diff options
Diffstat (limited to 'sysdeps/nptl/bits/thread-shared-types.h')
| -rw-r--r-- | sysdeps/nptl/bits/thread-shared-types.h | 22 |
1 files changed, 21 insertions, 1 deletions
diff --git a/sysdeps/nptl/bits/thread-shared-types.h b/sysdeps/nptl/bits/thread-shared-types.h index 1e2092a05d..05c94e7a71 100644 --- a/sysdeps/nptl/bits/thread-shared-types.h +++ b/sysdeps/nptl/bits/thread-shared-types.h @@ -124,7 +124,27 @@ struct __pthread_mutex_s unsigned int __nusers; #endif /* KIND must stay at this position in the structure to maintain - binary compatibility with static initializers. */ + binary compatibility with static initializers. + + Concurrency notes: + The __kind of a mutex is initialized either by the static + PTHREAD_MUTEX_INITIALIZER or by a call to pthread_mutex_init. + + After a mutex has been initialized, the __kind of a mutex is usually not + changed. BUT it can be set to -1 in pthread_mutex_destroy or elision can + be enabled. This is done concurrently in the pthread_mutex_*lock functions + by using the macro FORCE_ELISION. This macro is only defined for + architectures which supports lock elision. + + For elision, there are the flags PTHREAD_MUTEX_ELISION_NP and + PTHREAD_MUTEX_NO_ELISION_NP which can be set in addition to the already set + type of a mutex. + Before a mutex is initialized, only PTHREAD_MUTEX_NO_ELISION_NP can be set + with pthread_mutexattr_settype. + After a mutex has been initialized, the functions pthread_mutex_*lock can + enable elision - if the mutex-type and the machine supports it - by setting + the flag PTHREAD_MUTEX_ELISION_NP. This is done concurrently. Afterwards + the lock / unlock functions are using specific elision code-paths. */ int __kind; __PTHREAD_COMPAT_PADDING_MID #if __PTHREAD_MUTEX_NUSERS_AFTER_KIND |