1 //
2 // Copyright 2019 The Abseil Authors.
3 //
4 // Licensed under the Apache License, Version 2.0 (the "License");
5 // you may not use this file except in compliance with the License.
6 // You may obtain a copy of the License at
7 //
8 //      https://www.apache.org/licenses/LICENSE-2.0
9 //
10 // Unless required by applicable law or agreed to in writing, software
11 // distributed under the License is distributed on an "AS IS" BASIS,
12 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 // See the License for the specific language governing permissions and
14 // limitations under the License.
15 #include "absl/flags/usage.h"
16 
17 #include <stdlib.h>
18 
19 #include <string>
20 
21 #include "absl/base/attributes.h"
22 #include "absl/base/config.h"
23 #include "absl/base/const_init.h"
24 #include "absl/base/thread_annotations.h"
25 #include "absl/flags/internal/usage.h"
26 #include "absl/strings/string_view.h"
27 #include "absl/synchronization/mutex.h"
28 
29 namespace absl {
30 ABSL_NAMESPACE_BEGIN
31 namespace flags_internal {
32 namespace {
33 ABSL_CONST_INIT absl::Mutex usage_message_guard(absl::kConstInit);
34 ABSL_CONST_INIT std::string* program_usage_message
35     ABSL_GUARDED_BY(usage_message_guard) = nullptr;
36 }  // namespace
37 }  // namespace flags_internal
38 
39 // --------------------------------------------------------------------
40 // Sets the "usage" message to be used by help reporting routines.
SetProgramUsageMessage(absl::string_view new_usage_message)41 void SetProgramUsageMessage(absl::string_view new_usage_message) {
42   absl::MutexLock l(&flags_internal::usage_message_guard);
43 
44   if (flags_internal::program_usage_message != nullptr) {
45     ABSL_INTERNAL_LOG(FATAL, "SetProgramUsageMessage() called twice.");
46     std::exit(1);
47   }
48 
49   flags_internal::program_usage_message = new std::string(new_usage_message);
50 }
51 
52 // --------------------------------------------------------------------
53 // Returns the usage message set by SetProgramUsageMessage().
54 // Note: We able to return string_view here only because calling
55 // SetProgramUsageMessage twice is prohibited.
ProgramUsageMessage()56 absl::string_view ProgramUsageMessage() {
57   absl::MutexLock l(&flags_internal::usage_message_guard);
58 
59   return flags_internal::program_usage_message != nullptr
60              ? absl::string_view(*flags_internal::program_usage_message)
61              : "Warning: SetProgramUsageMessage() never called";
62 }
63 
64 ABSL_NAMESPACE_END
65 }  // namespace absl
66