Torne (Richard Coles) | 5821806 | 2012-11-14 11:43:16 +0000 | [diff] [blame] | 1 | // Copyright (c) 2012 The Chromium Authors. All rights reserved. |
| 2 | // Use of this source code is governed by a BSD-style license that can be |
| 3 | // found in the LICENSE file. |
| 4 | |
| 5 | #ifndef PPAPI_CPP_INSTANCE_HANDLE_H_ |
| 6 | #define PPAPI_CPP_INSTANCE_HANDLE_H_ |
| 7 | |
| 8 | #include "ppapi/c/pp_instance.h" |
| 9 | |
| 10 | |
| 11 | /// @file |
| 12 | /// This file defines an instance handle used to identify an instance in a |
| 13 | /// constructor for a resource. |
| 14 | namespace pp { |
| 15 | |
| 16 | class Instance; |
| 17 | |
| 18 | /// An instance handle identifies an instance in a constructor for a resource. |
| 19 | /// This class solves two different problems: |
| 20 | /// |
| 21 | /// 1. A pp::Instance object's lifetime is managed by the system on the main |
| 22 | /// pepper thread of the module. This means that it may get destroyed at any |
| 23 | /// time based on something that happens on the web page. Therefore, it's not |
| 24 | /// safe to refer to a <code>pp::Instance</code> object on a background thread. |
| 25 | /// Instead, we need to pass some kind of identifier to resource constructors |
| 26 | /// so that they may safely be used on background threads. If the instance |
| 27 | /// becomes invalid, the resource creation will fail on the background thread, |
| 28 | /// but it won't crash. |
| 29 | /// |
| 30 | /// 2. <code>PP_Instance</code> would be a good identifier to use for this case. |
| 31 | /// However, using <code>PP_Instance</code> in the constructor to resources is |
| 32 | /// problematic because it is just a typedef for an integer, as is a |
| 33 | /// <code>PP_Resource</code>. Many resources have alternate constructors that |
| 34 | /// just take an existing <code>PP_Resource</code>, so the constructors would |
| 35 | /// be ambiguous. Having this wrapper around a <code>PP_Instance</code> |
| 36 | /// prevents this ambiguity, and also provides a nice place to consolidate an |
| 37 | /// implicit conversion from <code>pp::Instance*</code> for prettier code on |
| 38 | /// the main thread (you can just pass "this" to resource constructors in your |
| 39 | /// instance objects). |
| 40 | /// |
| 41 | /// You should always pass an <code>InstanceHandle</code> to background threads |
| 42 | /// instead of a <code>pp::Instance</code>, and use them in resource |
| 43 | /// constructors and code that may be used from background threads. |
| 44 | class InstanceHandle { |
| 45 | public: |
| 46 | /// Implicit constructor for converting a <code>pp::Instance</code> to an |
| 47 | /// instance handle. |
| 48 | /// |
| 49 | /// @param[in] instance The instance with which this |
| 50 | /// <code>InstanceHandle</code> will be associated. |
| 51 | InstanceHandle(Instance* instance); |
| 52 | |
| 53 | /// This constructor explicitly converts a <code>PP_Instance</code> to an |
| 54 | /// instance handle. This should not be implicit because it can make some |
| 55 | /// resource constructors ambiguous. <code>PP_Instance</code> is just a |
| 56 | /// typedef for an integer, as is <code>PP_Resource</code>, so the compiler |
| 57 | /// can get confused between the two. |
| 58 | /// |
| 59 | /// @param[in] pp_instance The instance with which this |
| 60 | /// <code>InstanceHandle</code> will be associated. |
| 61 | explicit InstanceHandle(PP_Instance pp_instance) |
| 62 | : pp_instance_(pp_instance) {} |
| 63 | |
| 64 | /// The pp_instance() function returns the <code>PP_Instance</code>. |
| 65 | /// |
| 66 | /// @return A <code>PP_Instance</code> internal instance handle. |
| 67 | PP_Instance pp_instance() const { return pp_instance_; } |
| 68 | |
| 69 | private: |
| 70 | PP_Instance pp_instance_; |
| 71 | }; |
| 72 | |
| 73 | } // namespace pp |
| 74 | |
| 75 | #endif // PPAPI_CPP_INSTANCE_HANDLE_H_ |