diff --git a/include/clap/entry.h b/include/clap/entry.h index c1f9d9c3..877dc941 100644 --- a/include/clap/entry.h +++ b/include/clap/entry.h @@ -31,34 +31,109 @@ extern "C" { // Each directory should be recursively searched for files and/or bundles as appropriate in your OS // ending with the extension `.clap`. // -// Every method must be thread-safe. +// As detailed in the respective functions' documentations below, the host is forbidden from calling +// either init() or deinit() multiple times, without calling the other first. This is to enforce +// a "normal" initialization pattern, where one can't construct or destroy an object multiple times. +// +// However, there are a few cases where the host may not be able to reliably prevent this from +// happening, such as when multiple, separate hosts co-exist within the same address space (e.g. +// Meta-Plugins, plugins that can host other plugins inside them). It may also happen when a VST +// compatibility layer is used to wrap a CLAP plugin, for instance. +// +// In those cases, the init() and deinit() pair of functions can happen to be called multiple times, +// either in a row or even simultaneously, from different threads, by multiple non-synchronized +// hosts, or by a single host that is presented multiple interfaces to a same DSO. This can happen +// even though this is forbidden behavior from the host by this specification, and despite a +// compliant host's best efforts. +// +// Despite those issues, hosts *must* ensure that each successful call to init() is only followed by +// a single call to deinit() at most. As long as a single successful init() call did not have its +// matching deinit() called, the DSO *must* remain in a fully operational state, as if deinit() had +// not yet been called. +// +// Therefore, init() and deinit() functions *should* be implemented in a way that allows for init() +// to be called any number of times in a row (possibly simultaneously, from multiple threads), and +// for deinit() to be called at most that same number of times (also simultaneously, from multiple, +// possibly different threads from the init() called). As of CLAP 1.11, this *must* be the case for +// all plugin implementations. +// +// This is already trivially the case if there is no (de)initialization work in the entry at all, +// or if the initialization work is thread safe and idempotent, and there is no de-initialization +// work to be done. Those implementations already are and remain valid, and require no additional +// consideration. +// +// If that is not the case, then using a global, refcount-like locked initialization counter can be +// used to keep track of init() and deinit() calls. Then the initialization work can be done only +// when the counter goes from 0 to 1 in init(), and de-initialization can be done when the counter +// goes to 0 in deinit(). Any subsequent calls to init() and deinit() can just increase or decrease +// the counter, respectively. typedef struct clap_plugin_entry { clap_version_t clap_version; // initialized to CLAP_VERSION - // This function must be called first, and can only be called once. + // 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 1.11. // // 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 interface in this call. - // It is forbidden to perform user interaction in this call. + // 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. // - // If init() returns false, then the host must not call deinit() nor any other clap - // related symbols from the DSO. + // 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); - // No more calls into the DSO must be made after calling deinit(). + // 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 1.11. + // + // 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;