</sect1>
</chapter>
+<chapter id="trylock-functions">
+ <title>The trylock Functions</title>
+ <para>
+ There are functions that try to acquire a lock only once and immediately
+ return a value telling about success or failure to acquire the lock.
+ They can be used if you need no access to the data protected with the lock
+ when some other thread is holding the lock. You should acquire the lock
+ later if you then need access to the data protected with the lock.
+ </para>
+
+ <para>
+ <function>spin_trylock()</function> does not spin but returns non-zero if
+ it acquires the spinlock on the first try or 0 if not. This function can
+ be used in all contexts like <function>spin_lock</function>: you must have
+ disabled the contexts that might interrupt you and acquire the spin lock.
+ </para>
+
+ <para>
+ <function>mutex_trylock()</function> does not suspend your task
+ but returns non-zero if it could lock the mutex on the first try
+ or 0 if not. This function cannot be safely used in hardware or software
+ interrupt contexts despite not sleeping.
+ </para>
+</chapter>
+
<chapter id="Examples">
<title>Common Examples</title>
<para>
};
-static DEFINE_MUTEX(cache_lock);
-+static spinlock_t cache_lock = SPIN_LOCK_UNLOCKED;
++static DEFINE_SPINLOCK(cache_lock);
static LIST_HEAD(cache);
static unsigned int cache_num = 0;
#define MAX_CACHE_SIZE 10
- int popularity;
};
- static spinlock_t cache_lock = SPIN_LOCK_UNLOCKED;
+ static DEFINE_SPINLOCK(cache_lock);
@@ -77,6 +84,7 @@
obj->id = id;
obj->popularity = 0;