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annotate rust/hg-cpython/src/cindex.rs @ 41228:3b35ebdb9f8c

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narrow: include working copy narrowspec in transaction journal Now that we have separate narrowspecs for the store and the working copy, we need to include both in the transaction journal. Differential Revision: https://phab.mercurial-scm.org/D5505
author Martin von Zweigbergk <martinvonz@google.com>
date Sat, 29 Dec 2018 22:34:38 -0800
parents ef54bd33b476
children ab0d762d89ef
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1 // cindex.rs
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2 //
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3 // Copyright 2018 Georges Racinet <gracinet@anybox.fr>
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4 //
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5 // This software may be used and distributed according to the terms of the
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6 // GNU General Public License version 2 or any later version.
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7
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8 //! Bindings to use the Index defined by the parsers C extension
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9 //!
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10 //! Ideally, we should use an Index entirely implemented in Rust,
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11 //! but this will take some time to get there.
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12 #[cfg(feature = "python27")]
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13 extern crate python27_sys as python_sys;
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14 #[cfg(feature = "python3")]
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15 extern crate python3_sys as python_sys;
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16
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17 use self::python_sys::PyCapsule_Import;
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18 use cpython::{PyClone, PyErr, PyObject, PyResult, Python};
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19 use hg::{Graph, GraphError, Revision};
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20 use libc::c_int;
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21 use std::ffi::CStr;
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22 use std::mem::transmute;
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23
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24 type IndexParentsFn = unsafe extern "C" fn(
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25 index: *mut python_sys::PyObject,
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26 rev: c_int,
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27 ps: *mut [c_int; 2],
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28 ) -> c_int;
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29
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30 /// A `Graph` backed up by objects and functions from revlog.c
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31 ///
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32 /// This implementation of the `Graph` trait, relies on (pointers to)
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33 /// - the C index object (`index` member)
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34 /// - the `index_get_parents()` function (`parents` member)
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35 ///
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36 /// # Safety
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37 ///
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38 /// The C index itself is mutable, and this Rust exposition is **not
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39 /// protected by the GIL**, meaning that this construct isn't safe with respect
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40 /// to Python threads.
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41 ///
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42 /// All callers of this `Index` must acquire the GIL and must not release it
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43 /// while working.
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44 ///
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45 /// # TODO find a solution to make it GIL safe again.
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46 ///
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47 /// This is non trivial, and can wait until we have a clearer picture with
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48 /// more Rust Mercurial constructs.
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49 ///
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50 /// One possibility would be to a `GILProtectedIndex` wrapper enclosing
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51 /// a `Python<'p>` marker and have it be the one implementing the
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52 /// `Graph` trait, but this would mean the `Graph` implementor would become
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53 /// likely to change between subsequent method invocations of the `hg-core`
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54 /// objects (a serious change of the `hg-core` API):
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55 /// either exposing ways to mutate the `Graph`, or making it a non persistent
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56 /// parameter in the relevant methods that need one.
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57 ///
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58 /// Another possibility would be to introduce an abstract lock handle into
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59 /// the core API, that would be tied to `GILGuard` / `Python<'p>`
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60 /// in the case of the `cpython` crate bindings yet could leave room for other
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61 /// mechanisms in other contexts.
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62 pub struct Index {
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63 index: PyObject,
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64 parents: IndexParentsFn,
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65 }
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66
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67 impl Index {
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68 pub fn new(py: Python, index: PyObject) -> PyResult<Self> {
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69 Ok(Index {
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70 index: index,
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71 parents: decapsule_parents_fn(py)?,
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72 })
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73 }
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74 }
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75
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76 impl Clone for Index {
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77 fn clone(&self) -> Self {
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78 let guard = Python::acquire_gil();
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79 Index {
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80 index: self.index.clone_ref(guard.python()),
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81 parents: self.parents.clone(),
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82 }
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83 }
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84 }
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85
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86 impl Graph for Index {
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87 /// wrap a call to the C extern parents function
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88 fn parents(&self, rev: Revision) -> Result<[Revision; 2], GraphError> {
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89 let mut res: [c_int; 2] = [0; 2];
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90 let code = unsafe {
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91 (self.parents)(
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92 self.index.as_ptr(),
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93 rev as c_int,
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94 &mut res as *mut [c_int; 2],
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95 )
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96 };
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97 match code {
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98 0 => Ok(res),
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99 _ => Err(GraphError::ParentOutOfRange(rev)),
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100 }
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101 }
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102 }
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103
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104 /// Return the `index_get_parents` function of the parsers C Extension module.
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105 ///
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106 /// A pointer to the function is stored in the `parsers` module as a
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107 /// standard [Python capsule](https://docs.python.org/2/c-api/capsule.html).
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108 ///
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109 /// This function retrieves the capsule and casts the function pointer
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110 ///
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111 /// Casting function pointers is one of the rare cases of
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112 /// legitimate use cases of `mem::transmute()` (see
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113 /// https://doc.rust-lang.org/std/mem/fn.transmute.html of
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114 /// `mem::transmute()`.
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115 /// It is inappropriate for architectures where
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116 /// function and data pointer sizes differ (so-called "Harvard
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117 /// architectures"), but these are nowadays mostly DSPs
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118 /// and microcontrollers, hence out of our scope.
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119 fn decapsule_parents_fn(py: Python) -> PyResult<IndexParentsFn> {
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120 unsafe {
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121 let caps_name = CStr::from_bytes_with_nul_unchecked(
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122 b"mercurial.cext.parsers.index_get_parents_CAPI\0",
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123 );
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124 let from_caps = PyCapsule_Import(caps_name.as_ptr(), 0);
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125 if from_caps.is_null() {
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126 return Err(PyErr::fetch(py));
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127 }
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128 Ok(transmute(from_caps))
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129 }
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130 }