136 lines
5.4 KiB
C++
136 lines
5.4 KiB
C++
//========= Copyright Valve Corporation, All rights reserved. ============//
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//
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// Purpose:
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//
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// $NoKeywords: $
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//
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//=============================================================================//
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// This makes it easy to dynamically load a shared library and lookup a
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// function in that library.
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//
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// Usage:
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// CDynamicFunction<void (*)(const char *)> MyPuts(libname, "puts");
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// if (MyPuts)
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// MyPuts("Hello world!");
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//
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// Please note that this interface does not distinguish between functions and
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// data. If you look up a global variable in your shared library, or simply
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// mess up the function signature, you'll get a valid pointer and a crash
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// if you call it as a function.
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#ifndef DYNFUNCTION_H
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#define DYNFUNCTION_H
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#pragma once
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#include "tier0/platform.h"
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// The heavy lifting isn't template-specific, so we move it out of the header.
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DLL_EXPORT void *VoidFnPtrLookup_Tier0(const char *libname, const char *fn,
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void *fallback);
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template <class FunctionType>
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class CDynamicFunction {
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public:
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// Construct with a NULL function pointer. You must manually call
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// Lookup() before you can call a dynamic function through this interface.
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CDynamicFunction() : m_pFn(NULL) {}
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// Construct and do a lookup right away. You will need to make sure that
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// the lookup actually succeeded, as (libname) might have failed to load
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// or (fn) might not exist in it.
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CDynamicFunction(const char *libname, const char *fn,
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FunctionType fallback = NULL)
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: m_pFn(NULL) {
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Lookup(libname, fn, fallback);
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}
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// Construct and do a lookup right away. See comments in Lookup() about what
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// (okay) does.
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CDynamicFunction(const char *libname, const char *fn, bool &okay,
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FunctionType fallback = NULL)
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: m_pFn(NULL) {
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Lookup(libname, fn, okay, fallback);
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}
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// Load library if necessary, look up symbol. Returns true and sets
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// m_pFn on successful lookup, returns false otherwise. If the
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// function pointer is already looked up, this return true immediately.
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// Use Reset() first if you want to look up the symbol again.
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// This function will return false immediately unless (okay) is true.
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// This allows you to chain lookups like this:
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// bool okay = true;
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// x.Lookup(lib, "x", okay);
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// y.Lookup(lib, "y", okay);
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// z.Lookup(lib, "z", okay);
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// if (okay) { printf("All functions were loaded successfully!\n"); }
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// If you supply a fallback, it'll be used if the lookup fails (and if
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// non-NULL, means this will always return (okay)).
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bool Lookup(const char *libname, const char *fn, bool &okay,
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FunctionType fallback = NULL) {
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if (!okay)
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return false;
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else if (m_pFn == NULL)
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m_pFn = (FunctionType)VoidFnPtrLookup_Tier0(libname, fn,
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(void *)fallback);
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okay = m_pFn != NULL;
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return okay;
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}
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// Load library if necessary, look up symbol. Returns true and sets
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// m_pFn on successful lookup, returns false otherwise. If the
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// function pointer is already looked up, this return true immediately.
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// Use Reset() first if you want to look up the symbol again.
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// This function will return false immediately unless (okay) is true.
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// If you supply a fallback, it'll be used if the lookup fails (and if
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// non-NULL, means this will always return true).
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bool Lookup(const char *libname, const char *fn,
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FunctionType fallback = NULL) {
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bool okay = true;
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return Lookup(libname, fn, okay, fallback);
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}
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// Invalidates the current lookup. Makes the function pointer NULL. You
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// will need to call Lookup() before you can call a dynamic function
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// through this interface again.
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void Reset() { m_pFn = NULL; }
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// Force this to be a specific function pointer.
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void Force(FunctionType ptr) { m_pFn = ptr; }
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// Retrieve the actual function pointer.
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FunctionType Pointer() const { return m_pFn; }
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operator FunctionType() const { return m_pFn; }
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// Can be used to verify that we have an actual function looked up and
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// ready to call: if (!MyDynFunc) { printf("Function not found!\n"); }
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operator bool() const { return m_pFn != NULL; }
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bool operator!() const { return m_pFn == NULL; }
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protected:
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FunctionType m_pFn;
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};
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// This is the same as CDynamicFunction, but we made the default constructor
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// private, forcing you to do loading/lookup during construction.
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// The usage pattern is to have a list of dynamic functions that are
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// constructed en masse as part of another class's constructor, with the
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// possibility of human error removed (the compiler will complain if you
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// forget to initialize one).
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template <class FunctionType>
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class CDynamicFunctionMustInit : public CDynamicFunction<FunctionType> {
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private: // forbid default constructor.
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CDynamicFunctionMustInit() {}
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public:
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CDynamicFunctionMustInit(const char *libname, const char *fn,
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FunctionType fallback = NULL)
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: CDynamicFunction<FunctionType>(libname, fn, fallback) {}
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CDynamicFunctionMustInit(const char *libname, const char *fn, bool &okay,
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FunctionType fallback = NULL)
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: CDynamicFunction<FunctionType>(libname, fn, okay, fallback) {}
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};
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#endif // DYNFUNCTION_H
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