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On Windows, retry process creation if we fail to reserve shared memory.

We've heard occasional reports of backend launch failing becausepgwin32_ReserveSharedMemoryRegion() fails, indicating that somethinghas already used that address space in the child process. It's notvery clear what, given that we disable ASLR in Windows builds, butsuspicion falls on antivirus products. It'd be better if we didn'thave to disable ASLR, anyway. So let's try to ameliorate the problemby retrying the process launch after such a failure, up to 100 times.Patch by me, based on previous work by Amit Kapila and others.This is a longstanding issue, so back-patch to all supported branches.Discussion:https://postgr.es/m/CAA4eK1+R6hSx6t_yvwtx+NRzneVp+MRqXAdGJZChcau8Uij-8g@mail.gmail.com

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src/backend/postmaster
- postmaster.c

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`‎src/backend/postmaster/postmaster.c`

Lines changed: 15 additions & 7 deletions

Original file line number	Diff line number	Diff line change
`@@ -4447,6 +4447,7 @@ internal_forkexec(int argc, char argv[], Port port)`
`4447`	`4447`	`staticpid_t`
`4448`	`4448`	`internal_forkexec(intargc,charargv[],Portport)`
`4449`	`4449`	`{`
	`4450`	`+intretry_count=0;`
`4450`	`4451`	`STARTUPINFOsi;`
`4451`	`4452`	`PROCESS_INFORMATIONpi;`
`4452`	`4453`	`inti;`
`@@ -4464,6 +4465,9 @@ internal_forkexec(int argc, char argv[], Port port)`
`4464`	`4465`	`Assert(strncmp(argv[1],"--fork",6)==0);`
`4465`	`4466`	`Assert(argv[2]==NULL);`
`4466`	`4467`
	`4468`	`+/* Resume here if we need to retry */`
	`4469`	`+retry:`
	`4470`	`+`
`4467`	`4471`	`/* Set up shared memory for parameter passing */`
`4468`	`4472`	`ZeroMemory(&sa,sizeof(sa));`
`4469`	`4473`	`sa.nLength=sizeof(sa);`
`@@ -4555,22 +4559,26 @@ internal_forkexec(int argc, char argv[], Port port)`
`4555`	`4559`
`4556`	`4560`	`/*`
`4557`	`4561`	`* Reserve the memory region used by our main shared memory segment before`
`4558`		`- * we resume the child process.`
	`4562`	`+ * we resume the child process. Normally this should succeed, but if ASLR`
	`4563`	`+ * is active then it might sometimes fail due to the stack or heap having`
	`4564`	`+ * gotten mapped into that range. In that case, just terminate the`
	`4565`	`+ * process and retry.`
`4559`	`4566`	`*/`
`4560`	`4567`	`if (!pgwin32_ReserveSharedMemoryRegion(pi.hProcess))`
`4561`	`4568`	`{`
`4562`		`-/*`
`4563`		`- * Failed to reserve the memory, so terminate the newly created`
`4564`		`- * process and give up.`
`4565`		`- */`
	`4569`	`+/* pgwin32_ReserveSharedMemoryRegion already made a log entry */`
`4566`	`4570`	`if (!TerminateProcess(pi.hProcess,255))`
`4567`	`4571`	`ereport(LOG,`
`4568`	`4572`	`(errmsg_internal("could not terminate process that failed to reserve memory: error code %lu",`
`4569`	`4573`	`GetLastError())));`
`4570`	`4574`	`CloseHandle(pi.hProcess);`
`4571`	`4575`	`CloseHandle(pi.hThread);`
`4572`		`-return-1;/* logging done made by`
`4573`		`- * pgwin32_ReserveSharedMemoryRegion() */`
	`4576`	`+if (++retry_count<100)`
	`4577`	`+gotoretry;`
	`4578`	`+ereport(LOG,`
	`4579`	`+(errmsg("giving up after too many tries to reserve shared memory"),`
	`4580`	`+errhint("This might be caused by ASLR or antivirus software.")));`
	`4581`	`+return-1;`
`4574`	`4582`	`}`
`4575`	`4583`
`4576`	`4584`	`/*`

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`‎src/backend/postmaster/postmaster.c`

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