Compiling "threaded-ssl.c" with PThreads4W

[gvanem]

I did this

Compiling docs/examples/threaded-ssl.c using POSIX threads for Windows or
PThreads4W, gives me this compile error (from clang-cl):

threaded-ssl.c(68,24): error: operand of type 'pthread_t' (aka '__ptw32_handle_t') 
where arithmetic or pointer type is required
   68 |   ret = (unsigned long)pthread_self();
      |                        ^~~~~~~~~~~~~~

This is caused by pthread_t which is a structure on Pthreads4W.

But with this patch, it compiles:

--- a/docs/examples/threaded-ssl.c 2023-01-05 13:01:10
+++ b/docs/examples/threaded-ssl.c 2024-05-04 09:18:18
@@ -65,7 +65,11 @@
 {
   unsigned long ret;

+#if defined(__PTW32_H)   /* Using 'Pthreads for Windows' */
+  ret = *(unsigned long*) (pthread_self().p);
+#else
   ret = (unsigned long)pthread_self();
+#endif
   return ret;
 }

And the program works.

I expected the following

A successful compile.

curl/libcurl version

WARNING: this libcurl is Debug-enabled, do not use in production

curl 8.8.0-DEV (x86_64-pc-win32) libcurl/8.8.0-DEV (mbedTLS/3.6.0) (OpenSSL/3.3.0) Schannel (BearSSL) 
(rustls-ffi/0.13.0/rustls/0.23.4) zlib/1.3 brotli/1.1.0 zstd/1.5.5 c-ares/1.28.1 WinIDN libssh2/1.10.1_DEV nghttp2/1.61.0
Release-Date: [unreleased]
Protocols: dict file ftp ftps gopher gophers http https imap imaps ipfs ipns ldap ldaps mqtt pop3 pop3s rtsp scp sftp 
smb smbs smtp smtps telnet tftp ws wss
Features: alt-svc AsynchDNS brotli Debug HSTS HTTP2 HTTPS-proxy IDN IPv6 Kerberos Largefile libz MultiSSL 
NTLM SPNEGO SSL SSPI threadsafe TLS-SRP TrackMemory UnixSockets zstd

operating system

Win-10.

[bagder]

I think that proposal introduces a hideous piece of code I rather not have in an example we provide showing off libcurl with.

[jay]

I think that proposal introduces a hideous piece of code I rather not have in an example we provide showing off libcurl with.

Seems harsh. POSIX allows pthread_t to be opaque so the way we cast it to long for thread id will not always work, like for PThreads4W as we can see here. How about a comment that explains this situation:

diff --git a/docs/examples/threaded-ssl.c b/docs/examples/threaded-ssl.c
index f58e447..4feea80 100644
--- a/docs/examples/threaded-ssl.c
+++ b/docs/examples/threaded-ssl.c
@@ -65,6 +65,8 @@ static unsigned long thread_id(void)
 {
   unsigned long ret;

+  /* How to obtain the thread ID will vary depending on the pthreads library
+     you are using. This example assumes pthread_self returns the ID. */
   ret = (unsigned long)pthread_self();
   return ret;
 }

[gvanem]

How about a comment that explains this situation:

A comment wont fix the compile error.

[jay]

A comment wont fix the compile error.

Yeah but it is an example, it's not meant to address all cases. It is not correct to cast pthread_self() to unsigned long. It is not correct to cast pthread_self().p to unsigned long either.