We currently have an explicit callchain of all the initialization callbacks in our `init_common` function. This is perfectly fine, but requires us to manually keep track of how many shutdown callbacks there may be installed: to avoid allocations before libgit2 is fully initialized, we assume that every initializer may register at most one shutdown function. These shutdown functions are stored in a static array of size `MAX_SHUTDOWN_CB`, which then needs to be updated manually whenever a new initializer function is being added. The situation can be easily fixed: convert the callchain of init functions into an array and iterate over it to initialize all subsystems. This allows us to define the `git__shutdown_callbacks` array with the same size as the initializer array and rids us of the need to always update `MAX_SHUTDOWN_CB`.
Update the new stream registration API to be `git_stream_register` which takes a registration structure and a TLS boolean. This allows callers to register non-TLS streams as well as TLS streams. Provide `git_stream_register_tls` that takes just the init callback for backward compatibliity.
We previously used cURL to support HTTP proxies. Now that we've added this support natively, we can remove the curl dependency.
Introduce `git_tls_stream_wrap` which will take an existing `stream` with an already connected socket and begin speaking TLS on top of it. This is useful if you've built a connection to a proxy server and you wish to begin CONNECT over it to tunnel a TLS connection. Also update the pluggable TLS stream layer so that it can accept a registration structure that provides an `init` and `wrap` function, instead of a single initialization function.
Currently, our memory allocators are being redirected to the correct implementation at compile time by simply using macros. In order to make them swappable at runtime, this commit reshuffles that by instead making use of a global "git_allocator" structure, whose pointers are set up to reference the allocator functions. Like this, it becomes easy to swap out allocators by simply setting these function pointers. In order to initialize a "git_allocator", our provided allocators "stdalloc" and "crtdbg" both provide an init function. This is being called to initialize a passed in allocator struct and set up its members correctly. No support is yet included to enable users of libgit2 to switch out the memory allocator at a global level.
global: adjust init count under lock
Our global initialization functions `git_libgit2_init()` and
`git_libgit2_shutdown()` both adjust a global init counter to determine
whether we are the first respectively last user of libgit2. On
Unix-systems do not do so under lock, though, which opens the
possibility of a race between these two functions:
Thread 1 Thread 2
git__n_inits = 0;
git_libgit2_init();
git_atomic_inc(&git__n_inits);
/* git__n_inits == 1 */
git_libgit2_shutdown();
if (git_atomic_dec(&git__n_inits) != 0)
/* git__n_inits == 0, no early exit here */
pthread_mutex_lock(&_init_mutex);
shutdown_common();
pthread_mutex_unlock(&_init_mutex);
pthread_mutex_lock(&_init_mutex);
init_once();
pthread_mutex_unlock(&_init_mutex);
So we can end up in a situation where we try to shutdown shared data
structures before they have been initialized.
Fix the race by always locking `_init_mutex` before incrementing or
decrementing `git__n_inits`.
Our curl-based streams make use of the easy curl interface. This interface automatically initializes and de-initializes the global curl state by calling out to `curl_global_init` and `curl_global_cleanup`. Thus, all global state will be repeatedly re-initialized when creating multiple curl streams in succession. Despite being inefficient, this is not thread-safe due to `curl_global_init` being not thread-safe itself. Thus a multi-threaded programing handling multiple curl streams at the same time is inherently racy. Fix the issue by globally initializing and cleaning up curl's state.