util.c
> @@ -86,7 +86,7 @@ static volatile unsigned cached_columns = 0;
>  static volatile unsigned cached_lines = 0;
>  
>  size_t page_size(void) {
> -        static __thread size_t pgsz = 0;
> +        static thread_local size_t pgsz = 0;
>          long r;
>  
>          if (_likely_(pgsz > 0))
> @@ -4580,7 +4580,7 @@ char *strjoin(const char *x, ...) {
>  }
>  
>  bool is_main_thread(void) {
> -        static __thread int cached = 0;
> +        static thread_local int cached = 0;
>  
>          if (_unlikely_(cached == 0))
>                  cached = getpid() == gettid() ? 1 : -1;
> @@ -4798,7 +4798,7 @@ static const char *const __signal_table[] = {
>  DEFINE_PRIVATE_STRING_TABLE_LOOKUP(__signal, int);
>  
>  const char *signal_to_string(int signo) {
> -        static __thread char buf[sizeof("RTMIN+")-1 + DECIMAL_STR_MAX(int) + 1];
> +        static thread_local char buf[sizeof("RTMIN+")-1 + DECIMAL_STR_MAX(int) + 1];
>          const char *name;
>  
>          name = __signal_to_string(signo);
> diff --git a/src/shared/virt.c b/src/shared/virt.c
> index 4e18638..c79d35d 100644
> --- a/src/shared/virt.c
> +++ b/src/shared/virt.c
> @@ -150,8 +150,8 @@ static int detect_vm_dmi(const char **_id) {
>  /* Returns a short identifier for the various VM implementations */
>  int detect_vm(const char **id) {
>          _cleanup_free_ char *hvtype = NULL, *cpuinfo_contents = NULL;
> -        static __thread int cached_found = -1;
> -        static __thread const char *cached_id = NULL;
> +        static thread_local int cached_found = -1;
> +        static thread_local const char *cached_id = NULL;
>          const char *_id = NULL;
>          int r;
>  
> @@ -215,8 +215,8 @@ finish:
>  
>  int detect_container(const char **id) {
>  
> -        static __thread int cached_found = -1;
> -        static __thread const char *cached_id = NULL;
> +        static thread_local int cached_found = -1;
> +        static thread_local const char *cached_id = NULL;
>  
>          _cleanup_free_ char *e = NULL;
>          const char *_id = NULL;


Lennart

-- 
Lennart Poettering, Red Hat


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