Changeset 235d31d in mainline for uspace/lib/c/generic/futex.c

Timestamp:

2014-12-22T17:47:40Z (9 years ago)

Author:

Jakub Jermar <jakub@…>

Branches:

lfn, master, serial, ticket/834-toolchain-update, topic/msim-upgrade, topic/simplify-dev-export

Children:

8c7d5ad

Parents:

eae91e0 (diff), 759ea0d (diff)
Note: this is a merge changeset, the changes displayed below correspond to the merge itself.
Use the (diff) links above to see all the changes relative to each parent.

Message:

Merge the CHT pre-integration branch

This branch contains:

• the merge of lp:~adam-hraska+lp/helenos/rcu, which brings:

• a new preemptible kernel RCU variant called A-RCU,
• a preemptible variant of Podzimek's non-preemptible kernel RCU and
• a new variant of usersace RCU,
• a new concurrent hash table (CHT) implementation based on RCU,
• a deployment of CHT in kernel futex handling,
• a deployment of the userspace RCU in the implementation of upgradable futexes,

all described in Adam Hraska's master thesis named Read-Copy-Update
for HelenOS, defended in 2013 at MFF UK; furthemore, the branch
fixes two synchronization bugs in condvars and waitq, respectively:

• revid:adam.hraska+hos@gmail.com-20121116144921-3to9u1tn1sg07rg7
• revid:adam.hraska+hos@gmail.com-20121116173623-km7gwtqixwudpe66

• build fixes required to pass make check
• overhaul of ia64 and sparc64 trap handling, to allow exc_dispatch() to be used now when the kernel is more picky about CPU state accounting
• an important fix of the sparc64/sun4v preemptible trap handler
• various other fixes of issues discovered on non-x86 architectures

File:

• uspace/lib/c/generic/futex.c (modified) (2 diffs)

uspace/lib/c/generic/futex.c

@@ -35 +35 @@
 #include <futex.h>
 #include <atomic.h>
-#include <libarch/barrier.h>
-#include <libc.h>
-#include <sys/types.h>
 
 /** Initialize futex counter.
@@ -47 +44 @@
 void futex_initialize(futex_t *futex, int val)
 {
-        atomic_set(futex, val);
+        atomic_set(&futex->val, val);
 }
 
-/** Try to down the futex.
- *
- * @param futex Futex.
- *
- * @return Non-zero if the futex was acquired.
- * @return Zero if the futex was not acquired.
- *
- */
-int futex_trydown(futex_t *futex)
+
+#ifdef FUTEX_UPGRADABLE
+
+int _upgrade_futexes = 0;
+static futex_t upg_and_wait_futex = FUTEX_INITIALIZER;
+
+void futex_upgrade_all_and_wait(void)
 {
-        int rc;
-
-        rc = cas(futex, 1, 0);
-        CS_ENTER_BARRIER();
-
-        return rc;
+        futex_down(&upg_and_wait_futex);
+        
+        if (!_upgrade_futexes) {
+                rcu_assign(_upgrade_futexes, 1);
+                _rcu_synchronize(BM_BLOCK_THREAD);
+        }
+        
+        futex_up(&upg_and_wait_futex);
 }
 
-/** Down the futex.
- *
- * @param futex Futex.
- *
- * @return ENOENT if there is no such virtual address.
- * @return Zero in the uncontended case.
- * @return Otherwise one of ESYNCH_OK_ATOMIC or ESYNCH_OK_BLOCKED.
- *
- */
-int futex_down(futex_t *futex)
-{
-        atomic_signed_t nv;
-
-        nv = (atomic_signed_t) atomic_predec(futex);
-        CS_ENTER_BARRIER();
-        if (nv < 0)
-                return __SYSCALL1(SYS_FUTEX_SLEEP, (sysarg_t) &futex->count);
-        
-        return 0;
-}
-
-/** Up the futex.
- *
- * @param futex Futex.
- *
- * @return ENOENT if there is no such virtual address.
- * @return Zero in the uncontended case.
- *
- */
-int futex_up(futex_t *futex)
-{
-        CS_LEAVE_BARRIER();
-
-        if ((atomic_signed_t) atomic_postinc(futex) < 0)
-                return __SYSCALL1(SYS_FUTEX_WAKEUP, (sysarg_t) &futex->count);
-        
-        return 0;
-}
+#endif
 
 /** @}