optimize out setting up robust list with kernel when not needed

as a result of commit 12e1e324683a1d381b7f15dd36c99b37dd44d940, kernel
processing of the robust list is only needed for process-shared
mutexes. previously the first attempt to lock any owner-tracked mutex
resulted in robust list initialization and a set_robust_list syscall.
this is no longer necessary, and since the kernel's record of the
robust list must now be cleared at thread exit time for detached
threads, optimizing it out is more worthwhile than before too.

diff --git a/src/env/__init_tls.c b/src/env/__init_tls.c
index e651c7a..ac4d9e7 100644 (file)
--- a/src/env/__init_tls.c
+++ b/src/env/__init_tls.c
@@ -18,6 +18,7 @@ int __init_tp(void *p)
        libc.has_thread_pointer = 1;
        td->tid = __syscall(SYS_set_tid_address, &td->tid);
        td->locale = &libc.global_locale;
+       td->robust_list.head = &td->robust_list.head;
        return 0;
 }
 

diff --git a/src/process/fork.c b/src/process/fork.c
index 43c52bc..8d67682 100644 (file)
--- a/src/process/fork.c
+++ b/src/process/fork.c
@@ -25,7 +25,8 @@ pid_t fork(void)
        if (libc.has_thread_pointer && !ret) {
                pthread_t self = __pthread_self();
                self->tid = __syscall(SYS_gettid);
-               memset(&self->robust_list, 0, sizeof self->robust_list);
+               self->robust_list.off = 0;
+               self->robust_list.pending = 0;
                libc.threads_minus_1 = 0;
        }
        __restore_sigs(&set);

diff --git a/src/thread/pthread_create.c b/src/thread/pthread_create.c
index 893773f..8b0135b 100644 (file)
--- a/src/thread/pthread_create.c
+++ b/src/thread/pthread_create.c
@@ -268,6 +268,7 @@ int __pthread_create(pthread_t *restrict res, const pthread_attr_t *restrict att
                do_sched = new->startlock[0] = 1;
                __block_app_sigs(new->sigmask);
        }
+       new->robust_list.head = &new->robust_list.head;
        new->unblock_cancel = self->cancel;
        new->canary = self->canary;
 

diff --git a/src/thread/pthread_mutex_trylock.c b/src/thread/pthread_mutex_trylock.c
index cb93565..0df3ce2 100644 (file)
--- a/src/thread/pthread_mutex_trylock.c
+++ b/src/thread/pthread_mutex_trylock.c
@@ -7,12 +7,6 @@ int __pthread_mutex_trylock_owner(pthread_mutex_t *m)
        pthread_t self = __pthread_self();
        int tid = self->tid;
 
-       if (!self->robust_list.off) {
-               __syscall(SYS_set_robust_list, &self->robust_list, 3*sizeof(long));
-               self->robust_list.head = &self->robust_list.head;
-               self->robust_list.off = (char*)&m->_m_lock-(char *)&m->_m_next;
-       }
-
        old = m->_m_lock;
        own = old & 0x7fffffff;
        if (own == tid && (type&3) == PTHREAD_MUTEX_RECURSIVE) {
@@ -23,6 +17,10 @@ int __pthread_mutex_trylock_owner(pthread_mutex_t *m)
        if (own == 0x40000000) return ENOTRECOVERABLE;
 
        if (m->_m_type & 128) {
+               if (!self->robust_list.off) {
+                       self->robust_list.off = (char*)&m->_m_lock-(char *)&m->_m_next;
+                       __syscall(SYS_set_robust_list, &self->robust_list, 3*sizeof(long));
+               }
                if (m->_m_waiters) tid |= 0x80000000;
                self->robust_list.pending = &m->_m_next;
        }