curl_threads: fix MSVC compiler warning

[MarcelRaad]

Use LongToHandle to convert from long to HANDLE in the Win32
implementation.
This should fix the following warning when compiling with
MSVC 11 (2012) in 64-bit mode visible in #1711:

lib\curl_threads.c(113): warning C4306: 'type cast' : conversion from 'long' to 'HANDLE' of greater size

LongToHandle is available in the February 2003 Platform SDK, so I think we should be safe. Alternatively, INVALID_HANDLE_VALUE could be used (the documented value in the _beginthreadex documentation is -1L, though).

[coveralls]

Coverage increased (+0.09%) to 75.355% when pulling 06a57ae42b71eee298c66e301b7b228161de3ae8 on MarcelRaad:msvc11_c4306 into 53d137d on curl:master.

[coveralls]

Coverage increased (+0.04%) to 75.321% when pulling 12b4fb7 on MarcelRaad:msvc11_c4306 into 821a085 on curl:master.

[jay]

I can't reproduce this warning in VS 2010 in a test project at W4 or 2015 in curl project at W4. original mingw only defines LongToHandle if win64 so that will need to be addressed. from what i understand beginthreadex can return 0 or -1 uintptr_t on error (0 but it contradicts because -1 in some versions if startaddress is null). CreateThread can return 0 HANDLE on error. do you get a warning if you drop the L for example if((t == 0) || (t == (curl_thread_t)(uintptr_t)-1)) {

[jay]

I tried in VS2010 curl project at W4 and I can reproduce it there, this fixes it:

diff --git a/lib/curl_threads.c b/lib/curl_threads.c
index 1989710..53fed9c 100644
--- a/lib/curl_threads.c
+++ b/lib/curl_threads.c
@@ -110,7 +110,7 @@ curl_thread_t Curl_thread_create(unsigned int (CURL_STDCALL *func) (void *),
 #else
   t = (curl_thread_t)_beginthreadex(NULL, 0, func, arg, 0, NULL);
 #endif
-  if((t == 0) || (t == (curl_thread_t)-1L)) {
+  if((t == 0) || (t == (curl_thread_t)(uintptr_t)-1)) {
 #ifdef _WIN32_WCE
     DWORD gle = GetLastError();
     errno = ((gle == ERROR_ACCESS_DENIED ||

[MarcelRaad]

Thanks @jay! That's strange as original MinGW cannot even compile for Win64.
Unfortunately older MSVC versions don't have uintptr_t, IIRC it was introduced in VS 2003. Maybe LONG_PTR can be used instead, that would have been my preferred alternative, but I decided for LongToHandle as they were introduced in the same SDK version. I'll check tomorrow.

[MarcelRaad]

@jay I can compile successfully with MinGW and --enable-threaded-resolver --disable-pthreads. It looks like LongToHandle is only defined when not compiling for Win64, so it should be OK. I had to look twice too though, the code in basetsd.h looks like this:

#if defined(_WIN64)
#define __int3264   __int64
#define ADDRESS_TAG_BIT 0x40000000000UI64
#else /*  !_WIN64 */
#define __int3264   __int32
#define ADDRESS_TAG_BIT 0x80000000UL
#define HandleToUlong( h ) ((ULONG)(ULONG_PTR)(h) )
#define HandleToLong( h ) ((LONG)(LONG_PTR) (h) )
#define LongToHandle( h) ((HANDLE)(LONG_PTR) (h))
#define PtrToUlong( p ) ((ULONG)(ULONG_PTR) (p) )
#define PtrToLong( p ) ((LONG)(LONG_PTR) (p) )
#define PtrToUint( p ) ((UINT)(UINT_PTR) (p) )
#define PtrToInt( p ) ((INT)(INT_PTR) (p) )
#define PtrToUshort( p ) ((unsigned short)(ULONG_PTR)(p) )
#define PtrToShort( p ) ((short)(LONG_PTR)(p) )
#define IntToPtr( i )    ((VOID*)(INT_PTR)((int)i))
#define UIntToPtr( ui )  ((VOID*)(UINT_PTR)((unsigned int)ui))
#define LongToPtr( l )   ((VOID*)(LONG_PTR)((long)l))
#define ULongToPtr( ul )  ((VOID*)(ULONG_PTR)((unsigned long)ul))
#endif /* !_WIN64 */

[jay]

It looks like LongToHandle is only defined when not compiling for Win64, so it should be OK. I had to look twice too though, the code in basetsd.h looks like this:

You're right, I had misinterpreted that, thanks for following up.