Bump version to 0.3.0rc7 and relax backend version requirement (#552)

### Summary:

Update the Neuropod version to `0.3.0rc7`.

This PR also allows Neuropod `0.3.0rc7` to use backends from `0.3.0rc6`. This is a temporary workaround to avoid having to reinstall backends whenever upgrading the main library. This will be improved once we have a long term release/ABI compatibility strategy (along with an ability to test and enforce it in CI).

### Test Plan:

CI + Local tests by @qiyanz to check backend compatibility

Author: VivekPanyam

docs/installing.md

@@ -42,7 +42,7 @@ sudo mkdir -p "$NEUROPOD_BASE_DIR"
 # Find URLs of backends you want to install from the releases page (https://github.com/uber/neuropod/releases) and install them
 # by untarring them in your NEUROPOD_BASE_DIR directory.
 # For example, to install a GPU enabled Torch 1.7 backend for CUDA 10.1, run
-curl -L https://github.com/uber/neuropod/releases/download/v0.3.0-rc6/libneuropod-gpu-cuda-10.1-linux-v0.3.0-rc6-torchscript-1.7.0-backend.tar.gz | sudo tar -xz -C "$NEUROPOD_BASE_DIR"
+curl -L https://github.com/uber/neuropod/releases/download/v0.3.0-rc7/libneuropod-gpu-cuda-10.1-linux-v0.3.0-rc7-torchscript-1.7.0-backend.tar.gz | sudo tar -xz -C "$NEUROPOD_BASE_DIR"
 ```
 
 Multiple backends can be installed for a given framework and Neuropod will select the correct one when loading a model.

source/bazel/version.bzl

@@ -1 +1 @@
-NEUROPOD_VERSION = "0.3.0rc6"
+NEUROPOD_VERSION = "0.3.0rc7"

source/neuropod/internal/backend_registration.cc

@@ -53,10 +53,8 @@ void init_registrar_if_needed()
     });
 }
 
-std::vector<BackendLoadSpec> get_default_backend_map()
+void populate_default_backend_map(const std::string &neuropod_version, std::vector<BackendLoadSpec> &out)
 {
-    std::vector<BackendLoadSpec> out;
-
     // A structure to store some basic info about frameworks we support
     struct FrameworkInfo
     {
@@ -113,7 +111,7 @@ std::vector<BackendLoadSpec> get_default_backend_map()
                         //  "/usr/local/lib/neuropod/0.2.0/backends/torchscript_1.4.0/libneuropod_torchscript_backend.so"
                         // Ex:
                         //  "/usr/local/lib/neuropod/0.2.0/backends/torchscript_1.4.0_gpu/libneuropod_torchscript_backend.so"
-                        item.path = neuropod_base_dir + ("/" NEUROPOD_VERSION "/backends/") + framework.type + "_" +
+                        item.path = neuropod_base_dir + ("/" + neuropod_version + "/backends/") + framework.type + "_" +
                                     version + (is_gpu ? "_gpu" : "") + "/" + framework.soname;
                     }
                     else
@@ -126,6 +124,25 @@ std::vector<BackendLoadSpec> get_default_backend_map()
             }
         }
     }
+}
+
+std::vector<BackendLoadSpec> get_default_backend_map()
+{
+    // Reverse priority order (highest priority at the end of the vector)
+    std::vector<BackendLoadSpec> out;
+
+    // TODO: improve this once we have a long term strategy on ABI compatibility
+    //
+    // If we decide not to break ABI compatibility within a given major version,
+    // maybe we just filter the folders in NEUROPOD_BASE_DIR instead of listing
+    // all possible versions
+    std::vector<std::string> supported_versions = {"0.3.0rc6", "0.3.0rc7"};
+    assert(supported_versions.back() == NEUROPOD_VERSION);
+
+    for (const auto &version : supported_versions)
+    {
+        populate_default_backend_map(version, out);
+    }
 
     return out;
 }

source/neuropod/version.hh

@@ -32,13 +32,13 @@ namespace neuropod
 
 // These are allowed to be 4 bits each
 #define NEUROPOD_RELEASE_LEVEL NEUROPOD_RELEASE_LEVEL_RELEASE_CANDIDATE
-#define NEUROPOD_RELEASE_SERIAL 6
+#define NEUROPOD_RELEASE_SERIAL 7
 
 static_assert(NEUROPOD_RELEASE_LEVEL < 16, "NEUROPOD_RELEASE_LEVEL must be in the range 0 to 15 (4 bits)");
 static_assert(NEUROPOD_RELEASE_SERIAL < 16, "NEUROPOD_RELEASE_SERIAL must be in the range 0 to 15 (4 bits)");
 
 // The version as a string
-#define NEUROPOD_VERSION "0.3.0rc6"
+#define NEUROPOD_VERSION "0.3.0rc7"
 
 // Version as a single 4-byte hex number, e.g. 0x010502B2 == 1.5.2b2.
 // Use this for numeric comparisons

source/python/setup.py

@@ -19,7 +19,7 @@ def has_ext_modules(foo):
 
 setup(
     name="neuropod",
-    version="0.3.0rc6",
+    version="0.3.0rc7",
     install_requires=REQUIRED_PACKAGES,
     packages=find_packages(),
     package_data={