1 // Copyright (c) 2012 The Chromium Authors. All rights reserved. 2 // Use of this source code is governed by a BSD-style license that can be 3 // found in the LICENSE file. 4 5 #ifndef PPAPI_SHARED_IMPL_PROXY_LOCK_H_ 6 #define PPAPI_SHARED_IMPL_PROXY_LOCK_H_ 7 8 #include "base/basictypes.h" 9 #include "base/bind.h" 10 #include "base/callback.h" 11 #include "base/threading/thread_checker.h" 12 13 #include "ppapi/shared_impl/ppapi_shared_export.h" 14 15 namespace base { 16 class Lock; 17 } 18 19 namespace content { 20 class HostGlobals; 21 } 22 23 namespace ppapi { 24 25 // This is the one lock to rule them all for the ppapi proxy. All PPB interface 26 // functions that need to be synchronized should lock this lock on entry. This 27 // is normally accomplished by using an appropriate Enter RAII object at the 28 // beginning of each thunk function. 29 // 30 // TODO(dmichael): If this turns out to be too slow and contentious, we'll want 31 // to use multiple locks. E.g., one for the var tracker, one for the resource 32 // tracker, etc. 33 class PPAPI_SHARED_EXPORT ProxyLock { 34 public: 35 // Return the global ProxyLock. Normally, you should not access this 36 // directly but instead use ProxyAutoLock or ProxyAutoUnlock. But sometimes 37 // you need access to the ProxyLock, for example to create a condition 38 // variable. 39 static base::Lock* Get(); 40 41 // Acquire the proxy lock. If it is currently held by another thread, block 42 // until it is available. If the lock has not been set using the 'Set' method, 43 // this operation does nothing. That is the normal case for the host side; 44 // see PluginResourceTracker for where the lock gets set for the out-of- 45 // process plugin case. 46 static void Acquire(); 47 // Relinquish the proxy lock. If the lock has not been set, this does nothing. 48 static void Release(); 49 50 // Assert that the lock is owned by the current thread (in the plugin 51 // process). Does nothing when running in-process (or in the host process). 52 static void AssertAcquired(); 53 static void AssertAcquiredDebugOnly() { 54 #ifndef NDEBUG 55 AssertAcquired(); 56 #endif 57 } 58 59 // We have some unit tests where one thread pretends to be the host and one 60 // pretends to be the plugin. This allows the lock to do nothing on only one 61 // thread to support these tests. See TwoWayTest for more information. 62 static void DisableLockingOnThreadForTest(); 63 64 // Enables locking on the current thread. Although locking is enabled by 65 // default, unit tests that rely on the lock being enabled should *still* 66 // call this, since a previous test may have disabled locking. 67 static void EnableLockingOnThreadForTest(); 68 69 private: 70 friend class content::HostGlobals; 71 // On the host side, we do not lock. This must be called at most once at 72 // startup, before other threads that may access the ProxyLock have had a 73 // chance to run. 74 static void DisableLocking(); 75 76 DISALLOW_IMPLICIT_CONSTRUCTORS(ProxyLock); 77 }; 78 79 // A simple RAII class for locking the PPAPI proxy lock on entry and releasing 80 // on exit. This is for simple interfaces that don't use the 'thunk' system, 81 // such as PPB_Var and PPB_Core. 82 class ProxyAutoLock { 83 public: 84 ProxyAutoLock() { ProxyLock::Acquire(); } 85 ~ProxyAutoLock() { ProxyLock::Release(); } 86 87 private: 88 DISALLOW_COPY_AND_ASSIGN(ProxyAutoLock); 89 }; 90 91 // The inverse of the above; unlock on construction, lock on destruction. This 92 // is useful for calling out to the plugin, when we need to unlock but ensure 93 // that we re-acquire the lock when the plugin is returns or raises an 94 // exception. 95 class ProxyAutoUnlock { 96 public: 97 ProxyAutoUnlock() { ProxyLock::Release(); } 98 ~ProxyAutoUnlock() { ProxyLock::Acquire(); } 99 100 private: 101 DISALLOW_COPY_AND_ASSIGN(ProxyAutoUnlock); 102 }; 103 104 // A set of function template overloads for invoking a function pointer while 105 // the ProxyLock is unlocked. This assumes that the luck is held. 106 // CallWhileUnlocked unlocks the ProxyLock just before invoking the given 107 // function. The lock is immediately re-acquired when the invoked function 108 // function returns. CallWhileUnlocked returns whatever the given function 109 // returned. 110 // 111 // Example usage: 112 // *result = CallWhileUnlocked(ppp_input_event_impl_->HandleInputEvent, 113 // instance, 114 // resource->pp_resource()); 115 template <class ReturnType> 116 ReturnType CallWhileUnlocked(ReturnType (*function)()) { 117 ProxyAutoUnlock unlock; 118 return function(); 119 } 120 template <class ReturnType, class P1> 121 ReturnType CallWhileUnlocked(ReturnType (*function)(P1), const P1& p1) { 122 ProxyAutoUnlock unlock; 123 return function(p1); 124 } 125 template <class ReturnType, class P1, class P2> 126 ReturnType CallWhileUnlocked(ReturnType (*function)(P1, P2), 127 const P1& p1, 128 const P2& p2) { 129 ProxyAutoUnlock unlock; 130 return function(p1, p2); 131 } 132 template <class ReturnType, class P1, class P2, class P3> 133 ReturnType CallWhileUnlocked(ReturnType (*function)(P1, P2, P3), 134 const P1& p1, 135 const P2& p2, 136 const P3& p3) { 137 ProxyAutoUnlock unlock; 138 return function(p1, p2, p3); 139 } 140 template <class ReturnType, class P1, class P2, class P3, class P4> 141 ReturnType CallWhileUnlocked(ReturnType (*function)(P1, P2, P3, P4), 142 const P1& p1, 143 const P2& p2, 144 const P3& p3, 145 const P4& p4) { 146 ProxyAutoUnlock unlock; 147 return function(p1, p2, p3, p4); 148 } 149 template <class ReturnType, class P1, class P2, class P3, class P4, class P5> 150 ReturnType CallWhileUnlocked(ReturnType (*function)(P1, P2, P3, P4, P5), 151 const P1& p1, 152 const P2& p2, 153 const P3& p3, 154 const P4& p4, 155 const P5& p5) { 156 ProxyAutoUnlock unlock; 157 return function(p1, p2, p3, p4, p5); 158 } 159 void PPAPI_SHARED_EXPORT CallWhileUnlocked(const base::Closure& closure); 160 161 namespace internal { 162 163 template <typename RunType> 164 class RunWhileLockedHelper; 165 166 template <> 167 class RunWhileLockedHelper<void()> { 168 public: 169 typedef base::Callback<void()> CallbackType; 170 explicit RunWhileLockedHelper(const CallbackType& callback) 171 : callback_(new CallbackType(callback)) { 172 // Copying |callback| may adjust reference counts for bound Vars or 173 // Resources; we should have the lock already. 174 ProxyLock::AssertAcquired(); 175 // CallWhileLocked and destruction might happen on a different thread from 176 // creation. 177 thread_checker_.DetachFromThread(); 178 } 179 void CallWhileLocked() { 180 // Bind thread_checker_ to this thread so we can check in the destructor. 181 DCHECK(thread_checker_.CalledOnValidThread()); 182 ProxyAutoLock lock; 183 { 184 // Use a scope and local Callback to ensure that the callback is cleared 185 // before the lock is released, even in the unlikely event that Run() 186 // throws an exception. 187 scoped_ptr<CallbackType> temp_callback(callback_.Pass()); 188 temp_callback->Run(); 189 } 190 } 191 192 ~RunWhileLockedHelper() { 193 // Check that the Callback is destroyed on the same thread as where 194 // CallWhileLocked happened (if CallWhileLocked happened). 195 DCHECK(thread_checker_.CalledOnValidThread()); 196 // Here we read callback_ without the lock. This is why the callback must be 197 // destroyed on the same thread where it runs. There are 2 cases where 198 // callback_ will be NULL: 199 // 1) This is the original RunWhileLockedHelper that RunWhileLocked 200 // created. When it was copied somewhere else (e.g., to a MessageLoop 201 // queue), callback_ was passed to the new copy, and the original 202 // RunWhileLockedHelper's callback_ was set to NULL (since scoped_ptrs 203 // only ever have 1 owner). In this case, we don't want to acquire the 204 // lock, because we already have it. 205 // 2) callback_ has already been run via CallWhileLocked. In this case, 206 // there's no need to acquire the lock, because we don't touch any 207 // shared data. 208 if (callback_) { 209 // If the callback was not run, we still need to have the lock when we 210 // destroy the callback in case it had a Resource bound to it. This 211 // ensures that the Resource's destructor is invoked only with the lock 212 // held. 213 // 214 // Also: Resource and Var inherit RefCounted (not ThreadSafeRefCounted), 215 // and these callbacks need to be usable on any thread. So we need to lock 216 // when releasing the callback to avoid ref counting races. 217 ProxyAutoLock lock; 218 callback_.reset(); 219 } 220 } 221 222 private: 223 scoped_ptr<CallbackType> callback_; 224 225 // Used to ensure that the Callback is run and deleted on the same thread. 226 base::ThreadChecker thread_checker_; 227 }; 228 229 template <typename P1> 230 class RunWhileLockedHelper<void(P1)> { 231 public: 232 typedef base::Callback<void(P1)> CallbackType; 233 explicit RunWhileLockedHelper(const CallbackType& callback) 234 : callback_(new CallbackType(callback)) { 235 ProxyLock::AssertAcquired(); 236 thread_checker_.DetachFromThread(); 237 } 238 void CallWhileLocked(P1 p1) { 239 DCHECK(thread_checker_.CalledOnValidThread()); 240 ProxyAutoLock lock; 241 { 242 scoped_ptr<CallbackType> temp_callback(callback_.Pass()); 243 temp_callback->Run(p1); 244 } 245 } 246 ~RunWhileLockedHelper() { 247 DCHECK(thread_checker_.CalledOnValidThread()); 248 if (callback_) { 249 ProxyAutoLock lock; 250 callback_.reset(); 251 } 252 } 253 254 private: 255 scoped_ptr<CallbackType> callback_; 256 base::ThreadChecker thread_checker_; 257 }; 258 259 template <typename P1, typename P2> 260 class RunWhileLockedHelper<void(P1, P2)> { 261 public: 262 typedef base::Callback<void(P1, P2)> CallbackType; 263 explicit RunWhileLockedHelper(const CallbackType& callback) 264 : callback_(new CallbackType(callback)) { 265 ProxyLock::AssertAcquired(); 266 thread_checker_.DetachFromThread(); 267 } 268 void CallWhileLocked(P1 p1, P2 p2) { 269 DCHECK(thread_checker_.CalledOnValidThread()); 270 ProxyAutoLock lock; 271 { 272 scoped_ptr<CallbackType> temp_callback(callback_.Pass()); 273 temp_callback->Run(p1, p2); 274 } 275 } 276 ~RunWhileLockedHelper() { 277 DCHECK(thread_checker_.CalledOnValidThread()); 278 if (callback_) { 279 ProxyAutoLock lock; 280 callback_.reset(); 281 } 282 } 283 284 private: 285 scoped_ptr<CallbackType> callback_; 286 base::ThreadChecker thread_checker_; 287 }; 288 289 template <typename P1, typename P2, typename P3> 290 class RunWhileLockedHelper<void(P1, P2, P3)> { 291 public: 292 typedef base::Callback<void(P1, P2, P3)> CallbackType; 293 explicit RunWhileLockedHelper(const CallbackType& callback) 294 : callback_(new CallbackType(callback)) { 295 ProxyLock::AssertAcquired(); 296 thread_checker_.DetachFromThread(); 297 } 298 void CallWhileLocked(P1 p1, P2 p2, P3 p3) { 299 DCHECK(thread_checker_.CalledOnValidThread()); 300 ProxyAutoLock lock; 301 { 302 scoped_ptr<CallbackType> temp_callback(callback_.Pass()); 303 temp_callback->Run(p1, p2, p3); 304 } 305 } 306 ~RunWhileLockedHelper() { 307 DCHECK(thread_checker_.CalledOnValidThread()); 308 if (callback_) { 309 ProxyAutoLock lock; 310 callback_.reset(); 311 } 312 } 313 314 private: 315 scoped_ptr<CallbackType> callback_; 316 base::ThreadChecker thread_checker_; 317 }; 318 319 } // namespace internal 320 321 // RunWhileLocked wraps the given Callback in a new Callback that, when invoked: 322 // 1) Locks the ProxyLock. 323 // 2) Runs the original Callback (forwarding arguments, if any). 324 // 3) Clears the original Callback (while the lock is held). 325 // 4) Unlocks the ProxyLock. 326 // Note that it's important that the callback is cleared in step (3), in case 327 // clearing the Callback causes a destructor (e.g., for a Resource) to run, 328 // which should hold the ProxyLock to avoid data races. 329 // 330 // This is for cases where you want to run a task or store a Callback, but you 331 // want to ensure that the ProxyLock is acquired for the duration of the task 332 // that the Callback runs. 333 // EXAMPLE USAGE: 334 // GetMainThreadMessageLoop()->PostDelayedTask( 335 // FROM_HERE, 336 // RunWhileLocked(base::Bind(&CallbackWrapper, callback, result)), 337 // delay_in_ms); 338 // 339 // In normal usage like the above, this all should "just work". However, if you 340 // do something unusual, you may get a runtime crash due to deadlock. Here are 341 // the ways that the returned Callback must be used to avoid a deadlock: 342 // (1) copied to another Callback. After that, the original callback can be 343 // destroyed with or without the proxy lock acquired, while the newly assigned 344 // callback has to conform to these same restrictions. Or 345 // (2) run without proxy lock acquired (e.g., being posted to a MessageLoop 346 // and run there). The callback must be destroyed on the same thread where it 347 // was run (but can be destroyed with or without the proxy lock acquired). Or 348 // (3) destroyed without the proxy lock acquired. 349 template <class FunctionType> 350 inline base::Callback<FunctionType> RunWhileLocked( 351 const base::Callback<FunctionType>& callback) { 352 internal::RunWhileLockedHelper<FunctionType>* helper = 353 new internal::RunWhileLockedHelper<FunctionType>(callback); 354 return base::Bind( 355 &internal::RunWhileLockedHelper<FunctionType>::CallWhileLocked, 356 base::Owned(helper)); 357 } 358 359 } // namespace ppapi 360 361 #endif // PPAPI_SHARED_IMPL_PROXY_LOCK_H_ 362