pgpl/tests/clap/entry.h

#pragma once

#include "version.h"
#include "private/macros.h"

#ifdef __cplusplus
extern "C" {
#endif

// This interface is the entry point of the dynamic library.
//
// CLAP plugins standard search path:
//
// Linux
//   - ~/.clap
//   - /usr/lib/clap
//
// Windows
//   - %COMMONPROGRAMFILES%\CLAP
//   - %LOCALAPPDATA%\Programs\Common\CLAP
//
// MacOS
//   - /Library/Audio/Plug-Ins/CLAP
//   - ~/Library/Audio/Plug-Ins/CLAP
//
// In addition to the OS-specific default locations above, a CLAP host must query the environment
// for a CLAP_PATH variable, which is a list of directories formatted in the same manner as the host
// OS binary search path (PATH on Unix, separated by `:` and Path on Windows, separated by ';', as
// of this writing).
//
// Each directory should be recursively searched for files and/or bundles as appropriate in your OS
// ending with the extension `.clap`.
//
// init and deinit in most cases are called once, in a matched pair, when the dso is loaded / unloaded.
// In some rare situations it may be called multiple times in a process, so the functions must be defensive,
// mutex locking and counting calls if undertaking non trivial non idempotent actions.
//
// Rationale:
//
//    The intent of the init() and deinit() functions is to provide a "normal" initialization patterh
//    which occurs when the shared object is loaded or unloaded. As such, hosts will call each once and
//    in matched pairs. In CLAP specifications prior to 1.2.0, this single-call was documented as a
//    requirement.
//
//    We realized, though, that this is not a requirement hosts can meet. If hosts load a plugin
//    which itself wraps another CLAP for instance, while also loading that same clap in its memory
//    space, both the host and the wrapper will call init() and deinit() and have no means to communicate
//    the state.
//
//    With CLAP 1.2.0 and beyond we are changing the spec to indicate that a host should make an
//    absolute best effort to call init() and deinit() once, and always in matched pairs (for every
//    init() which returns true, one deinit() should be called).
//
//    This takes the de-facto burden on plugin writers to deal with multiple calls into a hard requirement.
//
//    Most init() / deinit() pairs we have seen are the relatively trivial {return true;} and {}. But
//    if your init() function does non-trivial one time work, the plugin author must maintain a counter
//    and must manage a mutex lock. The most obvious implementation will maintain a static counter and a
//    global mutex, increment the counter on each init, decrement it on each deinit, and only undertake
//    the init or deinit action when the counter is zero.
typedef struct clap_plugin_entry {
   clap_version_t clap_version; // initialized to CLAP_VERSION

   // Initializes the DSO.
   //
   // This function must be called first, before any-other CLAP-related function or symbol from this
   // DSO.
   //
   // It also must only be called once, until a later call to deinit() is made, after which init()
   // can be called once more to re-initialize the DSO.
   // This enables hosts to e.g. quickly load and unload a DSO for scanning its plugins, and then
   // load it again later to actually use the plugins if needed.
   //
   // As stated above, even though hosts are forbidden to do so directly, multiple calls before any
   // deinit() call may still happen. Implementations *should* take this into account, and *must*
   // do so as of CLAP 1.2.0.
   //
   // It should be as fast as possible, in order to perform a very quick scan of the plugin
   // descriptors.
   //
   // It is forbidden to display graphical user interfaces in this call.
   // It is forbidden to perform any user interaction in this call.
   //
   // If the initialization depends upon expensive computation, maybe try to do them ahead of time
   // and cache the result.
   //
   // Returns true on success. If init() returns false, then the DSO must be considered
   // uninitialized, and the host must not call deinit() nor any other CLAP-related symbols from the
   // DSO.
   // This function also returns true in the case where the DSO is already initialized, and no
   // actual initialization work is done in this call, as explain above.
   //
   // plugin_path is the path to the DSO (Linux, Windows), or the bundle (macOS).
   //
   // This function may be called on any thread, including a different one from the one a later call
   // to deinit() (or a later init()) can be made.
   // However, it is forbidden to call this function simultaneously from multiple threads.
   // It is also forbidden to call it simultaneously with *any* other CLAP-related symbols from the
   // DSO, including (but not limited to) deinit().
   bool(CLAP_ABI *init)(const char *plugin_path);

   // De-initializes the DSO, freeing any resources allocated or initialized by init().
   //
   // After this function is called, no more calls into the DSO must be made, except calling init()
   // again to re-initialize the DSO.
   // This means that after deinit() is called, the DSO can be considered to be in the same state
   // as if init() was never called at all yet, enabling it to be re-initialized as needed.
   //
   // As stated above, even though hosts are forbidden to do so directly, multiple calls before any
   // new init() call may still happen. Implementations *should* take this into account, and *must*
   // do so as of CLAP 1.2.0.
   //
   // Just like init(), this function may be called on any thread, including a different one from
   // the one init() was called from, or from the one a later init() call can be made.
   // However, it is forbidden to call this function simultaneously from multiple threads.
   // It is also forbidden to call it simultaneously with *any* other CLAP-related symbols from the
   // DSO, including (but not limited to) deinit().
   void(CLAP_ABI *deinit)(void);

   // Get the pointer to a factory. See factory/plugin-factory.h for an example.
   //
   // Returns null if the factory is not provided.
   // The returned pointer must *not* be freed by the caller.
   //
   // Unlike init() and deinit(), this function can be called simultaneously by multiple threads.
   //
   // [thread-safe]
   const void *(CLAP_ABI *get_factory)(const char *factory_id);
} clap_plugin_entry_t;

/* Entry point */
CLAP_EXPORT extern const clap_plugin_entry_t clap_entry;

#ifdef __cplusplus
}
#endif