Dynamic Linker

# Dynamic Linker

The names in `Base.Libdl` are not exported and need to be called e.g. as `Libdl.dlopen()`.

`Base.Libdl.dlopen` — Function.

    dlopen(libfile::AbstractString [, flags::Integer])

Load a shared library, returning an opaque handle.

The extension given by the constant `dlext` (`.so`, `.dll`, or `.dylib`) can be omitted from the `libfile` string, as it is automatically appended if needed. If `libfile` is not an absolute path name, then the paths in the array `DL_LOAD_PATH` are searched for `libfile`, followed by the system load path.

The optional flags argument is a bitwise-or of zero or more of `RTLD_LOCAL`, `RTLD_GLOBAL`, `RTLD_LAZY`, `RTLD_NOW`, `RTLD_NODELETE`, `RTLD_NOLOAD`, `RTLD_DEEPBIND`, and `RTLD_FIRST`. These are converted to the corresponding flags of the POSIX (and/or GNU libc and/or MacOS) dlopen command, if possible, or are ignored if the specified functionality is not available on the current platform. The default flags are platform specific. On MacOS the default `dlopen` flags are `RTLD_LAZY|RTLD_DEEPBIND|RTLD_GLOBAL` while on other platforms the defaults are `RTLD_LAZY|RTLD_DEEPBIND|RTLD_LOCAL`. An important usage of these flags is to specify non default behavior for when the dynamic library loader binds library references to exported symbols and if the bound references are put into process local or global scope. For instance `RTLD_LAZY|RTLD_DEEPBIND|RTLD_GLOBAL` allows the library's symbols to be available for usage in other shared libraries, addressing situations where there are dependencies between shared libraries.

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`Base.Libdl.dlopen_e` — Function.

    dlopen_e(libfile::AbstractString [, flags::Integer])

Similar to `dlopen`, except returns a `NULL` pointer instead of raising errors.

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`Base.Libdl.RTLD_NOW` — Constant.

    RTLD_DEEPBIND
    RTLD_FIRST
    RTLD_GLOBAL
    RTLD_LAZY
    RTLD_LOCAL
    RTLD_NODELETE
    RTLD_NOLOAD
    RTLD_NOW

Enum constant for `dlopen`. See your platform man page for details, if applicable.

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`Base.Libdl.dlsym` — Function.

    dlsym(handle, sym)

Look up a symbol from a shared library handle, return callable function pointer on success.

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`Base.Libdl.dlsym_e` — Function.

    dlsym_e(handle, sym)

Look up a symbol from a shared library handle, silently return `NULL` pointer on lookup failure.

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`Base.Libdl.dlclose` — Function.

    dlclose(handle)

Close shared library referenced by handle.

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`Base.Libdl.dlext` — Constant.

    dlext

File extension for dynamic libraries (e.g. dll, dylib, so) on the current platform.

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`Base.Libdl.find_library` — Function.

    find_library(names, locations)

Searches for the first library in `names` in the paths in the `locations` list, `DL_LOAD_PATH`, or system library paths (in that order) which can successfully be dlopen'd. On success, the return value will be one of the names (potentially prefixed by one of the paths in locations). This string can be assigned to a `global const` and used as the library name in future `ccall`'s. On failure, it returns the empty string.

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`Base.Libdl.DL_LOAD_PATH` — Constant.

    DL_LOAD_PATH

When calling `dlopen`, the paths in this list will be searched first, in order, before searching the system locations for a valid library handle.

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