Lock around encrypted I/Ocmn/lock-io

OpenSSL and often whatever libssh2 is using require their own set-up for
concurrent operations to be safe. This means that by default, using both
of these libraries in a threaded context is unsafe.

Lock by default, and allow the user to tell us that they've set up
threading for the underlying libraries.

2 files changed, 45 insertions, 0 deletions

diff --git a/include/git2/sys/libssh2.h b/include/git2/sys/libssh2.h
new file mode 100644
index 000000000..ca1dec9fb
--- /dev/null
+++ b/include/git2/sys/libssh2.h
@@ -0,0 +1,29 @@
+/*
+ * Copyright (C) the libgit2 contributors. All rights reserved.
+ *
+ * This file is part of libgit2, distributed under the GNU GPL v2 with
+ * a Linking Exception. For full terms see the included COPYING file.
+ */
+#ifndef INCLUDE_git_libssh2_h__
+#define INCLUDE_git_libssh2_h__
+
+#include "git2/common.h"
+
+GIT_BEGIN_DECL
+
+/**
+ * Mark the libssh2 code as thread-safe
+ *
+ * By default we take a lock around libssh2 operations, as the
+ * thread-safety depends on the caller setting up the threading for
+ * the crytographic library it uses. If you have set up its threading,
+ * you may call this function to disable the lock, which would enable
+ * concurrent work.
+ *
+ * These locks are only used if the library was built with threading
+ * support.
+ */
+GIT_EXTERN(void) git_libssh2_set_threadsafe(void);
+
+GIT_END_DECL
+#endif
diff --git a/include/git2/sys/openssl.h b/include/git2/sys/openssl.h
index b41c55c6d..5a5fc8f03 100644
--- a/include/git2/sys/openssl.h
+++ b/include/git2/sys/openssl.h
@@ -28,11 +28,27 @@ GIT_BEGIN_DECL
  * likely sets up locking. You should very strongly prefer that over
  * this function.
  *
+ * This calls `git_openssl_set_threadsafe()` enabling concurrent
+ * OpenSSL operations.
+ *
  * @return 0 on success, -1 if there are errors or if libgit2 was not
  * built with OpenSSL and threading support.
  */
 GIT_EXTERN(int) git_openssl_set_locking(void);
 
+/**
+ * Mark the OpenSSL code as thread-safe
+ *
+ * By default we take a lock around OpenSSL operations. If you have
+ * set up OpenSSL threading in your application, you may call this
+ * function to avoid taking these locks, which would enable concurrent
+ * work.
+ *
+ * These locks are only used if the library was built with threading
+ * support.
+ */
+GIT_EXTERN(void) git_openssl_set_threadsafe(void);
+
 GIT_END_DECL
 #endif