thread_identity.h
Go to the documentation of this file.
1 // Copyright 2017 The Abseil Authors.
2 //
3 // Licensed under the Apache License, Version 2.0 (the "License");
4 // you may not use this file except in compliance with the License.
5 // You may obtain a copy of the License at
6 //
7 // https://www.apache.org/licenses/LICENSE-2.0
8 //
9 // Unless required by applicable law or agreed to in writing, software
10 // distributed under the License is distributed on an "AS IS" BASIS,
11 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
12 // See the License for the specific language governing permissions and
13 // limitations under the License.
14 //
15 // Each active thread has an ThreadIdentity that may represent the thread in
16 // various level interfaces. ThreadIdentity objects are never deallocated.
17 // When a thread terminates, its ThreadIdentity object may be reused for a
18 // thread created later.
19 
20 #ifndef ABSL_BASE_INTERNAL_THREAD_IDENTITY_H_
21 #define ABSL_BASE_INTERNAL_THREAD_IDENTITY_H_
22 
23 #ifndef _WIN32
24 #include <pthread.h>
25 // Defines __GOOGLE_GRTE_VERSION__ (via glibc-specific features.h) when
26 // supported.
27 #include <unistd.h>
28 #endif
29 
30 #include <atomic>
31 #include <cstdint>
32 
34 
35 namespace absl {
36 
37 struct SynchLocksHeld;
38 struct SynchWaitParams;
39 
40 namespace base_internal {
41 
42 class SpinLock;
43 struct ThreadIdentity;
44 
45 // Used by the implementation of absl::Mutex and absl::CondVar.
47  // The internal representation of absl::Mutex and absl::CondVar rely
48  // on the alignment of PerThreadSynch. Both store the address of the
49  // PerThreadSynch in the high-order bits of their internal state,
50  // which means the low kLowZeroBits of the address of PerThreadSynch
51  // must be zero.
52  static constexpr int kLowZeroBits = 8;
53  static constexpr int kAlignment = 1 << kLowZeroBits;
54 
55  // Returns the associated ThreadIdentity.
56  // This can be implemented as a cast because we guarantee
57  // PerThreadSynch is the first element of ThreadIdentity.
59  return reinterpret_cast<ThreadIdentity*>(this);
60  }
61 
62  PerThreadSynch *next; // Circular waiter queue; initialized to 0.
63  PerThreadSynch *skip; // If non-zero, all entries in Mutex queue
64  // up to and including "skip" have same
65  // condition as this, and will be woken later
66  bool may_skip; // if false while on mutex queue, a mutex unlocker
67  // is using this PerThreadSynch as a terminator. Its
68  // skip field must not be filled in because the loop
69  // might then skip over the terminator.
70 
71  // The wait parameters of the current wait. waitp is null if the
72  // thread is not waiting. Transitions from null to non-null must
73  // occur before the enqueue commit point (state = kQueued in
74  // Enqueue() and CondVarEnqueue()). Transitions from non-null to
75  // null must occur after the wait is finished (state = kAvailable in
76  // Mutex::Block() and CondVar::WaitCommon()). This field may be
77  // changed only by the thread that describes this PerThreadSynch. A
78  // special case is Fer(), which calls Enqueue() on another thread,
79  // but with an identical SynchWaitParams pointer, thus leaving the
80  // pointer unchanged.
82 
83  bool suppress_fatal_errors; // If true, try to proceed even in the face of
84  // broken invariants. This is used within fatal
85  // signal handlers to improve the chances of
86  // debug logging information being output
87  // successfully.
88 
89  intptr_t readers; // Number of readers in mutex.
90  int priority; // Priority of thread (updated every so often).
91 
92  // When priority will next be read (cycles).
94 
95  // State values:
96  // kAvailable: This PerThreadSynch is available.
97  // kQueued: This PerThreadSynch is unavailable, it's currently queued on a
98  // Mutex or CondVar waistlist.
99  //
100  // Transitions from kQueued to kAvailable require a release
101  // barrier. This is needed as a waiter may use "state" to
102  // independently observe that it's no longer queued.
103  //
104  // Transitions from kAvailable to kQueued require no barrier, they
105  // are externally ordered by the Mutex.
106  enum State {
109  };
110  std::atomic<State> state;
111 
112  bool maybe_unlocking; // Valid at head of Mutex waiter queue;
113  // true if UnlockSlow could be searching
114  // for a waiter to wake. Used for an optimization
115  // in Enqueue(). true is always a valid value.
116  // Can be reset to false when the unlocker or any
117  // writer releases the lock, or a reader fully releases
118  // the lock. It may not be set to false by a reader
119  // that decrements the count to non-zero.
120  // protected by mutex spinlock
121 
122  bool wake; // This thread is to be woken from a Mutex.
123 
124  // If "x" is on a waiter list for a mutex, "x->cond_waiter" is true iff the
125  // waiter is waiting on the mutex as part of a CV Wait or Mutex Await.
126  //
127  // The value of "x->cond_waiter" is meaningless if "x" is not on a
128  // Mutex waiter list.
130 
131  // Locks held; used during deadlock detection.
132  // Allocated in Synch_GetAllLocks() and freed in ReclaimThreadIdentity().
134 };
135 
137  // Must be the first member. The Mutex implementation requires that
138  // the PerThreadSynch object associated with each thread is
139  // PerThreadSynch::kAlignment aligned. We provide this alignment on
140  // ThreadIdentity itself.
142 
143  // Private: Reserved for absl::synchronization_internal::Waiter.
144  struct WaiterState {
145  char data[128];
146  } waiter_state;
147 
148  // Used by PerThreadSem::{Get,Set}ThreadBlockedCounter().
149  std::atomic<int>* blocked_count_ptr;
150 
151  // The following variables are mostly read/written just by the
152  // thread itself. The only exception is that these are read by
153  // a ticker thread as a hint.
154  std::atomic<int> ticker; // Tick counter, incremented once per second.
155  std::atomic<int> wait_start; // Ticker value when thread started waiting.
156  std::atomic<bool> is_idle; // Has thread become idle yet?
157 
159 };
160 
161 // Returns the ThreadIdentity object representing the calling thread; guaranteed
162 // to be unique for its lifetime. The returned object will remain valid for the
163 // program's lifetime; although it may be re-assigned to a subsequent thread.
164 // If one does not exist, return nullptr instead.
165 //
166 // Does not malloc(*), and is async-signal safe.
167 // [*] Technically pthread_setspecific() does malloc on first use; however this
168 // is handled internally within tcmalloc's initialization already.
169 //
170 // New ThreadIdentity objects can be constructed and associated with a thread
171 // by calling GetOrCreateCurrentThreadIdentity() in per-thread-sem.h.
173 
174 using ThreadIdentityReclaimerFunction = void (*)(void*);
175 
176 // Sets the current thread identity to the given value. 'reclaimer' is a
177 // pointer to the global function for cleaning up instances on thread
178 // destruction.
181 
182 // Removes the currently associated ThreadIdentity from the running thread.
183 // This must be called from inside the ThreadIdentityReclaimerFunction, and only
184 // from that function.
186 
187 // May be chosen at compile time via: -DABSL_FORCE_THREAD_IDENTITY_MODE=<mode
188 // index>
189 #ifdef ABSL_THREAD_IDENTITY_MODE_USE_POSIX_SETSPECIFIC
190 #error ABSL_THREAD_IDENTITY_MODE_USE_POSIX_SETSPECIFIC cannot be direcly set
191 #else
192 #define ABSL_THREAD_IDENTITY_MODE_USE_POSIX_SETSPECIFIC 0
193 #endif
194 
195 #ifdef ABSL_THREAD_IDENTITY_MODE_USE_TLS
196 #error ABSL_THREAD_IDENTITY_MODE_USE_TLS cannot be direcly set
197 #else
198 #define ABSL_THREAD_IDENTITY_MODE_USE_TLS 1
199 #endif
200 
201 #ifdef ABSL_THREAD_IDENTITY_MODE_USE_CPP11
202 #error ABSL_THREAD_IDENTITY_MODE_USE_CPP11 cannot be direcly set
203 #else
204 #define ABSL_THREAD_IDENTITY_MODE_USE_CPP11 2
205 #endif
206 
207 #ifdef ABSL_THREAD_IDENTITY_MODE
208 #error ABSL_THREAD_IDENTITY_MODE cannot be direcly set
209 #elif defined(ABSL_FORCE_THREAD_IDENTITY_MODE)
210 #define ABSL_THREAD_IDENTITY_MODE ABSL_FORCE_THREAD_IDENTITY_MODE
211 #elif defined(_WIN32)
212 #define ABSL_THREAD_IDENTITY_MODE ABSL_THREAD_IDENTITY_MODE_USE_CPP11
213 #elif ABSL_PER_THREAD_TLS && defined(__GOOGLE_GRTE_VERSION__) && \
214  (__GOOGLE_GRTE_VERSION__ >= 20140228L)
215 // Support for async-safe TLS was specifically added in GRTEv4. It's not
216 // present in the upstream eglibc.
217 // Note: Current default for production systems.
218 #define ABSL_THREAD_IDENTITY_MODE ABSL_THREAD_IDENTITY_MODE_USE_TLS
219 #else
220 #define ABSL_THREAD_IDENTITY_MODE \
221  ABSL_THREAD_IDENTITY_MODE_USE_POSIX_SETSPECIFIC
222 #endif
223 
224 #if ABSL_THREAD_IDENTITY_MODE == ABSL_THREAD_IDENTITY_MODE_USE_TLS || \
225  ABSL_THREAD_IDENTITY_MODE == ABSL_THREAD_IDENTITY_MODE_USE_CPP11
226 
227 extern ABSL_PER_THREAD_TLS_KEYWORD ThreadIdentity* thread_identity_ptr;
228 
229 inline ThreadIdentity* CurrentThreadIdentityIfPresent() {
230  return thread_identity_ptr;
231 }
232 
233 #elif ABSL_THREAD_IDENTITY_MODE != \
234  ABSL_THREAD_IDENTITY_MODE_USE_POSIX_SETSPECIFIC
235 #error Unknown ABSL_THREAD_IDENTITY_MODE
236 #endif
237 
238 } // namespace base_internal
239 } // namespace absl
240 
241 #endif // ABSL_BASE_INTERNAL_THREAD_IDENTITY_H_
ABSL_PER_THREAD_TLS_KEYWORD ThreadIdentity * thread_identity_ptr
void(*)(void *) ThreadIdentityReclaimerFunction
ThreadIdentity * CurrentThreadIdentityIfPresent()
std::atomic< int > * blocked_count_ptr
Definition: algorithm.h:29
static char data[kDataSize]
Definition: city_test.cc:31
void SetCurrentThreadIdentity(ThreadIdentity *identity, ThreadIdentityReclaimerFunction reclaimer)
#define ABSL_PER_THREAD_TLS_KEYWORD


abseil_cpp
Author(s):
autogenerated on Tue Jun 18 2019 19:44:37