[llvm] [llvm-exegesis] Add thread IDs to subprocess memory names (PR #84451)

[Aiden Grossman via llvm-commits]

https://github.com/boomanaiden154 created https://github.com/llvm/llvm-project/pull/84451

This patch adds the thread ID to the subprocess memory shared memory names. This avoids conflicts for downstream consumers that might want to consume llvm-exegesis across multiple threads, which would otherwise run into conflicts due to the same PID running multiple instances.

>From edd2faabd6639ac44f1a0edc10deb3aed63b3e11 Mon Sep 17 00:00:00 2001
From: Aiden Grossman <agrossman154 at yahoo.com>
Date: Fri, 8 Mar 2024 02:02:52 -0800
Subject: [PATCH] [llvm-exegesis] Add thread IDs to subprocess memory names

This patch adds the thread ID to the subprocess memory shared memory
names. This avoids conflicts for downstream consumers that might want to
consume llvm-exegesis across multiple threads, which would otherwise run
into conflicts due to the same PID running multiple instances.
---
 .../llvm-exegesis/lib/SubprocessMemory.cpp      | 17 ++++++++++++++---
 .../llvm-exegesis/X86/SubprocessMemoryTest.cpp  |  5 ++++-
 2 files changed, 18 insertions(+), 4 deletions(-)

diff --git a/llvm/tools/llvm-exegesis/lib/SubprocessMemory.cpp b/llvm/tools/llvm-exegesis/lib/SubprocessMemory.cpp
index a49fa077257d00..28dc4488a2a004 100644
--- a/llvm/tools/llvm-exegesis/lib/SubprocessMemory.cpp
+++ b/llvm/tools/llvm-exegesis/lib/SubprocessMemory.cpp
@@ -14,6 +14,7 @@
 #ifdef __linux__
 #include <fcntl.h>
 #include <sys/mman.h>
+#include <sys/syscall.h>
 #include <unistd.h>
 #endif
 
@@ -22,12 +23,21 @@ namespace exegesis {
 
 #if defined(__linux__) && !defined(__ANDROID__)
 
+long getCurrentTID() {
+  // We're using the raw syscall here rather than the gettid() function provided
+  // by most libcs for compatibility as gettid() was only added to glibc in
+  // version 2.30.
+  return syscall(SYS_gettid);
+}
+
 Error SubprocessMemory::initializeSubprocessMemory(pid_t ProcessID) {
   // Add the PID to the shared memory name so that if we're running multiple
   // processes at the same time, they won't interfere with each other.
   // This comes up particularly often when running the exegesis tests with
-  // llvm-lit
-  std::string AuxiliaryMemoryName = "/auxmem" + std::to_string(ProcessID);
+  // llvm-lit. Additionally add the TID so that downstream consumers
+  // using multiple threads don't run into conflicts.
+  std::string AuxiliaryMemoryName = "/" + std::to_string(getCurrentTID()) +
+                                    "auxmem" + std::to_string(ProcessID);
   int AuxiliaryMemoryFD = shm_open(AuxiliaryMemoryName.c_str(),
                                    O_RDWR | O_CREAT, S_IRUSR | S_IWUSR);
   if (AuxiliaryMemoryFD == -1)
@@ -47,7 +57,8 @@ Error SubprocessMemory::addMemoryDefinition(
     pid_t ProcessPID) {
   SharedMemoryNames.reserve(MemoryDefinitions.size());
   for (auto &[Name, MemVal] : MemoryDefinitions) {
-    std::string SharedMemoryName = "/" + std::to_string(ProcessPID) + "memdef" +
+    std::string SharedMemoryName = "/" + std::to_string(ProcessPID) + "t" +
+                                   std::to_string(getCurrentTID()) + "memdef" +
                                    std::to_string(MemVal.Index);
     SharedMemoryNames.push_back(SharedMemoryName);
     int SharedMemoryFD =
diff --git a/llvm/unittests/tools/llvm-exegesis/X86/SubprocessMemoryTest.cpp b/llvm/unittests/tools/llvm-exegesis/X86/SubprocessMemoryTest.cpp
index c07ec188a602c4..7c23e7b7e9c5a5 100644
--- a/llvm/unittests/tools/llvm-exegesis/X86/SubprocessMemoryTest.cpp
+++ b/llvm/unittests/tools/llvm-exegesis/X86/SubprocessMemoryTest.cpp
@@ -17,6 +17,7 @@
 #include <endian.h>
 #include <fcntl.h>
 #include <sys/mman.h>
+#include <sys/syscall.h>
 #include <unistd.h>
 #endif // __linux__
 
@@ -49,7 +50,9 @@ class SubprocessMemoryTest : public X86TestBase {
 
   std::string getSharedMemoryName(const unsigned TestNumber,
                                   const unsigned DefinitionNumber) {
-    return "/" + std::to_string(getSharedMemoryNumber(TestNumber)) + "memdef" +
+    long CurrentTID = syscall(SYS_gettid);
+    return "/" + std::to_string(getSharedMemoryNumber(TestNumber)) + "t" +
+           std::to_string(CurrentTID) + "memdef" +
            std::to_string(DefinitionNumber);
   }