From Jason Turner

[propagation]

C++14 → C++17 4.3 KB 53 lines
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Archived: C++14 | C++17
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tmp/tmpnj2yv1sz/{from.md → to.md} RENAMED
@@ -1,12 +1,12 @@
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  ### Exception propagation <a id="propagation">[[propagation]]</a>
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  ``` cpp
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- typedef unspecified exception_ptr;
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  ```
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- The type exception_ptr can be used to refer to an exception object.
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  `exception_ptr` shall satisfy the requirements of
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  `NullablePointer` ([[nullablepointer.requirements]]).
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  Two non-null values of type `exception_ptr` are equivalent and compare
@@ -16,22 +16,24 @@ The default constructor of `exception_ptr` produces the null value of
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  the type.
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  `exception_ptr` shall not be implicitly convertible to any arithmetic,
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  enumeration, or pointer type.
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- An implementation might use a reference-counted smart pointer as
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- `exception_ptr`.
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  For purposes of determining the presence of a data race, operations on
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  `exception_ptr` objects shall access and modify only the `exception_ptr`
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  objects themselves and not the exceptions they refer to. Use of
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  `rethrow_exception` on `exception_ptr` objects that refer to the same
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- exception object shall not introduce a data race. if `rethrow_exception`
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- rethrows the same exception object (rather than a copy), concurrent
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- access to that rethrown exception object may introduce a data race.
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- Changes in the number of `exception_ptr` objects that refer to a
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- particular exception do not introduce a data race.
 
 
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  ``` cpp
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  exception_ptr current_exception() noexcept;
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  ```
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@@ -41,39 +43,45 @@ handled exception, or a null `exception_ptr` object if no exception is
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  being handled. The referenced object shall remain valid at least as long
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  as there is an `exception_ptr` object that refers to it. If the function
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  needs to allocate memory and the attempt fails, it returns an
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  `exception_ptr` object that refers to an instance of `bad_alloc`. It is
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  unspecified whether the return values of two successive calls to
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- `current_exception` refer to the same exception object. That is, it is
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- unspecified whether `current_exception` creates a new copy each time it
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- is called. If the attempt to copy the current exception object throws an
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- exception, the function returns an `exception_ptr` object that refers to
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- the thrown exception or, if this is not possible, to an instance of
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- `bad_exception`. The copy constructor of the thrown exception may also
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- fail, so the implementation is allowed to substitute a `bad_exception`
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- object to avoid infinite recursion.
 
 
 
 
 
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  ``` cpp
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  [[noreturn]] void rethrow_exception(exception_ptr p);
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  ```
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  *Requires:* `p` shall not be a null pointer.
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- *Throws:* the exception object to which `p` refers.
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  ``` cpp
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  template<class E> exception_ptr make_exception_ptr(E e) noexcept;
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  ```
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  *Effects:* Creates an `exception_ptr` object that refers to a copy of
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- `e`, as if
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  ``` cpp
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  try {
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  throw e;
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  } catch(...) {
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  return current_exception();
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  }
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  ```
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- This function is provided for convenience and efficiency reasons.
 
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  ### Exception propagation <a id="propagation">[[propagation]]</a>
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  ``` cpp
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+ using exception_ptr = unspecified;
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  ```
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+ The type `exception_ptr` can be used to refer to an exception object.
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  `exception_ptr` shall satisfy the requirements of
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  `NullablePointer` ([[nullablepointer.requirements]]).
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  Two non-null values of type `exception_ptr` are equivalent and compare
 
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  the type.
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  `exception_ptr` shall not be implicitly convertible to any arithmetic,
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  enumeration, or pointer type.
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+ [*Note 1*: An implementation might use a reference-counted smart
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+ pointer as `exception_ptr`. — *end note*]
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  For purposes of determining the presence of a data race, operations on
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  `exception_ptr` objects shall access and modify only the `exception_ptr`
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  objects themselves and not the exceptions they refer to. Use of
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  `rethrow_exception` on `exception_ptr` objects that refer to the same
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+ exception object shall not introduce a data race.
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+
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+ [*Note 2*: If `rethrow_exception` rethrows the same exception object
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+ (rather than a copy), concurrent access to that rethrown exception
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+ object may introduce a data race. Changes in the number of
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+ `exception_ptr` objects that refer to a particular exception do not
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+ introduce a data race. — *end note*]
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  ``` cpp
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  exception_ptr current_exception() noexcept;
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  ```
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  being handled. The referenced object shall remain valid at least as long
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  as there is an `exception_ptr` object that refers to it. If the function
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  needs to allocate memory and the attempt fails, it returns an
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  `exception_ptr` object that refers to an instance of `bad_alloc`. It is
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  unspecified whether the return values of two successive calls to
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+ `current_exception` refer to the same exception object.
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+
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+ [*Note 3*: That is, it is unspecified whether `current_exception`
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+ creates a new copy each time it is called. — *end note*]
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+
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+ If the attempt to copy the current exception object throws an exception,
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+ the function returns an `exception_ptr` object that refers to the thrown
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+ exception or, if this is not possible, to an instance of
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+ `bad_exception`.
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+
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+ [*Note 4*: The copy constructor of the thrown exception may also fail,
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+ so the implementation is allowed to substitute a `bad_exception` object
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+ to avoid infinite recursion. — *end note*]
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  ``` cpp
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  [[noreturn]] void rethrow_exception(exception_ptr p);
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  ```
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  *Requires:* `p` shall not be a null pointer.
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+ *Throws:* The exception object to which `p` refers.
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  ``` cpp
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  template<class E> exception_ptr make_exception_ptr(E e) noexcept;
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  ```
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  *Effects:* Creates an `exception_ptr` object that refers to a copy of
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+ `e`, as if:
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  ``` cpp
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  try {
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  throw e;
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  } catch(...) {
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  return current_exception();
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  }
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  ```
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+ [*Note 5*: This function is provided for convenience and efficiency
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+ reasons. — *end note*]
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