| Directory: | cvmfs/ |
|---|---|
| File: | cvmfs/util/future.h |
| Date: | 2024-04-21 02:33:16 |
| Exec | Total | Coverage | |
|---|---|---|---|
| Lines: | 27 | 30 | 90.0% |
| Branches: | 8 | 14 | 57.1% |
| Line | Branch | Exec | Source |
|---|---|---|---|
| 1 | /** | ||
| 2 | * This file is part of the CernVM File System. | ||
| 3 | */ | ||
| 4 | |||
| 5 | #ifndef CVMFS_UTIL_FUTURE_H_ | ||
| 6 | #define CVMFS_UTIL_FUTURE_H_ | ||
| 7 | |||
| 8 | #include <pthread.h> | ||
| 9 | |||
| 10 | #include <cassert> | ||
| 11 | |||
| 12 | #include "util/mutex.h" | ||
| 13 | #include "util/single_copy.h" | ||
| 14 | |||
| 15 | #ifdef CVMFS_NAMESPACE_GUARD | ||
| 16 | namespace CVMFS_NAMESPACE_GUARD { | ||
| 17 | #endif | ||
| 18 | |||
| 19 | /** | ||
| 20 | * This is a simple implementation of a Future wrapper template. | ||
| 21 | * It is used as a proxy for results that are computed asynchronously and might | ||
| 22 | * not be available on the first access. | ||
| 23 | * Since this is a very simple implementation one needs to use the Future's | ||
| 24 | * Get() and Set() methods to obtain the containing data resp. to write it. | ||
| 25 | * Note: More than a single call to Set() is prohibited! | ||
| 26 | * If Get() is called before Set() the calling thread will block until | ||
| 27 | * the value has been set by a different thread. | ||
| 28 | * | ||
| 29 | * @param T the value type wrapped by this Future template | ||
| 30 | */ | ||
| 31 | template <typename T> | ||
| 32 | class Future : SingleCopy { | ||
| 33 | public: | ||
| 34 | 51 | Future() : object_was_set_(false) { | |
| 35 | 51 | int retval = pthread_mutex_init(&mutex_, NULL); | |
| 36 |
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51 | assert(retval == 0); |
| 37 | 51 | retval = pthread_cond_init(&object_set_, NULL); | |
| 38 |
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51 | assert(retval == 0); |
| 39 | 51 | } | |
| 40 | |||
| 41 | 51 | ~Future() { | |
| 42 | 51 | int retval = pthread_cond_destroy(&object_set_); | |
| 43 |
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51 | assert(retval == 0); |
| 44 | 51 | retval = pthread_mutex_destroy(&mutex_); | |
| 45 |
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51 | assert(retval == 0); |
| 46 | 51 | } | |
| 47 | |||
| 48 | /** | ||
| 49 | * Save an asynchronously computed value into the Future. This potentially | ||
| 50 | * unblocks threads that already wait for the value. | ||
| 51 | * @param object the value object to be set | ||
| 52 | */ | ||
| 53 | 51 | void Set(const T &object) { | |
| 54 | 51 | MutexLockGuard guard(mutex_); | |
| 55 |
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51 | assert(!object_was_set_); |
| 56 | 51 | object_ = object; | |
| 57 | 51 | object_was_set_ = true; | |
| 58 | 51 | pthread_cond_broadcast(&object_set_); | |
| 59 | 51 | } | |
| 60 | |||
| 61 | /** | ||
| 62 | * Retrieves the wrapped value object. If the value is not yet available it | ||
| 63 | * will automatically block until a different thread calls Set(). | ||
| 64 | * @return the containing value object | ||
| 65 | */ | ||
| 66 | 51 | T& Get() { | |
| 67 | 51 | Wait(); | |
| 68 | 51 | return object_; | |
| 69 | } | ||
| 70 | |||
| 71 | ✗ | const T& Get() const { | |
| 72 | ✗ | Wait(); | |
| 73 | ✗ | return object_; | |
| 74 | } | ||
| 75 | |||
| 76 | private: | ||
| 77 | 51 | void Wait() const { | |
| 78 | 51 | MutexLockGuard guard(mutex_); | |
| 79 |
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78 | while (!object_was_set_) { |
| 80 |
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27 | pthread_cond_wait(&object_set_, &mutex_); |
| 81 | } | ||
| 82 | 51 | } | |
| 83 | |||
| 84 | T object_; | ||
| 85 | mutable pthread_mutex_t mutex_; | ||
| 86 | mutable pthread_cond_t object_set_; | ||
| 87 | bool object_was_set_; | ||
| 88 | }; | ||
| 89 | |||
| 90 | #ifdef CVMFS_NAMESPACE_GUARD | ||
| 91 | } // namespace CVMFS_NAMESPACE_GUARD | ||
| 92 | #endif | ||
| 93 | |||
| 94 | #endif // CVMFS_UTIL_FUTURE_H_ | ||
| 95 |