curl_version_info: add CURL_VERSION_THREADSAFE_INIT

This flag can be used to make sure that curl_global_init() is
thread-safe.

This can be useful for libraries that can't control what other
dependencies are doing with Curl.

Closes #8680

configure.ac

@@ -4258,6 +4258,23 @@ if test ${ac_cv_sizeof_curl_off_t} -gt 4; then
   fi
 fi
 
+if test "$tst_atomic" = "yes"; then
+  SUPPORT_FEATURES="$SUPPORT_FEATURES threadsafe-init"
+else
+  AC_COMPILE_IFELSE([
+    AC_LANG_PROGRAM([[
+      #include <windows.h>
+    ]],[[
+      #if (WINVER < 0x600) && (_WIN32_WINNT < 0x600)
+      #error
+      #endif
+    ]])
+  ],[
+     SUPPORT_FEATURES="$SUPPORT_FEATURES threadsafe-init"
+  ],[
+  ])
+fi
+
 dnl replace spaces with newlines
 dnl sort the lines
 dnl replace the newlines back to spaces

docs/libcurl/curl_version_info.3

@@ -204,6 +204,9 @@ libcurl was built with support for SSPI. This is only available on Windows and
 makes libcurl use Windows-provided functions for Kerberos, NTLM, SPNEGO and
 Digest authentication. It also allows libcurl to use the current user
 credentials without the app having to pass them on. (Added in 7.13.2)
+.IP CURL_VERSION_THREADSAFE_INIT
+libcurl was built with thread-safety support (Atomic or SRWLOCK) to protect
+curl initialisation. (Added in 7.84.0)
 .IP CURL_VERSION_TLSAUTH_SRP
 libcurl was built with support for TLS-SRP (in one or more of the built-in TLS
 backends). (Added in 7.21.4)

docs/libcurl/symbols-in-versions

@@ -172,6 +172,7 @@ CURL_VERSION_PSL                7.47.0
 CURL_VERSION_SPNEGO             7.10.8
 CURL_VERSION_SSL                7.10
 CURL_VERSION_SSPI               7.13.2
+CURL_VERSION_THREADSAFE_INIT    7.84.0
 CURL_VERSION_TLSAUTH_SRP        7.21.4
 CURL_VERSION_UNICODE            7.72.0
 CURL_VERSION_UNIX_SOCKETS       7.40.0

include/curl/curl.h

@@ -2607,8 +2607,10 @@ CURL_EXTERN void curl_free(void *p);
  *
  * curl_global_init() should be invoked exactly once for each application that
  * uses libcurl and before any call of other libcurl functions.
- *
- * This function is not thread-safe!
+
+ * This function is thread-safe if CURL_VERSION_THREADSAFE_INIT is set in the
+ * curl_version_info_data.features flag (fetch by curl_version_info()).
+
  */
 CURL_EXTERN CURLcode curl_global_init(long flags);
 
@@ -3025,6 +3027,8 @@ typedef struct curl_version_info_data curl_version_info_data;
 #define CURL_VERSION_UNICODE      (1<<27) /* Unicode support on Windows */
 #define CURL_VERSION_HSTS         (1<<28) /* HSTS is supported */
 #define CURL_VERSION_GSASL        (1<<29) /* libgsasl is supported */
+#define CURL_VERSION_THREADSAFE_INIT (1<<30) /* curl_global_init/cleanup() are
+                                                thread-safe */
 
  /*
  * NAME curl_version_info()

lib/version.c

@@ -29,6 +29,7 @@
 #include "vssh/ssh.h"
 #include "quic.h"
 #include "curl_printf.h"
+#include "easy_lock.h"
 
 #ifdef USE_ARES
 #  if defined(CURL_STATICLIB) && !defined(CARES_STATICLIB) &&   \
@@ -450,6 +451,9 @@ static curl_version_info_data version_info = {
 #endif
 #if defined(USE_GSASL)
   | CURL_VERSION_GSASL
+#endif
+#if defined(GLOBAL_INIT_IS_THREADSAFE)
+  | CURL_VERSION_THREADSAFE_INIT
 #endif
   ,
   NULL, /* ssl_version */

packages/OS400/curl.inc.in

@@ -148,6 +148,8 @@
      d                 c                   X'10000000'
      d CURL_VERSION_GSASL...
      d                 c                   X'20000000'
+     d CURL_VERSION_THREADSAFE_INIT...
+     d                 c                   X'40000000'
       *
      d CURL_HTTPPOST_FILENAME...
      d                 c                   X'00000001'

src/tool_help.c

@@ -110,6 +110,7 @@ static const struct feat feats[] = {
   {"alt-svc",        CURL_VERSION_ALTSVC},
   {"HSTS",           CURL_VERSION_HSTS},
   {"gsasl",          CURL_VERSION_GSASL},
+  {"threadsafe-init",CURL_VERSION_THREADSAFE_INIT},
 };
 
 static void print_category(curlhelp_t category)

tests/data/Makefile.inc

@@ -245,4 +245,4 @@ test2200 test2201 test2202 test2203 test2204 test2205 \
 test3000 test3001 test3002 test3003 test3004 test3005 test3006 test3007 \
 test3008 test3009 test3010 test3011 test3012 test3013 test3014 test3015 \
 test3016 test3017 test3018 test3019 test3020 test3021 test3022 test3023 \
-test3024 test3025
+test3024 test3025 test3026

tests/libtest/Makefile.inc

@@ -63,7 +63,7 @@ noinst_PROGRAMS = chkhostname libauthretry libntlmconnect                \
          lib1915 lib1916 lib1917 lib1918 lib1919 \
  lib1933 lib1934 lib1935 lib1936 lib1937 lib1938 lib1939 lib1940 \
  lib1945 lib1946 \
- lib3010 lib3025
+ lib3010 lib3025 lib3026
 
 chkdecimalpoint_SOURCES = chkdecimalpoint.c ../../lib/mprintf.c \
  ../../lib/curl_ctype.c  ../../lib/dynbuf.c ../../lib/strdup.c
@@ -747,3 +747,7 @@ lib3010_CPPFLAGS = $(AM_CPPFLAGS)
 lib3025_SOURCES = lib3025.c $(SUPPORTFILES) $(TESTUTIL) $(WARNLESS)
 lib3025_LDADD = $(TESTUTIL_LIBS)
 lib3025_CPPFLAGS = $(AM_CPPFLAGS)
+
+lib3026_SOURCES = lib3026.c $(SUPPORTFILES) $(TESTUTIL) $(WARNLESS)
+lib3026_LDADD = $(TESTUTIL_LIBS)
+lib3026_CPPFLAGS = $(AM_CPPFLAGS)

tests/libtest/lib3026.c

@@ -0,0 +1,101 @@
+/***************************************************************************
+ *                                  _   _ ____  _
+ *  Project                     ___| | | |  _ \| |
+ *                             / __| | | | |_) | |
+ *                            | (__| |_| |  _ <| |___
+ *                             \___|\___/|_| \_\_____|
+ *
+ * Copyright (C) 1998 - 2022, Daniel Stenberg, <daniel@haxx.se>, et al.
+ *
+ * This software is licensed as described in the file COPYING, which
+ * you should have received as part of this distribution. The terms
+ * are also available at https://curl.se/docs/copyright.html.
+ *
+ * You may opt to use, copy, modify, merge, publish, distribute and/or sell
+ * copies of the Software, and permit persons to whom the Software is
+ * furnished to do so, under the terms of the COPYING file.
+ *
+ * This software is distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY
+ * KIND, either express or implied.
+ *
+ ***************************************************************************/
+#include "test.h"
+
+#include "testutil.h"
+#include "warnless.h"
+
+#ifdef HAVE_PTHREAD_H
+#include <pthread.h>
+#include <unistd.h>
+
+#define NUM_THREADS 1000
+
+static void *run_thread(void *ptr)
+{
+  CURLcode *result = ptr;
+
+  *result = curl_global_init(CURL_GLOBAL_ALL);
+  if(*result == CURLE_OK)
+    curl_global_cleanup();
+
+  return NULL;
+}
+
+int test(char *URL)
+{
+  CURLcode results[NUM_THREADS];
+  pthread_t tids[NUM_THREADS];
+  unsigned tid_count = NUM_THREADS, i;
+  int test_failure = 0;
+  curl_version_info_data *ver;
+  (void) URL;
+
+  ver = curl_version_info(CURLVERSION_NOW);
+  if((ver->features & CURL_VERSION_THREADSAFE_INIT) == 0) {
+    fprintf(stderr, "%s:%d Have pthread but the "
+            "CURL_VERSION_THREADSAFE_INIT feature flag is not set\n",
+            __FILE__, __LINE__);
+    return -1;
+  }
+
+  for(i = 0; i < tid_count; i++) {
+    int res = pthread_create(&tids[i], NULL, run_thread, &results[i]);
+    if(res) {
+      fprintf(stderr, "%s:%d Couldn't create thread, errno %d\n",
+              __FILE__, __LINE__, res);
+      tid_count = i;
+      test_failure = -1;
+      goto cleanup;
+    }
+  }
+
+cleanup:
+  for(i = 0; i < tid_count; i++) {
+    pthread_join(tids[i], NULL);
+    if(results[i] != CURLE_OK) {
+      fprintf(stderr, "%s:%d thread[%u]: curl_global_init() failed,"
+              "with code %d (%s)\n", __FILE__, __LINE__,
+              i, (int) results[i], curl_easy_strerror(results[i]));
+      test_failure = -1;
+    }
+  }
+
+  return test_failure;
+}
+
+#else /* without pthread, this test doesn't work */
+int test(char *URL)
+{
+  curl_version_info_data *ver;
+  (void)URL;
+
+  ver = curl_version_info(CURLVERSION_NOW);
+  if((ver->features & CURL_VERSION_THREADSAFE_INIT) != 0) {
+    fprintf(stderr, "%s:%d No pthread but the "
+            "CURL_VERSION_THREADSAFE_INIT feature flag is set\n",
+            __FILE__, __LINE__);
+    return -1;
+  }
+  return 0;
+}
+#endif