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41 .Nm spin_unlock_quick ,
49 .Fn spin_init "struct spinlock *mtx"
51 .Fn spin_uninit "struct spinlock *mtx"
53 .Fn spin_lock "struct spinlock *mtx"
55 .Fn spin_lock_quick "globaldata_t gd" "struct spinlock *mtx"
57 .Fn spin_trylock "struct spinlock *mtx"
59 .Fn spin_unlock "struct spinlock *mtx"
61 .Fn spin_unlock_quick "globaldata_t gd" "struct spinlock *mtx"
65 structure and call API are defined in the
69 header files, respectively.
73 function initializes a new
76 The structure is cleaned up with
78 when it is no longer needed.
82 function obtains an exclusive
85 A thread may hold any number of exclusive spinlocks but should always
86 be mindful of ordering deadlocks.
91 if the spinlock was successfully obtained and
94 If you have the current CPU's
96 pointer in hand you can call
98 but most code will just call the normal version.
99 A spinlock used only for exclusive access has about the same overhead
100 as a mutex based on a locked bus cycle.
102 A previously obtained exclusive spinlock is released by calling either
105 .Fn spin_unlock_quick .
109 function locks a pool spinlock associated with a given address.
110 The spinlock's lifetime is not tied to any objects at the address.
111 The function returns the locked spinlock.
114 function unlocks a pool spinlock associated with an address.
115 Pool spinlocks need not be initialized.
116 .Sh IMPLEMENTATION NOTES
117 A thread may not hold any spinlock across a blocking condition or
119 LWKT tokens should be used for situations where you want an exclusive
120 run-time lock that will survive a blocking condition or thread switch.
121 Tokens will be automatically unlocked when a thread switches away and
122 relocked when the thread is switched back in.
123 If you want a lock that survives a blocking condition or thread switch
124 without being released, use
126 locks or LWKT reader/writer locks.
129 core spinlocks should only be used around small contained sections of
131 For example, to manage a reference count or to implement higher level
133 Both the token code and the
135 code use exclusive spinlocks internally.
136 Core spinlocks should not be used around large chunks of code.
138 Holding one or more spinlocks will disable thread preemption by
139 another thread (e.g. preemption by an interrupt thread),
140 and will prevent FAST interrupts or IPIs from running.
141 This means that a FAST interrupt, IPI and any threaded interrupt
142 (which is basically all interrupts except the clock interrupt)
143 will still be scheduled for later execution,
144 but will not be able to preempt the current thread.
146 A thread may hold any number of exclusive
151 A thread will not block, switch away, or lose its critical section
152 while obtaining or releasing a spinlock.
153 Spinlocks do not use IPIs or other mechanisms.
154 They are considered to be a very low level mechanism.
156 If a spinlock can not be obtained after one second a warning will be
157 printed on the console.
158 If a system panic occurs, spinlocks will succeed after one second in
159 order to allow the panic operation to proceed.
161 If you have a complex structure such as a
163 which contains a token or
165 lock, it is legal to directly access the internal spinlock embedded
166 in those structures for other purposes as long as the spinlock is not
167 held when you issue the token or
171 The uncontended path of the spinlock implementation is in
172 .Pa /sys/sys/spinlock2.h .
173 The core of the spinlock implementation is in
174 .Pa /sys/kern/kern_spinlock.c .
183 implementation first appeared in
189 implementation was written by
191 and was later extended by
193 This manual page was written by