issue-610: introduced TCMallocGetenvSafe

This is version of GetenvBeforeMain that's available to C code.

Makefile.am

@@ -192,6 +192,7 @@ liblogging_la_SOURCES = src/base/logging.cc \
                         $(LOGGING_INCLUDES)
 
 SYSINFO_INCLUDES = src/base/sysinfo.h \
+                   src/getenv_safe.h \
                    src/base/logging.h \
                    src/base/commandlineflags.h \
                    src/base/cycleclock.h \

src/base/sysinfo.cc

@@ -167,6 +167,12 @@ const char* GetenvBeforeMain(const char* name) {
   return NULL;                   // env var never found
 }
 
+extern "C" {
+  const char* TCMallocGetenvSafe(const char* name) {
+    return GetenvBeforeMain(name);
+  }
+}
+
 // This takes as an argument an environment-variable name (like
 // CPUPROFILE) whose value is supposed to be a file-path, and sets
 // path to that path, and returns true.  If the env var doesn't exist,

src/getenv_safe.h

@@ -0,0 +1,63 @@
+/* -*- Mode: C++; c-basic-offset: 2; indent-tabs-mode: nil -*-
+ * Copyright (c) 2014, gperftools Contributors
+ * All rights reserved.
+ * 
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are
+ * met:
+ * 
+ *     * Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ *     * Redistributions in binary form must reproduce the above
+ * copyright notice, this list of conditions and the following disclaimer
+ * in the documentation and/or other materials provided with the
+ * distribution.
+ *     * Neither the name of Google Inc. nor the names of its
+ * contributors may be used to endorse or promote products derived from
+ * this software without specific prior written permission.
+ * 
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+ * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+ * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+ * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#ifndef GETENV_SAFE_H
+#define GETENV_SAFE_H
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+/* 
+ * This getenv function is safe to call before the C runtime is initialized.
+ * On Windows, it utilizes GetEnvironmentVariable() and on unix it uses
+ * /proc/self/environ instead calling getenv().  It's intended to be used in
+ * routines that run before main(), when the state required for getenv() may
+ * not be set up yet.  In particular, errno isn't set up until relatively late
+ * (after the pthreads library has a chance to make it threadsafe), and
+ * getenv() doesn't work until then.
+ * On some platforms, this call will utilize the same, static buffer for
+ * repeated GetenvBeforeMain() calls. Callers should not expect pointers from
+ * this routine to be long lived.
+ * Note that on unix, /proc only has the environment at the time the
+ * application was started, so this routine ignores setenv() calls/etc.  Also
+ * note it only reads the first 16K of the environment.
+ * 
+ * NOTE: this is version of GetenvBeforeMain that's usable from
+ * C. Implementation is in sysinfo.cc
+ */
+const char* TCMallocGetenvSafe(const char* name);
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif