1 // Copyright 2021 gRPC 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 //     http://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 #ifndef GRPC_SRC_CORE_LIB_SLICE_SLICE_REFCOUNT_H
16 #define GRPC_SRC_CORE_LIB_SLICE_SLICE_REFCOUNT_H
17 
18 #include <grpc/support/port_platform.h>
19 
20 #include <inttypes.h>
21 #include <stddef.h>
22 
23 #include <atomic>
24 
25 #include <grpc/support/log.h>
26 
27 #include "src/core/lib/debug/trace.h"
28 #include "src/core/lib/gprpp/debug_location.h"
29 
30 extern grpc_core::DebugOnlyTraceFlag grpc_slice_refcount_trace;
31 
32 // grpc_slice_refcount : A reference count for grpc_slice.
33 struct grpc_slice_refcount {
34  public:
35   typedef void (*DestroyerFn)(grpc_slice_refcount*);
36 
NoopRefcountgrpc_slice_refcount37   static grpc_slice_refcount* NoopRefcount() {
38     return reinterpret_cast<grpc_slice_refcount*>(1);
39   }
40 
41   grpc_slice_refcount() = default;
42 
43   // Regular constructor for grpc_slice_refcount.
44   //
45   // Parameters:
46   //  1. DestroyerFn destroyer_fn
47   //  Called when the refcount goes to 0, with 'this' as parameter.
grpc_slice_refcountgrpc_slice_refcount48   explicit grpc_slice_refcount(DestroyerFn destroyer_fn)
49       : destroyer_fn_(destroyer_fn) {}
50 
Refgrpc_slice_refcount51   void Ref(grpc_core::DebugLocation location) {
52     auto prev_refs = ref_.fetch_add(1, std::memory_order_relaxed);
53     if (grpc_slice_refcount_trace.enabled()) {
54       gpr_log(location.file(), location.line(), GPR_LOG_SEVERITY_INFO,
55               "REF %p %" PRIdPTR "->%" PRIdPTR, this, prev_refs, prev_refs + 1);
56     }
57   }
Unrefgrpc_slice_refcount58   void Unref(grpc_core::DebugLocation location) {
59     auto prev_refs = ref_.fetch_sub(1, std::memory_order_acq_rel);
60     if (grpc_slice_refcount_trace.enabled()) {
61       gpr_log(location.file(), location.line(), GPR_LOG_SEVERITY_INFO,
62               "UNREF %p %" PRIdPTR "->%" PRIdPTR, this, prev_refs,
63               prev_refs - 1);
64     }
65     if (prev_refs == 1) {
66       destroyer_fn_(this);
67     }
68   }
69 
70   // Is this the only instance?
71   // For this to be useful the caller needs to ensure that if this is the only
72   // instance, no other instance could be created during this call.
IsUniquegrpc_slice_refcount73   bool IsUnique() const { return ref_.load(std::memory_order_relaxed) == 1; }
74 
75  private:
76   std::atomic<size_t> ref_{1};
77   DestroyerFn destroyer_fn_ = nullptr;
78 };
79 
80 #endif  // GRPC_SRC_CORE_LIB_SLICE_SLICE_REFCOUNT_H
81