Revert changes that migrate to thread_local.

iOS 8 does not support `thread_local`, which is still in use.
Another approach will have to be found.

This change is a revert of the following changes:

a3845240 - "Simplify PoolAlloc with use of thread_local."
abf92c80 - "Deprecate InitializeDll functions"
33585c87 - "Limit visibility of symbols for internal libraries"

Issue: #2346

OGLCompilersDLL/InitializeDll.cpp

@@ -32,6 +32,134 @@
 // POSSIBILITY OF SUCH DAMAGE.
 //
 
+#define SH_EXPORTING
+
+#include <cassert>
+
+#include "InitializeDll.h"
+#include "../glslang/Include/InitializeGlobals.h"
+#include "../glslang/Public/ShaderLang.h"
+#include "../glslang/Include/PoolAlloc.h"
+
 namespace glslang {
 
+OS_TLSIndex ThreadInitializeIndex = OS_INVALID_TLS_INDEX;
+
+// Per-process initialization.
+// Needs to be called at least once before parsing, etc. is done.
+// Will also do thread initialization for the calling thread; other
+// threads will need to do that explicitly.
+bool InitProcess()
+{
+    glslang::GetGlobalLock();
+
+    if (ThreadInitializeIndex != OS_INVALID_TLS_INDEX) {
+        //
+        // Function is re-entrant.
+        //
+
+        glslang::ReleaseGlobalLock();
+        return true;
+    }
+
+    ThreadInitializeIndex = OS_AllocTLSIndex();
+
+    if (ThreadInitializeIndex == OS_INVALID_TLS_INDEX) {
+        assert(0 && "InitProcess(): Failed to allocate TLS area for init flag");
+
+        glslang::ReleaseGlobalLock();
+        return false;
+    }
+
+    if (! InitializePoolIndex()) {
+        assert(0 && "InitProcess(): Failed to initialize global pool");
+
+        glslang::ReleaseGlobalLock();
+        return false;
+    }
+
+    if (! InitThread()) {
+        assert(0 && "InitProcess(): Failed to initialize thread");
+
+        glslang::ReleaseGlobalLock();
+        return false;
+    }
+
+    glslang::ReleaseGlobalLock();
+    return true;
+}
+
+// Per-thread scoped initialization.
+// Must be called at least once by each new thread sharing the
+// symbol tables, etc., needed to parse.
+bool InitThread()
+{
+    //
+    // This function is re-entrant
+    //
+    if (ThreadInitializeIndex == OS_INVALID_TLS_INDEX) {
+        assert(0 && "InitThread(): Process hasn't been initalised.");
+        return false;
+    }
+
+    if (OS_GetTLSValue(ThreadInitializeIndex) != 0)
+        return true;
+
+    if (! OS_SetTLSValue(ThreadInitializeIndex, (void *)1)) {
+        assert(0 && "InitThread(): Unable to set init flag.");
+        return false;
+    }
+
+    glslang::SetThreadPoolAllocator(nullptr);
+
+    return true;
+}
+
+// Not necessary to call this: InitThread() is reentrant, and the need
+// to do per thread tear down has been removed.
+//
+// This is kept, with memory management removed, to satisfy any exiting
+// calls to it that rely on it.
+bool DetachThread()
+{
+    bool success = true;
+
+    if (ThreadInitializeIndex == OS_INVALID_TLS_INDEX)
+        return true;
+
+    //
+    // Function is re-entrant and this thread may not have been initialized.
+    //
+    if (OS_GetTLSValue(ThreadInitializeIndex) != 0) {
+        if (!OS_SetTLSValue(ThreadInitializeIndex, (void *)0)) {
+            assert(0 && "DetachThread(): Unable to clear init flag.");
+            success = false;
+        }
+    }
+
+    return success;
+}
+
+// Not necessary to call this: InitProcess() is reentrant.
+//
+// This is kept, with memory management removed, to satisfy any exiting
+// calls to it that rely on it.
+//
+// Users of glslang should call shFinalize() or glslang::FinalizeProcess() for
+// process-scoped memory tear down.
+bool DetachProcess()
+{
+    bool success = true;
+
+    if (ThreadInitializeIndex == OS_INVALID_TLS_INDEX)
+        return true;
+
+    success = DetachThread();
+
+    OS_FreeTLSIndex(ThreadInitializeIndex);
+    ThreadInitializeIndex = OS_INVALID_TLS_INDEX;
+
+    return success;
+}
+
 } // end namespace glslang