[cadcdev-svn-commits] SF.net SVN: cadcdev: [588] kos

[<ljs...@us...>]

Revision: 588
          http://cadcdev.svn.sourceforge.net/cadcdev/?rev=588&view=rev
Author:   ljsebald
Date:     2008-05-19 20:05:38 -0700 (Mon, 19 May 2008)

Log Message:
-----------
Add support for "upgrading" a reader/writer semaphore from a read lock to a write lock.

Modified Paths:
--------------
    kos/include/kos/rwsem.h
    kos/kernel/thread/rwsem.c

Modified: kos/include/kos/rwsem.h
===================================================================
--- kos/include/kos/rwsem.h	2008-05-20 02:45:34 UTC (rev 587)
+++ kos/include/kos/rwsem.h	2008-05-20 03:05:38 UTC (rev 588)
@@ -71,6 +71,17 @@
     EWOULDBLOCK - would block */
 int rwsem_write_trylock(rw_semaphore_t *s);
 
+/* "Upgrade" a read lock to a write lock. Returns -1 on error.
+    EPERM - called inside an interrupt
+    EINTR - was interrupted */
+int rwsem_read_upgrade(rw_semaphore_t *s);
+
+/* Attempt to upgrade a read lock to a write lock. If the call to
+   rwsem_read_upgrade() would normally block, return -1 for error.
+   Note that on error, the read lock is still held.
+    EWOULDBLOCK - would block */
+int rwsem_read_tryupgrade(rw_semaphore_t *s);
+
 /* Return the reader/writer semaphore reader count */
 int rwsem_read_count(rw_semaphore_t *s);
 

Modified: kos/kernel/thread/rwsem.c
===================================================================
--- kos/kernel/thread/rwsem.c	2008-05-20 02:45:34 UTC (rev 587)
+++ kos/kernel/thread/rwsem.c	2008-05-20 03:05:38 UTC (rev 588)
@@ -201,6 +201,60 @@
     return rv;
 }
 
+/* "Upgrade" a read lock to a write lock. */
+int rwsem_read_upgrade(rw_semaphore_t *s) {
+    int old, rv = 0;
+
+    if(irq_inside_int()) {
+        dbglog(DBG_WARNING, "rwsem_read_upgrade: called inside interrupt\n");
+        errno = EPERM;
+        return -1;
+    }
+
+    old = irq_disable();
+
+    --s->read_count;
+
+    /* If there are still other readers, wait patiently for our turn. */
+    if(s->read_count) {
+        rv = genwait_wait(&s->write_lock, "rwsem_read_upgrade", 0, NULL);
+
+        if(rv < 0) {
+            assert(errno == EINTR);
+            rv = -1;
+        }
+        else {
+            s->write_lock = 1;
+        }
+    }
+    else {
+        s->write_lock = 1;
+    }
+
+    irq_restore(old);
+    return rv;
+}
+
+/* Attempt to upgrade a read lock to a write lock, but do not block. */
+int rwsem_read_tryupgrade(rw_semaphore_t *s) {
+    int old, rv;
+
+    old = irq_disable();
+
+    if(s->read_count != 1) {
+        rv = -1;
+        errno = EWOULDBLOCK;
+    }
+    else {
+        rv = 0;
+        s->read_count = 0;
+        s->write_lock = 1;
+    }
+
+    irq_restore(old);
+    return rv;
+}
+
 /* Return the current reader count */
 int rwsem_read_count(rw_semaphore_t *s) {
     return s->read_count;


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