forked from mozilla/gecko-dev
-
Notifications
You must be signed in to change notification settings - Fork 2
/
DeadlockDetector.h
588 lines (532 loc) · 19.7 KB
/
DeadlockDetector.h
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*-
* vim: sw=4 ts=4 et :
* ***** BEGIN LICENSE BLOCK *****
* Version: MPL 1.1/GPL 2.0/LGPL 2.1
*
* The contents of this file are subject to the Mozilla Public License Version
* 1.1 (the "License"); you may not use this file except in compliance with
* the License. You may obtain a copy of the License at
* http://www.mozilla.org/MPL/
*
* Software distributed under the License is distributed on an "AS IS" basis,
* WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License
* for the specific language governing rights and limitations under the
* License.
*
* The Original Code is mozilla.org code.
*
* The Initial Developer of the Original Code is
* Netscape Communications Corporation.
* Portions created by the Initial Developer are Copyright (C) 1998
* the Initial Developer. All Rights Reserved.
*
* Contributor(s):
* Chris Jones <jones.chris.g@gmail.com>
*
* Alternatively, the contents of this file may be used under the terms of
* either of the GNU General Public License Version 2 or later (the "GPL"),
* or the GNU Lesser General Public License Version 2.1 or later (the "LGPL"),
* in which case the provisions of the GPL or the LGPL are applicable instead
* of those above. If you wish to allow use of your version of this file only
* under the terms of either the GPL or the LGPL, and not to allow others to
* use your version of this file under the terms of the MPL, indicate your
* decision by deleting the provisions above and replace them with the notice
* and other provisions required by the GPL or the LGPL. If you do not delete
* the provisions above, a recipient may use your version of this file under
* the terms of any one of the MPL, the GPL or the LGPL.
*
* ***** END LICENSE BLOCK ***** */
#ifndef mozilla_DeadlockDetector_h
#define mozilla_DeadlockDetector_h
#include <stdlib.h>
#include "plhash.h"
#include "prlock.h"
#include "nsTArray.h"
#ifdef NS_TRACE_MALLOC
# include "nsTraceMalloc.h"
#endif // ifdef NS_TRACE_MALLOC
namespace mozilla {
// FIXME bug 456272: split this off into a convenience API on top of
// nsStackWalk?
class NS_COM_GLUE CallStack
{
private:
#ifdef NS_TRACE_MALLOC
typedef nsTMStackTraceID callstack_id;
// needs to be a macro to avoid disturbing the backtrace
# define NS_GET_BACKTRACE() NS_TraceMallocGetStackTrace()
#else
typedef void* callstack_id;
# define NS_GET_BACKTRACE() 0
#endif // ifdef NS_TRACE_MALLOC
callstack_id mCallStack;
public:
/**
* CallStack
* *ALWAYS* *ALWAYS* *ALWAYS* call this with no arguments. This
* constructor takes an argument *ONLY* so that |GET_BACKTRACE()|
* can be evaluated in the stack frame of the caller, rather than
* that of the constructor.
*
* *BEWARE*: this means that calling this constructor with no
* arguments is not the same as a "default, do-nothing"
* constructor: it *will* construct a backtrace. This can cause
* unexpected performance issues.
*/
CallStack(const callstack_id aCallStack = NS_GET_BACKTRACE()) :
mCallStack(aCallStack)
{
}
CallStack(const CallStack& aFrom) :
mCallStack(aFrom.mCallStack)
{
}
CallStack& operator=(const CallStack& aFrom)
{
mCallStack = aFrom.mCallStack;
return *this;
}
bool operator==(const CallStack& aOther) const
{
return mCallStack == aOther.mCallStack;
}
bool operator!=(const CallStack& aOther) const
{
return mCallStack != aOther.mCallStack;
}
// FIXME bug 456272: if this is split off,
// NS_TraceMallocPrintStackTrace should be modified to print into
// an nsACString
void Print(FILE* f) const
{
#ifdef NS_TRACE_MALLOC
if (this != &kNone && mCallStack) {
NS_TraceMallocPrintStackTrace(f, mCallStack);
return;
}
#endif
fputs(" [stack trace unavailable]\n", f);
}
/** The "null" callstack. */
static const CallStack kNone;
};
/**
* DeadlockDetector
*
* The following is an approximate description of how the deadlock detector
* works.
*
* The deadlock detector ensures that all blocking resources are
* acquired according to a partial order P. One type of blocking
* resource is a lock. If a lock l1 is acquired (locked) before l2,
* then we say that |l1 <_P l2|. The detector flags an error if two
* locks l1 and l2 have an inconsistent ordering in P; that is, if
* both |l1 <_P l2| and |l2 <_P l1|. This is a potential error
* because a thread acquiring l1,l2 according to the first order might
* race with a thread acquiring them according to the second order.
* If this happens under the right conditions, then the acquisitions
* will deadlock.
*
* This deadlock detector doesn't know at compile-time what P is. So,
* it tries to discover the order at run time. More precisely, it
* finds <i>some</i> order P, then tries to find chains of resource
* acquisitions that violate P. An example acquisition sequence, and
* the orders they impose, is
* l1.lock() // current chain: [ l1 ]
* // order: { }
*
* l2.lock() // current chain: [ l1, l2 ]
* // order: { l1 <_P l2 }
*
* l3.lock() // current chain: [ l1, l2, l3 ]
* // order: { l1 <_P l2, l2 <_P l3, l1 <_P l3 }
* // (note: <_P is transitive, so also |l1 <_P l3|)
*
* l2.unlock() // current chain: [ l1, l3 ]
* // order: { l1 <_P l2, l2 <_P l3, l1 <_P l3 }
* // (note: it's OK, but weird, that l2 was unlocked out
* // of order. we still have l1 <_P l3).
*
* l2.lock() // current chain: [ l1, l3, l2 ]
* // order: { l1 <_P l2, l2 <_P l3, l1 <_P l3,
* l3 <_P l2 (!!!) }
* BEEP BEEP! Here the detector will flag a potential error, since
* l2 and l3 were used inconsistently (and potentially in ways that
* would deadlock).
*/
template <typename T>
class DeadlockDetector
{
public:
/**
* ResourceAcquisition
* Consists simply of a resource and the calling context from
* which it was acquired. We pack this information together so
* that it can be returned back to the caller when a potential
* deadlock has been found.
*/
struct ResourceAcquisition
{
const T* mResource;
CallStack mCallContext;
ResourceAcquisition(
const T* aResource,
const CallStack aCallContext=CallStack::kNone) :
mResource(aResource),
mCallContext(aCallContext)
{
}
ResourceAcquisition(const ResourceAcquisition& aFrom) :
mResource(aFrom.mResource),
mCallContext(aFrom.mCallContext)
{
}
ResourceAcquisition& operator=(const ResourceAcquisition& aFrom)
{
mResource = aFrom.mResource;
mCallContext = aFrom.mCallContext;
return *this;
}
};
typedef nsTArray<ResourceAcquisition> ResourceAcquisitionArray;
private:
typedef nsTArray<PLHashEntry*> HashEntryArray;
typedef typename HashEntryArray::index_type index_type;
typedef typename HashEntryArray::size_type size_type;
enum {
NoIndex = HashEntryArray::NoIndex
};
/**
* Value type for the ordering table. Contains the other
* resources on which an ordering constraint |key < other|
* exists. The catch is that we also store the calling context at
* which the other resource was acquired; this improves the
* quality of error messages when potential deadlock is detected.
*/
struct OrderingEntry
{
OrderingEntry() :
mFirstSeen(CallStack::kNone),
mOrderedLT() // FIXME bug 456272: set to empirical
{ // dep size?
}
~OrderingEntry()
{
}
CallStack mFirstSeen; // first site from which the resource appeared
HashEntryArray mOrderedLT; // this <_o Other
};
static void* TableAlloc(void* /*pool*/, PRSize size)
{
return operator new(size);
}
static void TableFree(void* /*pool*/, void* item)
{
operator delete(item);
}
static PLHashEntry* EntryAlloc(void* /*pool*/, const void* key)
{
return new PLHashEntry;
}
static void EntryFree(void* /*pool*/, PLHashEntry* entry, PRUintn flag)
{
delete static_cast<T*>(const_cast<void*>(entry->key));
delete static_cast<OrderingEntry*>(entry->value);
entry->value = 0;
if (HT_FREE_ENTRY == flag)
delete entry;
}
static PLHashNumber HashKey(const void* aKey)
{
return NS_PTR_TO_INT32(aKey) >> 2;
}
static const PLHashAllocOps kAllocOps;
// Hash table "interface" the rest of the code should use
PLHashEntry** GetEntry(const T* aKey)
{
return PL_HashTableRawLookup(mOrdering, HashKey(aKey), aKey);
}
void PutEntry(T* aKey)
{
PL_HashTableAdd(mOrdering, aKey, new OrderingEntry());
}
// XXX need these helper methods because OrderingEntry doesn't have
// XXX access to underlying PLHashEntry
/**
* Add the order |aFirst <_o aSecond|.
*
* WARNING: this does not check whether it's sane to add this
* order. In the "best" bad case, when this order already exists,
* adding it anyway may unnecessarily result in O(n^2) space. In
* the "worst" bad case, adding it anyway will cause
* |InTransitiveClosure()| to diverge.
*/
void AddOrder(PLHashEntry* aLT, PLHashEntry* aGT)
{
static_cast<OrderingEntry*>(aLT->value)->mOrderedLT
.InsertElementSorted(aGT);
}
/**
* Return true iff the order |aFirst < aSecond| has been
* *explicitly* added.
*
* Does not consider transitivity.
*/
bool IsOrdered(const PLHashEntry* aFirst, const PLHashEntry* aSecond)
const
{
return NoIndex !=
static_cast<const OrderingEntry*>(aFirst->value)->mOrderedLT
.BinaryIndexOf(aSecond);
}
/**
* Return a pointer to the array of all elements "that" for
* which the order |this < that| has been explicitly added.
*
* NOTE: this does *not* consider transitive orderings.
*/
PLHashEntry* const* GetOrders(const PLHashEntry* aEntry) const
{
return static_cast<const OrderingEntry*>(aEntry->value)->mOrderedLT
.Elements();
}
/**
* Return the number of elements "that" for which the order
* |this < that| has been explicitly added.
*
* NOTE: this does *not* consider transitive orderings.
*/
size_type NumOrders(const PLHashEntry* aEntry) const
{
return static_cast<const OrderingEntry*>(aEntry->value)->mOrderedLT
.Length();
}
/** Make a ResourceAcquisition out of |aEntry|. */
ResourceAcquisition MakeResourceAcquisition(const PLHashEntry* aEntry)
const
{
return ResourceAcquisition(
static_cast<const T*>(aEntry->key),
static_cast<const OrderingEntry*>(aEntry->value)->mFirstSeen);
}
// Throwaway RAII lock to make the following code safer.
struct PRAutoLock
{
PRAutoLock(PRLock* aLock) : mLock(aLock) { PR_Lock(mLock); }
~PRAutoLock() { PR_Unlock(mLock); }
PRLock* mLock;
};
public:
static const PRUint32 kDefaultNumBuckets;
/**
* DeadlockDetector
* Create a new deadlock detector.
*
* @param aNumResourcesGuess Guess at approximate number of resources
* that will be checked.
*/
DeadlockDetector(PRUint32 aNumResourcesGuess = kDefaultNumBuckets)
{
mOrdering = PL_NewHashTable(aNumResourcesGuess,
HashKey,
PL_CompareValues, PL_CompareValues,
&kAllocOps, 0);
if (!mOrdering)
NS_RUNTIMEABORT("couldn't initialize resource ordering table");
mLock = PR_NewLock();
if (!mLock)
NS_RUNTIMEABORT("couldn't allocate deadlock detector lock");
}
/**
* ~DeadlockDetector
*
* *NOT* thread safe.
*/
~DeadlockDetector()
{
PL_HashTableDestroy(mOrdering);
PR_DestroyLock(mLock);
}
/**
* Add
* Make the deadlock detector aware of |aResource|.
*
* WARNING: The deadlock detector owns |aResource|.
*
* Thread safe.
*
* @param aResource Resource to make deadlock detector aware of.
*/
void Add(T* aResource)
{
PRAutoLock _(mLock);
PutEntry(aResource);
}
// Nb: implementing a Remove() method makes the detector "more
// unsound." By removing a resource from the orderings, deadlocks
// may be missed that would otherwise have been found. However,
// removing resources possibly reduces the # of false positives,
// and additionally saves space. So it's a trade off; we have
// chosen to err on the side of caution and not implement Remove().
/**
* CheckAcquisition This method is called after acquiring |aLast|,
* but before trying to acquire |aProposed| from |aCallContext|.
* It determines whether actually trying to acquire |aProposed|
* will create problems. It is OK if |aLast| is NULL; this is
* interpreted as |aProposed| being the thread's first acquisition
* of its current chain.
*
* Iff acquiring |aProposed| may lead to deadlock for some thread
* interleaving (including the current one!), the cyclical
* dependency from which this was deduced is returned. Otherwise,
* 0 is returned.
*
* If a potential deadlock is detected and a resource cycle is
* returned, it is the *caller's* responsibility to free it.
*
* Thread safe.
*
* @param aLast Last resource acquired by calling thread (or 0).
* @param aProposed Resource calling thread proposes to acquire.
* @param aCallContext Calling context whence acquisiton request came.
*/
ResourceAcquisitionArray* CheckAcquisition(const T* aLast,
const T* aProposed,
const CallStack& aCallContext)
{
NS_ASSERTION(aProposed, "null resource");
PRAutoLock _(mLock);
PLHashEntry* second = *GetEntry(aProposed);
OrderingEntry* e = static_cast<OrderingEntry*>(second->value);
if (CallStack::kNone == e->mFirstSeen)
e->mFirstSeen = aCallContext;
if (!aLast)
// don't check if |0 < proposed|; just vamoose
return 0;
PLHashEntry* first = *GetEntry(aLast);
// this is the crux of the deadlock detector algorithm
if (first == second) {
// reflexive deadlock. fastpath b/c InTransitiveClosure is
// not applicable here.
ResourceAcquisitionArray* cycle = new ResourceAcquisitionArray();
if (!cycle)
NS_RUNTIMEABORT("can't allocate dep. cycle array");
cycle->AppendElement(MakeResourceAcquisition(first));
cycle->AppendElement(ResourceAcquisition(aProposed,
aCallContext));
return cycle;
}
if (InTransitiveClosure(first, second)) {
// we've already established |last < proposed|. all is well.
return 0;
}
if (InTransitiveClosure(second, first)) {
// the order |proposed < last| has been deduced, perhaps
// transitively. we're attempting to violate that
// constraint by acquiring resources in the order
// |last < proposed|, and thus we may deadlock under the
// right conditions.
ResourceAcquisitionArray* cycle = GetDeductionChain(second, first);
// show how acquiring |proposed| would complete the cycle
cycle->AppendElement(ResourceAcquisition(aProposed,
aCallContext));
return cycle;
}
// |last|, |proposed| are unordered according to our
// poset. this is fine, but we now need to add this
// ordering constraint.
AddOrder(first, second);
return 0;
}
/**
* Return true iff |aTarget| is in the transitive closure of |aStart|
* over the ordering relation `<_this'.
*
* @precondition |aStart != aTarget|
*/
bool InTransitiveClosure(const PLHashEntry* aStart,
const PLHashEntry* aTarget) const
{
if (IsOrdered(aStart, aTarget))
return true;
index_type i = 0;
size_type len = NumOrders(aStart);
for (const PLHashEntry* const* it = GetOrders(aStart);
i < len; ++i, ++it)
if (InTransitiveClosure(*it, aTarget))
return true;
return false;
}
/**
* Return an array of all resource acquisitions
* aStart <_this r1 <_this r2 <_ ... <_ aTarget
* from which |aStart <_this aTarget| was deduced, including
* |aStart| and |aTarget|.
*
* Nb: there may be multiple deductions of |aStart <_this
* aTarget|. This function returns the first ordering found by
* depth-first search.
*
* Nb: |InTransitiveClosure| could be replaced by this function.
* However, this one is more expensive because we record the DFS
* search stack on the heap whereas the other doesn't.
*
* @precondition |aStart != aTarget|
*/
ResourceAcquisitionArray* GetDeductionChain(
const PLHashEntry* aStart,
const PLHashEntry* aTarget)
{
ResourceAcquisitionArray* chain = new ResourceAcquisitionArray();
if (!chain)
NS_RUNTIMEABORT("can't allocate dep. cycle array");
chain->AppendElement(MakeResourceAcquisition(aStart));
NS_ASSERTION(GetDeductionChain_Helper(aStart, aTarget, chain),
"GetDeductionChain called when there's no deadlock");
return chain;
}
// precondition: |aStart != aTarget|
// invariant: |aStart| is the last element in |aChain|
bool GetDeductionChain_Helper(const PLHashEntry* aStart,
const PLHashEntry* aTarget,
ResourceAcquisitionArray* aChain)
{
if (IsOrdered(aStart, aTarget)) {
aChain->AppendElement(MakeResourceAcquisition(aTarget));
return true;
}
index_type i = 0;
size_type len = NumOrders(aStart);
for (const PLHashEntry* const* it = GetOrders(aStart);
i < len; ++i, ++it) {
aChain->AppendElement(MakeResourceAcquisition(*it));
if (GetDeductionChain_Helper(*it, aTarget, aChain))
return true;
aChain->RemoveElementAt(aChain->Length() - 1);
}
return false;
}
/**
* The partial order on resource acquisitions used by the deadlock
* detector.
*/
PLHashTable* mOrdering; // T* -> PLHashEntry<OrderingEntry>
/**
* Protects contentious methods.
* Nb: can't use mozilla::Mutex since we are used as its deadlock
* detector.
*/
PRLock* mLock;
DeadlockDetector(const DeadlockDetector& aDD);
DeadlockDetector& operator=(const DeadlockDetector& aDD);
};
template<typename T>
const PLHashAllocOps DeadlockDetector<T>::kAllocOps = {
DeadlockDetector<T>::TableAlloc, DeadlockDetector<T>::TableFree,
DeadlockDetector<T>::EntryAlloc, DeadlockDetector<T>::EntryFree
};
template<typename T>
// FIXME bug 456272: tune based on average workload
const PRUint32 DeadlockDetector<T>::kDefaultNumBuckets = 64;
} // namespace mozilla
#endif // ifndef mozilla_DeadlockDetector_h